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• Martian colonization using onsite construction requires a structural load combination. • Probable Martian structural loads are calculated and studied. • The valid data from landers, rovers, and orbiters are used for the study. • Martian structural loads are calculated based on the worst-case scenario. • A combination of loads is proposed for the design of Martian buildings. Multiplanetary life has been studied by scientists as a way to supply energy or sustain human life in the future. Mars is likely to be man's first destination, colonization using onsite structural construction would be one of the main options. The first step to designing a reliable building is to know the applied structural loads and to have an accurate design load combination. Due to lack of complete knowledge, short span of recorded data, Martian environment, and hazardous environment that Martian structures face, constructed Martian structures should behave appropriately under the highest likely live, dead and environmental loads either simultaneously or as a worst-case scenario. The present study evaluated and calculated probable Martian structural loads, including live, internal pressure, snow, gravity (dead), dust accumulation, thermal stress, wind, marsquake, asteroid, and meteoroid impact loads and their effects. Information was gathered from previous studies and valid data from Martian landers, rovers and orbiters. Wind loads were calculated based on the over 6.5 years of data recorded by Vikings 1 and 2, temperature and winds for InSight (TWINS) sensor. A wind shear exponent and wind profile have been proposed for a Martian flat terrain construction site. Marsquake lateral loads, frequency content and seismicity were assessed using data from the seismic experiment for interior structure (SEIS) and the Viking 2 seismometer. Considering the high influx of micrometeoroids, their penetration distance, impact loads and their effects on structures were calculated. The annual probability of an asteroid impact on a settlement was assessed for a 30-year mission. A load map for Martian residential buildings that considers the worst-case scenario in which a Martian structure should be designed based on them has been proposed. [ABSTRACT FROM AUTHOR]

On November 26th, 2018, the InSight spacecraft successfully landed on Mars after a 6-month journey. After a long deployment and commissioning phase, the SEIS (Seismic Experiment for Interior Structure) instrument was ready to monitor seismic events on the Elysium Planitia plain on the surface of Mars, coupled with the APSS (Auxiliary Payload Sensor Suite) weather station equipped with a magnetometer, wind sensors, and a pressure sensor. The InSight mission goal is to characterize the deep interior structure of Mars, including the thickness and structure of the crust, the composition and structure of the mantle, and the size of the core. Its nominal duration of two years (2019–2020) has yielded unprecedented results with the detection of the first Martian seismic events ever recorded, and the in-depth characterization of its atmosphere with the best weather station ever deployed on Mars. InSight has collected an outstanding amount of high-quality measurements that the scientific community will spend many years analyzing. The extended mission has started and covers the years 2021 and 2022. This paper will describe the operations of the SEIS experiment on Mars since landing, as well as the challenges of operating this instrument. Energy becomes increasingly limited for payloads on Mars due to a significant amount of dust accumulated on the solar panels and the many dust storms in the Martian atmosphere. A new activity was decided for the extended mission in 2021 which consisted in burying the seismometer cable (or tether) with Martian regolith collected locally using the robotic arm, in order to reduce the seismic noise from that subsystem. Preparation activities, testing, results, associated challenges and lessons learned will be presented. Moreover, the paper will address the challenges faced in carrying out operations with COVID-related constraints, as finding oneself operating a seismometer on Mars from home can be challenging. Finally, management of periods of solar conjunctions, during which communication between Earth and Mars is unavailable, will be addressed. • Deployment operations of a seismometer on Mars. • Detection of the first Mars seismic events. • Mars surface operations when energy is restricted. • Space operations in the context of COVID-19. • Unexpected tether burial and solar array cleaning operations on Mars. [ABSTRACT FROM AUTHOR]

We shed light on the nature and structure of the crust surrounding the Comoros Archipelago, western Indian Ocean, offering insights into the region's geological history and volcanic island formation. Our comprehensive study encompasses the acquisition of new, deeply penetrating seismic data from the SISMAORE cruise (refraction and reflection seismic), and the subsequent analysis of the characteristics and structure of the crust surrounding the Comoros Archipelago. Both the reflection seismic imaging and the velocity structure using ocean bottom seismometers indicate that the crust of the Comoros Basin exhibits oceanic characteristics, thus resolving previous controversies about its nature. The thickness of the oceanic crust ranges from 5.8 to 6.6 km in the north of the archipelago to 6–7.2 km within the Comoros Basin. The estimated roughness of the top basement in the Comoros Basin ranges from 110 to 200 m values typical of intermediate to slow spreading ridges, such as the extinct spreading centre in the West Somali Basin. The unloaded basement depth of the Comoros Basin closely matches the expected water-loaded subsidence for a Cretaceous or Jurassic oceanic lithosphere. In contrast, the West Somali Basin to the north of the Comoros Archipelago has shallower basement depths, potentially linked to recent volcanic activity along the archipelago. We propose that the pre-existing oceanic fracture zones in the West Somali Basin underwent reactivation, first during the Turonian period and later during the Late Eocene. These reactivated fracture zones may have acted as preferred pathways for the emplacement of the volcanic islands of the Comoros Archipelago. The EW trend of the archipelago appears to follow a marked change in the direction of these reactivated fracture zones, suggesting that the associated lithospheric weakening likely played a critical role in facilitating the formation of the Comoros Archipelago. • The crust of the Comoros Basin is oceanic, resolving past controversies. • Basement roughness is typical of intermediate-spreading ridges. • Unloaded basement depth matches Cretaceous or Jurassic oceanic lithosphere. • Comoros volcanic islands emplaced through re-activated fracture zones. • The Comoros Archipelago aligns with a change in the direction of the fracture zones. [ABSTRACT FROM AUTHOR]

We present C o n v E Q as a tool for discriminating seismic phases, leveraging artificial intelligence technique (Convolutional Neural Network) for short-time Frequency Transform of the seismic signal. Timely detection of the vertical (P) wave from an earthquake can generate a warning several tens of precious seconds before the more destructive waves strike. We propose a train-for-each-station approach for an Internet-of-Things-based Smart Earthquake Early Warning System, where lightweight neural networks trained for the seismic data belonging to each station are implemented on edge devices directly interfaced with seismometers. The approach has the potential to get the most from the sparse seismic network for Pakistan and other third-world countries. We train networks for multi-station and single-station data and achieve 96% and 99% accuracy, respectively, proving that train-for-each-station maximizes accuracy. The total processing time (including preprocessing and inference) is about 30 ms for each event, thus suitable for real-time deployment. We further compare the performance of C o n v E Q on simulated real-time data with several state-of-the-art contemporary algorithms. Our proposed approach demonstrates a robust response on diverse metrics. The C o n v E Q Z classifies the vertical seismic signal component with high accuracy and the C o n v E Q X can classify any seismic data component, inculcating robustness against connectivity issues. [Display omitted] • Earthquake phase classification, employing Neural Networks and frequency transform. • Train-for-each-station aimed at low-cost implementation for small seismic networks. • Superior performance on diverse metrics for a simulated real-time stream. • Train-on-any-channel strategy for robustness against data connectivity issues. [ABSTRACT FROM AUTHOR]

• Low-freq compensation algo improves the geophone's response, extending its natural freq from 4.5 Hz to < 0.2 Hz. • The improved short-period seismometer boast a compact design, affordability, and robust construction. • The bandwidth extension circuit has extremely low power consumption. • The improved short-period seismometer is well-suited for use in dense array observations. Short-period geophones are widely used instruments in dense seismic array investigations. However, inherent limitations in capturing low-frequency signals restrict their versatility. This study implements a low-frequency compensation algorithm via a state-variable filtering circuit to enhance the frequency response of a traditional short-period geophone. Through simulation experiments and vibration testing, we validated the performance of the proposed bandwidth-extension (BE) system. Additionally, time–frequency earthquake signal analysis compared outcomes between our BE seismometers, benchmark short-period seismometers, and high-fidelity broadband seismometers across three seismic events with epicentral distances up to 5,186 km. Results demonstrate the BE system successfully extends the natural frequency cutoff from 4.5 Hz to below 0.2 Hz while maintaining strong consistency with broadband counterparts. Moreover, negligible power demands (10 mW) facilitate embedding the BE circuit directly within acquisition hardware. Given these advantages, the BE method shows promise for upgrading future sensors of seismic networks to record low-frequency content with minimal costs. [ABSTRACT FROM AUTHOR]

The Southern Patagonian Icefield (SPI) lies above an area of slow convergence between Antarctic and South-America plates, where limited seismicity is recorded by global and regional seismic networks. To understand the seismic behavior of this zone, we analyze two years of continuous broad-band data recorded by 27 seismometers, deployed around the SPI. Substantial ice loss coupled with the unusually low viscosity of the underlying mantle is causing a rapid uplift. Our findings indicate that most of the seismicity occurs in the upper crust , likely associated with the (re)activation of regional compressive structures. However, earthquakes immediately beneath the SPI generally are shallower and show normal or strike-slip faulting. We suggest that this activity is promoted as a response to the crustal relaxation after rapid ice removal of SPI. The almost complete absence of interplate and intraslab events is consistent with a locked megathrust fault interface, highlighting the similarity of this region with the Cascadia subduction zone. • Shallow seismicity is observed in the majority in the area of southern Patagonia Icefield. • The inferred stress suggests the solid earth response to mass loss from the icefield as the major cause. • The almost complete absence of interplate earthquakes suggests that the megathrust may be locked. [ABSTRACT FROM AUTHOR]

South Korea has implemented borehole-type seismometers for reliable earthquake observations and earthquake early-warning systems, with approximately 85% of seismometers being replaced by borehole-type seismometers after the Gyeongju earthquake. Although these seismometers are more effective at detecting earthquakes owing to the reduced artificial ambient noise, they do not record surface-level shaking. Therefore, it is necessary to estimate ground surface shaking directly associated with potential damage when using borehole-type seismometers without surface sensors. This study investigated and compared various methods, including the stochastic point-source ground-motion model, transfer function based on ambient noise, and one-dimensional site response, to estimate horizontal seismograms of the ground surface. We assessed the accuracy of these methods by comparing the waveforms generated in event cases (magnitude from 2.5 to 5.8, with epicentral distances spanning 22 km–209 km) in terms of Fourier spectra, intensity, and spectral acceleration. Among the methods assessed, the transfer function approach, which does not account for the geophysical characteristics such as V S 30 , proved to be the most appropriate for correcting ground-surface effects. • Estimating seismic intensity measurements (IMs) at ground surface from borehole seismometers. • Approach for estimating IMs without ground surface seismometers. • Comparing methods: ambient noise transfer, point-source models, and 1D site response. [ABSTRACT FROM AUTHOR]

Seismometer component orientation is one of the most critical parameters for seismology, especially for methods that take wave field polarization effects into account, such as receiver functions, seismic anisotropy, surface wave dispersion and seismic tomography. Using P-wave particle motion combined with directional statistics, we estimated the orientation for 90 stations of the Brazilian Seismographic Network (RSBR), corresponding to 105 seismometers. The difference between the number of stations (90) and seismometers (105) is due to instrument replacement during station operation. We observed that 81 seismometers have an orientation of ±5° and 19 seismometers greater than ±5°. Only one seismometer has an orientation greater than 90° (BOAV station). ON and BR are the subnetworks of RSBR with the largest number of seismometers with orientation errors bigger than ±10° (6 for each one) and NB is the only subnetwork with no misoriented station. All the estimated orientations were close to the measured in the field, which is evidence that our approach is more accurate to detect misoriented stations than previous studies that analyzed the orientation of RSBR stations. The Watson's U2 statistical test indicated that the back azimuth deviations for Precambrian Basement and Phanerozoic Cover were significantly different, suggesting that the regional geology could affect back azimuth estimates. • P-wave particle motion was effective in detecting seismometer misorientation. • Directional statistics proved to be a suitable approach in back azimuth estimation. • Brazilian Seismographic Network has 14 stations with misoriented seismometers. • Stations deployed on Precambrian terrains tend to produce more accurate back azimuth estimates. [ABSTRACT FROM AUTHOR]

The Song Ma fault zone, located in northern Vietnam, plays a crucial role in understanding the mechanism and evolution of the collision zone between the Indian Plate and the Eurasian Plate. To investigate these mechanism and their evolution, we deployed a temporary broadband seismograph network surrounding the Song Ma fault to examine the body wave tomography and ultimately obtained the velocity structure. The results suggest that the variation in the velocity structure beneath the fault zone is due to the local geological structures and that earthquake clusters are situated between the Song Ma fault and the Son La fault in northern Vietnam. Our research findings demonstrate the transformation of the region from a collision zone to a strike-slip fault zone in terms of the velocity structure. This reflects the geological and geophysical evolution of the Song Ma area. This study is crucial for comprehending the active mechanism of the main shear zone in northern Vietnam and the crustal structure in the surrounding area. • Improved accuracy in event locations with closer clustering of relocated hypocenters. • Effective reduction of misfit in travel times, averaging 0.234 s. • Significance of understanding geological structures for precise seismic analysis. [ABSTRACT FROM AUTHOR]

The InSight mission's high-quality seismic data and cosmochemical models have demonstrated that Mars has a volatile-rich core. It is proposed that Mars formed early, before the solar nebular gas dispersed, and/or it accreted volatile-rich material to account for its volatile-rich interior. The early accreted Mars must have gravitationally attracted proto-atmosphere from the surrounding solar nebula. If its building blocks were rich in volatiles, it might have acquired impact-generated atmosphere during accretion. By considering the decay energy of the short-lived radionuclide (SLR) 26Al and the blanketing effect of the primordial and impact-generated atmosphere during the initial 10 Ma of the formation of the solar system, we present the results of numerical simulations carried out for the early thermal evolution and core formation of Mars. To explain the formation of a large iron core of Mars as suggested by the seismometer of InSight mission, we considered the 60% EH- and 40% CI-chondrite composition for the building blocks of Mars. The blanketing effect of impact generated H 2 O + CO 2 +CO + H 2 atmosphere caused the melting of surface silicates to form magma ocean at surface. We thoroughly examined the effects of several variables on the timing of complete core formation, including the initial water content in the accreted material, timescale of onset of accretion after the formation of CAIs, duration of accretion, absorption coefficient of CO 2 , efficiency of degassing of volatiles, and melting temperature. The results of present study show that the decay energy of SLR 26Al caused the widespread heating and melting of interior of Mars. For complete core formation, Mars must accrete within the first ∼2 Ma in order to explain the volatile-rich core. Further, the timescales of core formation were found to be strongly dependent on the assumed melting curve. For longer timescales of accretion, the interior of Mars experienced incomplete differentiation even by assuming high water content in the accreted material and larger absorption coefficient for CO 2. However, Mars does not have to accrete within 2 Ma for the core to fully develop if the Rayleigh- Taylor (RT) instability is present in the dense metallic layer on top of the undifferentiated interior. A short accretion time is only valid if RT-instability is neglected. Hence, we expect that the volatiles in the magma ocean could also be transferred to core by Rayleigh-Taylor instability. We also parameterized the thermal influence of gravitational heat produced during the differentiation of Mars to study its influence on the thermal evolution of the planet. The outcomes of the present work have implications to explain the timing of partition of volatiles in the Martian interior and formation of an early atmosphere on Mars. • Early thermal evolution of Mars with 60% EH- + 40% CI- chondrite composition has been studied. • Large iron core is formed at center as suggested by seismometer of InSight mission. • The impact generated H 2 O + CO 2 +CO + H 2 atmosphere formed magma ocean at surface during accretion. • Results of this study can explain the volatile-rich interior of Mars as suggested by InSight mission. [ABSTRACT FROM AUTHOR]

Very long oceanic transform faults do not just offset mid-oceanic ridges by hundreds of kilometers, but they also induce variations in the lithospheric structure and affect mantle melting, and hence the crustal accretion at the ridge-transform intersection (RTI). However, the deep structure of large offset RTIs remains unknown. Here, we present three-dimensional seismic tomography results (P- and S-wave velocities, Vp, Vs) in the vicinity of the eastern Romanche transform and the Mid-Atlantic Ridge in the equatorial Atlantic Ocean, using arrival times from microearthquakes recorded by a recent temporary array of seafloor seismometers. We find that normal to low Vp/Vs ratios (∼1.7) are observed at the Mid-Atlantic Ridge, representing weak serpentinization and the dominant magmatic processes, whereas high Vp/Vs ratios (∼1.8-1.95) are observed west of the RTI, at the eastern termination of the 2016 M w 7.1 earthquake. However, unusually low Vp/Vs ratios (∼1.6-1.7) are observed at 0-15 km depth and in the region of the 2016 M w 7.1 earthquake rupture zone. We suggest that the unusually low Vp/Vs ratios result from the presence of thick cracks at shallow depths (0-8 km) and/or the enrichment of orthopyroxene in the deep mantle (8-15 km). • 3-D Vp and Vs models for the Romanche eastern ridge-transform intersection. • Low Vp/Vs ratios (∼1.6-1.7) at depths of <15 km along the transform are observed. • The low ratios may be due to thick cracks and/or orthopyroxene enrichment. [ABSTRACT FROM AUTHOR]

The Xiaojiang Fault Zone (XJF) is an important boundary fault on the southeast border of the Tibetan Plateau, with a complex subterranean structure and strong tectonic activity. In the present study, 252 seismograph stations were deployed in the northern section of the XJF to collect ambient noise data in a span of 35 days. The minimum resolution attained was 2 km × 2 km to develop a high-precision underground velocity structure model. The velocity model helped in revealing that the low-velocity distribution originated below the XJF. It was also found that the fault, which is the primary channel for magma to rise, might be the cause of the upper crustal deformation of the XJF. The Dongchuan mining area is located to the west of the XJF, which has a low-velocity structure. However, the high-velocity structure appeared on both sides of the ore body. It is speculated that the ore was formed by magma intrusion. The intrusion serves as a heat source for the mining area and promotes deposit formation. [Display omitted] • A short-period dense array based ambient noise tomography for Xiaojiang fault. • High and low velocity 3D structure under Xiaojiang fault. • Deep ore metallogenesis constraints beneath the Dongchuan ore field. [ABSTRACT FROM AUTHOR]

Distributed acoustic sensing (DAS) using fiber-optic cables shows promise for rockfall monitoring by potentially offering high spatial resolution and wide coverage at lower costs. However, further research is needed to fully evaluate DAS performance for rockfall applications. This study assesses DAS capabilities for rockfall monitoring by analyzing DAS and seismometer recordings of 38 artificially triggered rockfalls with block masses ranging from 139.6 to 638 kg. Results demonstrate strong correlations between DAS waveforms and spectra with colocated seismometers, validating DAS data for detecting rockfall impacts. Fiber configuration impacted DAS sensitivity: fully in-contact cables improved signal-to-noise ratios and detection of high frequencies from 55 to 86 Hz. Analyses of seismic waves identified three distinct rock block propagation modes associated with intact, fragmenting, and collapse-triggering movements. While DAS signal feature values agreed with seismometers, no clear mass correlation emerged within the examined range. However, spectral features like frequency centroid (48.8 ± 6.5 Hz) and predominant frequency (41.0 ± 12.1 Hz) exhibited spatial stability across channels, indicating potential for event identification. Preliminary attempts to locate rockfall sources from DAS arrays proved feasible but require optimization. Overall, enhanced fiber coupling, identification of propagation modes, spatially-dependent analyses, and dense-array source location may enable DAS to complement sparse seismic networks for higher resolution, cost-effective rockfall monitoring. These insights could inform the development of improved rockfall monitoring strategies leveraging distributed fiber-optic sensing. • DAS signals match colocated seismometers, validating impact detection. • Fully coupled fiber improves DAS sensitivity/high-frequency detection up to 86 Hz. • Three distinct rock block propagation modes identified, linked to movements. • DAS spectral features spatially stable, indicating event identification potential. • Preliminary dense-array source location using DAS demonstrates feasibility. [ABSTRACT FROM AUTHOR]

This paper proposes a distributed principal component analysis seismic data compression algorithm based on fidelity restriction for non-cable seismic exploration systems. The proposed method compresses data effectively according to a customized fidelity. It first determines the cumulative contribution rate, then calculates the global eigenvector matrix, generates a projection in the seismographs and finally transmits the projected data. The numerical simulation results show that when the total waveform fidelity reaches 92%, the compression ratio still stands at 77 times or more. Furthermore, the field experiment also verifies the performance of the algorithm. • Avoiding large amount of seismic data transmission and storage by compression method. • Data compression and decompression are conducted by fidelity-restricted distributed principal component analysis. • It compresses data effectively according to customized fidelity. • It is applied in the non-cable self-positioning seismic exploration system. [ABSTRACT FROM AUTHOR]

The South China Sea (SCS) is a typical marginal sea basin formed by the seafloor spreading under the tectonic background of plate convergence. Many crustal-scale studies indicate that the SCS basin has undergone asymmetric spreading, multi-phase ridge jumps, and intense post-spreading volcanic activity. Due to the lack of seismic data in the oceanic basin of the SCS, it remains unclear about the scale and basin control of the Zhongnan fault, the magma source depth of the SCS basin, and the transport channel after the cessation of seafloor spreading. Phase velocity derived from ambient noise surface wave tomography may provide useful information to shed light on the mechanisms of the aforementioned problems. From October 2019 to July 2020, a passive source seismic experiment was carried out with many Ocean Bottom Seismometers (OBS) deployed in a broad area of the SCS. Based on the seismic ambient noise data recorded by 16 OBSs in the SCS basin, we inverted the phase velocity images over a period range of 10–20 s using ambient noise surface wave tomography. Our results indicate that the Zhongnan fault zone is a lithospheric-scale fault, which played a regulating role in the expansion of the SCS basin from the East Subbasin to the Southwest Subbasin. In addition, the low-velocity body in the north flank of the Southwest Subbasin extends from the post-spreading seamounts on the ocean crust to the uppermost mantle (i.e., about 10–30 km), which indicates an oblique magma migration during the post-spreading volcanism. • OBS ambient noise data reveal phase velocity images of the South China Sea basin. • The Zhongnan fault zone is a lithospheric-scale fault. • There is an oblique magma migration in the Southwest Subbasin on the post-spreading. [ABSTRACT FROM AUTHOR]

In this study, a semi-automated unsupervised clustering workflow is developed to classify ambient seismic noise from datasets acquired in an urban region, specifically using a pair of Tromino3G+ seismographs simultaneously recording high-gain velocity along two axes (north-south and east-west). A multi-day acquisition is used as a reference ambient seismic noise characterization of the area and to assess clusterability of the dataset. Additional 20-min datasets, acquired during and after anomalous urban activities are analyzed for a case study. The anomalous urban activity is due to street parties (large gatherings of people) during the Queen's University Homecoming celebrations in Kingston, Ontario. Unsupervised clustering methods are applied to classify ambient seismic events (coherent amplitude peaks in time-frequency space caused by uncontrolled natural and anthropogenic sources) directly from statistical properties of the event features (amplitude, frequency, bandwidth, duration, and azimuth relative to source). For urban ambient seismic noise, the signal sources may be numerous and unspecified a-priori and therefore unsupervised clustering methods are sought. Three clustering algorithms (k-Means, spectral, and agglomerative) are applied to characterize the urban region during the data collection campaigns. A probability density-based threshold modeled from the baseline dataset leads to the identification of event anomalies resulting from street party activity. The results provide insight into the utility of unsupervised clustering of ambient seismic noise for urban activity monitoring and indicate future work should include assessing the dependency of the workflow on the number of clusters and the selection of clustering methods. • Ambient seismic noise can be characterized in an urban environment. • Unsupervised clustering can aid in the characterization of an urban seismic baseline. • Anomalous events can be identified by comparing clusters. • Long- and short-term seismic datasets show similar event clusters. [ABSTRACT FROM AUTHOR]

Suruga Bay lies along the Tokai segment of the Nankai-trough, which last ruptured in the 1854 M8.4 Ansei-Tokai Earthquake, making it a potential locus for the next major earthquake on the Nankai-trough. Moderate size earthquakes have occurred in the Suruga Trough axial region (M6.5 in 2009 and M6.2 in 2011) that resulted in a prominent excitation of seismicity. Unfortunately, our ability to accurately locate these events is hampered by a sparse routine seismic observation network around the bay. In order to improve location accuracy, a total of 2 sets of 7 OBSs were deployed inside Suruga Bay, 6 from the spring of 2017, and an additional OBS from spring 2019. By combining the data from our OBS stations with that of existing land-based stations surrounding Suruga Bay, we were able to accurately relocate the observed seismic activity inside the Philippine Sea plate (PHS). Our combined processing revealed a 25° northwest-dipping 2–5 km wide zone on which the regional seismic activity occurs. Overall, seismic activity is observed to be 5–10 km shallower than previously determined from routine network data alone. A striking feature of the analyzed activity is the presence of a prominent strike-slip component in the focal mechanisms, which exhibit P-axes almost exclusively oriented towards the north. Furthermore, taking into consideration the apparent difference in the direction of the P-axis of the stress field to the calculated sense of movement of Izu peninsula by GNSS data, and the ongoing internal deformation observed by geodetic and geological data, we propose the existence of a shear zone inside the subducting PHS starting from the southern tip of Izu Peninsula and extending across the bay under Shizuoka city. This zone of strain partitioning acts as a buffer between the northward-colliding Izu Peninsula and the northwest-directed subduction of the PHS observed by GNSS. • First OBS deployment to monitor the Tokai Megathrust inside Suruga bay in 30 years, • Observed seismicity is 10 km shallower that reported in JMA catalogue, • Focal Mechanisms inside the PHS slab are mostly strike slip/oblique events, • Stress field on the megathrust boundary not favorably oriented for thrust faulting, • Slip partitioning sear zone inside the PHS slab impeding plate boundary rapture.. [ABSTRACT FROM AUTHOR]

Seismic reflections at the interface of heterogeneous porous media are significantly affected by the multi-scale fluid-flow losses. In this work, we study the seismic reflection dispersion from the ocean bottom separating seawater and heterogeneous porous seabed, described by the effective Biot theory where the mesoscopic loss is present. The analytical reflection coefficient is obtained based on the displacement potentials and suitable boundary conditions. Two reflection scenarios, including the water/water-bearing medium contact and water/gas-saturated medium interface, are considered. The shear-wave attenuation is also considered by using a Cole-Cole complex shear modulus. Numerical results showing the variation in reflection magnitude versus frequency and incidence angle are presented, revealing that the P-wave mesoscopic attenuation, complex shear modulus, boundary conditions and permeability can significantly affect the frequency and angle dependence of the reflection coefficients. Reflections at the water/gas-saturated medium interface exhibit quite different behaviors from those at the water/water-bearing medium contact. The open-pore interface gives frequency-dependent reflections, whereas in sealed-pore case, the reflection magnitudes remain unchanged for all frequencies, due to the fact that the interface degrades into a water/elastic solid one. The study can be relevant for reservoir prediction and fluid identification based on the reflected marine data. • Seismic reflection dispersion at the ocean bottom in the presence of mesoscopic loss is analyzed. • Impact of saturated fluid in porous seabed is investigated. • Effects of mesoscopic loss, complex shear modulus and interface conditions are discussed. [ABSTRACT FROM AUTHOR]

We image the Moho discontinuity and deep crustal layers by applying the Reverse Time Migration (RTM) method to wide-angle seismic (WAS) data that were acquired along two different profiles in NW and SE offshore Brazil, where the spacing between OBS is 12.5 km and 150 m between shots. The application of this method is quite uncommon to ocean bottom seismometers (OBS) data due to the OBS wide spacing deployment and low folds. We analyze the effectiveness of the RTM method when applied to the reflectivity of the WAS data. We imaged the structures by cross-correlating the forward and backward wavefields given by the acoustic seismic equation. This allowed us to use each interface crossed by a ray as both a source and a receiver. The velocity models used to perform RTM were previously obtained by applying a procedure of two-dimensional forward ray-tracing followed by a damped least-squares travel time inversion. The results obtained have an unexpected large contribution from the wavefield traveling as refractions within the Earth and, because of that, we can talk about recovering refractors from the RTM results. We obtained strong and continuous refractors for depths of 7–15 km that correspond to the basement and the Moho discontinuity. As we move landwards, the refractors that correspond to the Moho discontinuity disappear due to the deepening of the surface. Finally, we investigate how the slight change on the velocity model influences the result of the RTM method. The obtained results are promising for a wide range of applications at a crustal scale seismic exploration, with wide-angle seismic data. • Reverse time migration method with offshore Wide-Angle seismic. • Imaging of deep structures as Moho discontinuity and basement of the basin. with reverse time migration method. • Essential contribution of the refracted wave-field that allow to image the deep structures. • Effectiveness of the reverse time migration method for wide angle data. • Essential contribution in the absence of high resolution seismic data, since it is possible to image the deep structures without loosing the imaging of the shallow ones. [ABSTRACT FROM AUTHOR]

Abstract Erebus is an intraplate stratovolcano of phonolitic composition located at the southern end of Terror Rift within the West Antarctica Rift system. The volcanic edifice of Erebus exhibits a summit plateau that hosts the main crater and a smaller inner crater that contains a persistent lava lake. Volcano-seismic signals are recorded at Erebus by a permanent network of short-period and broadband seismometers installed around the volcano edifice. We investigate the duration-amplitude scaling of tremor recorded by the closest (~0.6–2 km) broadband stations to the inner crater during May 2002–April 2004 in order to elucidate the physical processes taking place at its source. After screening the data for signals related to non-volcanic sources such as iceberg calving, we obtained 72 tremor events. Spectral analysis reveals that these events were either harmonic exhibiting several overtones or broadband, but there were also mixed events that contained both of these two states. All tremor episodes considered in this study follow an exponential duration-amplitude distribution that implies a scale-bound source process. This precludes the possibility that any of these signals is related to iceberg calving near Ross island, or that rock fracturing processes play any role in tremor generation. The large viscosity of phonolitic magma (~105.3 Pa s) suggests that source mechanisms which require high flow speeds in order to excite tremor are unlikely to operate at Erebus. On the other hand, oscillations of CO 2 bubble clouds formed at localized asperities within the magma chamber represent a scale-bound source that is also consistent with the observed oxidation state of ascending gas and with the deep (~5–7 km) location of the tremor source. These results are important for understanding tremor processes at volcanoes which, similar to Erebus, exhibit vigorous convection in their shallow plumbing system. Highlights • Tremor events at Erebus exhibit an exponential scaling of duration-amplitude distribution. • The source of tremor at Erebus is scale-bound with characteristic scale length. • Resonance of bubble clouds within the plumbing system is a plausible tremor source. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Seismogenic characteristics near the NE rifted margin of the South China Sea are revealed. • NW-SE tensional stress controls the Taiwan collision-Manila subduction transition. • Intraslab pre-existing faults affect the seismogenic behavior of a convergent system. Abstract Based on the distribution of an earthquake swarm determined from an ocean bottom seismometer (OBS) network deployed from 20 August to 5 September 2015 in the northernmost part of the South China Sea (SCS) and data from inland seismic stations in Taiwan, we resolved a M L 4.1 earthquake occurring on 1 September 2015 as a NE-SW-trending left-lateral strike-slip event that ruptured along the pre-existing normal faults generated during the SCS opening phases. The direction of the T-axes derived from the M L 4.1 earthquake and the background seismicity off SW Taiwan present high consistency, indicating a stable dominant NW-SE tensional stress for the subducted Eurasian Plate (EUP). The distinct stress variations on the two sides of these reactivated NE-SW trending features suggest that the presence of pre-existing normal faults and other related processes may lessen the lateral resistance between the Taiwan collision and Manila subduction system, and facilitate the slab-pull process for the subducting portion, which may explain the NW-SE tensional stress environment near the transition boundary in the northernmost part of the SCS. [ABSTRACT FROM AUTHOR]

Abstract The northeastern margin of the South China Sea experienced continental rifting followed by magmatism in the Cenozoic. This evolution has strongly influenced the heterogeneity of its crustal structure. To gain insights into the spatial variation in crustal structure, data from 30 ocean bottom seismometers were used to forward model ten P -wave velocity models along both dip and strike directions. The Cenozoic strata (1.7–3.5 km/s), the Mesozoic strata (3.5–5.5 km/s), the crystalline crust (5.5–7.5 km/s) and high velocity lower crust (7.0–7.5 km/s) were identified based on P -wave velocities. Overall, the crust thins from ~25 km on the continental shelf to ~15 km on the slope, with thicker crust underneath the Dongsha Basin (a Mesozoic basin) but thinner crust underneath the pre-Cenozoic NW-trending fault zones. This difference in thickness is possibly controlled by different strength of inherited structures, i.e., the Dongsha Basin and the fault zones. Furthermore, a widespread high velocity lower crust layer, which resulted from the intrusion of a mafic sill complex, was observed over the shelf to slope. Mafic intrusions within the lower crust have uplifted the caprock on the shelf, and magma eruptions have formed many post-rift seamounts on the slope. The evidence suggests that post-rift magmatism overprinted the vertical crustal structure. We therefore propose that the heterogeneous crustal structures in this passive margin are an integrated result of segmental extension followed by magmatic overprinting. Highlights • Ten 2-D crustal models constrained by wide-angle seismic data are presented. • Pre-rift inherited structures controlled the lateral variation of crustal structure. • Post-rift magmatism overprinted the initial crustal structure and rifted features. [ABSTRACT FROM AUTHOR]

Abstract The experimental seismic behaviour of an isolation system, made of high damping rubber bearings, under low energy earthquakes is analysed. The seismically isolated building was instrumented by means of an accelerometer network. It was first characterized dynamically using also fifteen seismometers to record ambient vibrations. Then, all the events of the seismic sequence that struck Central Italy from August 2016 to January 2017 were recorded. These allowed evaluating the effects of earthquakes with different energy on the structure. Due to the long distances from the epicentres of these events, the analysis referred to the behaviour for very low shear strains in the rubber. The resonance frequencies of the base isolated building were much higher than those supposed in the design phase, but the filtering effect was still effective. One of the relative displacement history recorded during the strongest event was applied to the same devices used for the type tests at the construction time. The results obtained in terms of isolator stiffness were consistent with the experimental ones. Highlights • The good performance of the isolation system even under very low energy earthquakes. • The effective filtering due to the isolation, even though the resonance frequency was higher than the design one. • The variation of the isolator stiffness and damping for very low shear strains. [ABSTRACT FROM AUTHOR]

From the acoustic data acquired by the RHUM-RUM (Réunion Hotspot and Upper Mantle Réunions Unterer Mantel) Ocean Bottom Seismometer (OBS) network between October 2012 and November 2013, this study revealed baleen whale occurrence in the western Indian Ocean (IO). Low-frequency songs from three species (Antarctic Blue Whales, Pygmy Blue Whales and Fin Whales) as well as P-calls (or Spot-calls) from an unknown species were recorded on the dataset. The wide arrangement of the OBS network (2000 km × 2000 km) provided valuable information to draw seasonal patterns of occurrence and distribution all over the area. These species occurred sympatrically in the western IO, at least during austral autumn months emphasizing the importance of this region for these populations. This data set helped to refine the knowledge on their spatio-temporal distribution and complete the picture built by previous studies. A tighter sub-network of 8 OBSs deployed on the South West Indian Ridge provided ideal inter-sensor spacing for whale tracking. We demonstrated the capability of such array of detecting and tracking the three different whale species up to 50 km and for several hours. As a result and to understand the effect of acoustic wave propagation, songs from the tracking were described at a close and remote distance of the sensor. This work could also help to understand the local behavior of these species during austral autumn months in this area of the western Indian Ocean. [ABSTRACT FROM AUTHOR]

Abstract The 2013 Craig, Alaska M W 7.5 earthquake ruptured along ∼150 km of the Queen Charlotte Fault (QCF), a right-lateral strike-slip plate boundary fault separating the Pacific and North American plates. Regional shear wave analyses suggest that the Craig earthquake rupture propagated in the northward direction faster than the S-wave (supershear). Theoretical studies suggest that a bimaterial interface, such as that along the QCF, which separates oceanic and continental crust with differing elastic properties, can promote supershear rupture propagation. We deployed short-period ocean-bottom seismometers (OBS) as a part of a rapid-response effort less than four months after the Craig earthquake mainshock. During a 21-day period, 1,133 aftershocks were recorded by 8 OBS instruments. Aftershock spatial distribution indicates that the base of the seismogenic zone along the QCF approaches ∼25 km depth, consistent with a thermally-controlled fault rheology expected for igneous rocks at oceanic transform faults. The spatial distribution also provides supporting evidence for a previously hypothesized active strand of the QCF system within the Pacific Plate. Tomographic traveltime inversion for velocity structure indicates a low-velocity (V P and V S) zone on the Pacific side of the plate boundary at 5–20 km depths, where Neogene Pacific crust and upper mantle seismic velocities average ∼3–11% slower than the North American side, where the Paleozoic North American crust is seismically faster. Our results suggest that elastic properties along the studied portion of the QCF are different than those of a simple oceanic–continental plate boundary fault. In our study region, velocity structure across the QCF, while bimaterial, does not support faster material on the west side of the fault, which has been proposed as one possible explanation for northward supershear propagation during the Craig earthquake. Instead, we image low-velocity material on the west side of the fault. Explanations could include that part of the rupture was subshear, or that fault damage zone properties or fault smoothness are more important controls on supershear rupture than a bimaterial contrast. Highlights • Pacific velocities are slower than North American velocities at seismogenic depths. • Base of seismogenic zone approaches 25 km, consistent with oceanic deformation. • Pacific crust may be weaker than North American crust in the Craig earthquake area. • The bimaterial contrast was not likely a control on Craig supershear directionality. [ABSTRACT FROM AUTHOR]

Abstract The Kilauea volcano on the Hawaii island started erupting on 3rd May 2018 after an earthquake of magnitude 5.0. The initial volcano eruption and the subsequent earthquakes resulted in the opening of new volcanic fissures, continuous lava flow at the lower east rift zone and the collapse of the summit caldera floor. All these activities continued until the 1st week of August 2018. The Small Baseline Subset (SBAS) technique is an advanced form of Differential Interferometry (DInSAR) which is capable of monitoring surface deformations with millimetre level accuracy. SBAS technique was utilised here for estimating the surface deformation on Hawaii island due to the volcanic episode. InSAR coherence technique was also utilised in this study for localised analysis at the summit and at the lower east rift zone to detect the time series deformation information and lava flow patterns. 14 interferometric datasets acquired by the ESA's Sentinel-1 C-band satellite from April 2018 to September 2018 were used in this study. The data acquired by the seismometers installed at Kilauea by Hawaii Volcano Observatory, the SWIR band of Sentinel-2 and the thermal band of Landsat-8 were used to correlate and verify the results obtained through the SBAS and InSAR coherence analysis. The combined interpretation of results obtained from all the sources gave insights about the underground magma conduit system, surface deformations, lava flow channels and the correlation between the magmatic and seismic activity happened there which are discussed in detail in this paper. Highlights • Detected subsidence at the Kilauea summit and Puu Oo crater due to magma withdrawal • Increased seismic activity at summit due to Caldera floor collapse • Open channel lava flow from fissures at Leilani Estates • Lava delta formation due to ocean entry of lava flowing through open channel • Sub-terrain magma conduit from summit reservoir to Leilani Estates [ABSTRACT FROM AUTHOR]

Abstract The alongshore distribution of wave energy is believed to be an important control on the spatial variability of coastal erosion. There is, however, a lack of field data quantifying the alongshore variability in wave energy on rock coasts, whereby the relative control of coastline geometry versus foreshore characteristics on wave energy delivery remains unclear. A number of studies have identified high-frequency cliff-top ground shaking to be generated by wave impacts at the cliff toe during high tides (HT). To capture the variability of wave-cliff impact energy along-coast, we installed an array of cliff-top seismometers along a 1 km stretch of coastline in North Yorkshire, UK. Our aim is to constrain how wave energy transfer to the cliff toe varies, and to examine the relative energy transfer around typical coastline features, including a bay and headlands. Whilst the greatest HT ground motion energy is recorded at a headland and the lowest at the centre of the bay (5% of that observed at the headland), we identify no systematic alongshore variation in the HT ground motion energy that can be related to coastline morphology. We also note considerable variation between features of similar form: the total HT ground motion energy at one headland is only 49% of the next headland 1 km alongshore. Between neighbouring sites within the bay, separated by only 100 m, we observe up to an order of magnitude difference in ground motion energy transfer. Our results demonstrate the importance of the foreshore in driving the variations in energy delivery that we observe. Local alterations in water depth and foreshore topography control the alongshore distribution of wave energy available to generate cliff HT ground motions. Importantly, this apparently local effect overrides the influence of macroscale coastal planform morphology, which has previously been assumed to be the dominant control. The results show that foreshore characteristics that hold influence over wave energy transfer vary significantly over short (~100 m) distances, and so we expect erosion controlled by wave impacts to vary over similar scales. Highlights • Cliff-top ground motions vary significantly over short alongshore distances. • There is no systematic alongshore pattern in high-frequency ground motion energy. • Foreshore characteristics influence alongshore distribution of wave energy. • Foreshore characteristics override the influence of coastal planform morphology. • Foreshore characteristics that influence wave energy vary over short distances. [ABSTRACT FROM AUTHOR]

Highlights • FBG geophone with acceleration limit is designed for weak signal detection. • Environmental tests verify its reliability as oil & gas industry product. • FBG geophone shows higher SNR compared to conventional moving-coil geophone. • Seismic cross-section profiles were obtained by FBG geophone array in field tests. Abstract A fiber Bragg grating (FBG) based geophone is designed for low-frequency signal detection. It has high acceleration response of about 60 dB re pm/g in a low frequency range of 5–60 Hz. However, the basic sensing principle of stretching FBG requires much more delicate and reliable packaging design and technology. Especially the high sensitivity at low frequency challenges the reliability in packaging, transportation and installation of sensor. To guarantee normal operation in field test and practical application, an acceleration amplitude restriction is added in the mechanical design of the FBG geophone. Then a series of environmental and reliability tests have been proceeded with online or offline monitoring of its working performance, including high & low temperature test, vibration test, shock test and tensile test, strictly according to National standard and Oil & Gas Industry Standard. The experimental results indicate that our FBG geophone meet the criterion of oil and gas industry product and is capable of field application. Finally, in the filed blasting tests, the seismic cross-section profile was obtained by use of FBG geophone array which shows the advantage in low frequency signal acquisition compared to conventional move-coil geophone. [ABSTRACT FROM AUTHOR]

Abstract Anthropogenic activity related to the extraction of gas and oil, raw materials or water pumping leads to slow or rapid ground deformation. The ground motion rate is related to the type of the mined material, geological conditions, mining methods and other factors. Ground subsidence resulting from the collapse of underground post-mining voids occurs gradually. Mining-induced earthquakes and seismic earthquakes are largely unpredictable and have an adverse impact on the local inhabitants and buildings. For this reason, monitoring of this phenomenon is a challenge. The application of interferometric SAR for the evaluation of ground movement has brought satisfactory results over the past twenty years mainly in the regions where no other measurements were conducted during ground subsidence. In this paper we have examined a mining-induced earthquake with a magnitude 4.5 which occurred in an underground copper ore mine in Poland on 29th November 2016 and caused eight fatalities. It also had an impact on ground surface deformation in the vicinity of the mine tailings. An assessment of the earthquake-related impact on surface movement was carried out by Sentinel-1 TOPS time series interferometry. The velocity of ground movement and the scale of the phenomenon were investigated. In addition, the impact of the mining-induced earthquake on Zelazny Most mine tailings site was analyzed. Moreover, the process of dynamic ground compaction was also investigated in detail. Ground movement following the mine earthquake was explored. Two time phases of the movements were determined. The first phase of dynamic ground displacement was rapid and 90% of total ground deformation appeared on the surface within 7 days. The second phase of displacement was a 'vanishing' one; it lasted for approx. 3 weeks and 10% of ground deformation appeared on the surface. The study revealed that the maximum observed ground subsidence did not exceed 9 cm. The presented results contribute to a better understanding of post-earthquake ground deformations in the light of their spatial distribution in time. Highlights • Sentinel-1 interferometry is used to assess subsidence caused by mining-induced earthquake (M W 4.5). • About 92% of total subsidence occurred within 48 h after mining-induced earthquake. • Substantial ground movement stopped 7 days after the earthquake (M W 4.5). • Contribution to studies on ground movements which result from mining-induced earthquake. [ABSTRACT FROM AUTHOR]

Highlights • First high-resolution data from a creepmeter array collocated with seismometers. • Monitored faults are highly susceptible to dynamically triggered shallow slip. • Far-field triggering relates to surface waves, near-field triggering to body waves. • Large earthquakes can trigger shallow slip events over distances of 103–105 km. • Triggered shallow slip scales with seismic energy density. Abstract The M w = 8.8 Maule Earthquake of February 27, 2010, remotely triggered minor surface displacement along the Atacama Fault System in Northern Chile located 1500–1800 km from the epicenter. Here we present evidence that surface displacement events recorded by the IPOC (Integrated Plate Boundary Observatory in N-Chile) Creepmeter Array are related to earthquakes on the underlying subduction zone interface or to large earthquakes around the world. Our observations document dynamic triggering of shallow slip on faults in a forearc setting. Continuous monitoring revealed that up to 30 displacement events per year occur on the monitored fault segments, >90% of them triggered by earthquakes in the near or far field synchronous to the passage of the seismic wave. We can clearly attribute far field triggering to the passage of the surface wave and near field triggering to the passage of the body wave. The most distant triggered displacement event monitored occurred after the 2011, M w = 9.0 Tohoku-Oki Earthquake located 16 468 km away following the passage of large amplitude SS waves. Comparing the triggered displacement events with other triggered phenomena like seismicity, volcanic eruptions, hydrological changes as well as with data from the California Creepmeter Array we find that the seismic energy density appropriately describes a magnitude–distance scaling relationship of slip triggering. Finally, the observed surface displacement is found to not occur by continuous creep, but rather through nearly exclusively discrete displacement events. [ABSTRACT FROM AUTHOR]

Abstract The origin and evolution of magmatism in rifting margins are a fundamental geological subject, and remain the focus of intense studies. Unlike the classical magma-poor and magma-rich rifting margins, the northern margin of the South China Sea (SCS) exhibits a strong post-rift magmatism, but the evolution and mechanism of this behavior are still poorly understood. In this work we investigate the detailed structural features of the post-rift magmatism in the crust of the SCS northern margin. Our analysis is based on wide-angle and multichannel reflection seismic data, combined with previous seismological results. Our results show a wide distribution of shallow igneous sills and intrusions. These features are spatially and tectonically linked to the lower crustal high-velocity bodies (HVBs) and submarine volcanism, indicating a causative connection between the three features. Considering the existence of an obvious low-velocity branch of the Hainan plume in the northern SCS and uplift of the lithosphere-asthenosphere boundary, we propose that the HVBs reflect consolidated mafic intrusions which formed the lower crustal reservoirs feeding the overlying igneous sills and intrusions. In the SCS northern margin where abundant extensional and detachment faults can act as magmatic channels, such a dynamic process might cause post-rift volcanism. Our results suggest that the crustal magmatic system of post-rift volcanism has a multilevel upward migration mode, and the HVBs in the lower crust could be the product of post-rift magmatism, further indicating that the SCS northern margin had a magma-poor property at the rifting phase but has undergone a strong magmatic rejuvenation by the subsequent mantle plume. Highlights • Revealing seismic features of post-rift magmatism in the SCS northern margin • Lower crustal HVBs link to shallow igneous sills/intrusions and submarine volcanism. • The crustal plumbing system has a multilevel magmatic-transport mode. • Magma-poor SCS northern margin was rejuvenated by the Hainan mantle plume. [ABSTRACT FROM AUTHOR]

We present SKS splitting measurements in the Western Indian Ocean, recorded on 20 land and 57 seafloor seismometers deployed by the RHUM-RUM experiment (Réunion Hotspot and Upper Mantle – Réunions Unterer Mantel). We discuss our splitting observations within their geodynamic settings and compare them to SKS splitting parameters predicted from an azimuthally anisotropic Rayleigh wave tomography model that includes the RHUM-RUM data. We find that anisotropic directions poorly correlate with the present-day motion of the Somali plate, which at <2.6 cm/yr may be too slow to cause strongly sheared fabric in the asthenosphere. Fast split directions ( Φ ) between La Réunion and the Central Indian Ridge (CIR) trend E–W and provide strong, first seismological evidence for near-horizontal flow in the asthenosphere that connects the Réunion mantle upwelling with the CIR, supporting a long-standing hypothesis on plume–ridge interaction. In the vicinity of the Réunion hotspot, we observe a seismic anisotropy pattern indicative of a parabolic asthenospheric flow controlled by the Réunion mantle upwelling and its consecutive asthenospheric spreading. We furthermore observe ridge-normal Φ along the CIR and ridge-parallel Φ along the Southwest Indian Ridge (SWIR), both mainly attributed to asthenospheric mantle flows. In the Mozambique Channel between East-Africa and Madagascar, we attribute E–W trending Φ to frozen lithospheric structures, recording the paleo-orientation of the spreading ridges that enabled Madagascar's separation away from Africa. Based on the synopsis of this and previous SKS splitting studies at mid-ocean ridges, we propose that ridge-normal Φ may develop at fast and intermediate spreading ridges (e.g., CIR and East Pacific Rise) and ridge-parallel Φ could be characteristic to slow spreading ridges (e.g., SWIR, Mid-Atlantic Ridge and the paleo-ridges in the Mozambique Channel). [ABSTRACT FROM AUTHOR]

A full-scale symmetric structure was constructed in the Euroseistest experimental facility in the North of Thessaloniki, Greece, to promote studies of wave propagation and soil-structure interaction in real field conditions. The 3-by-3-by-5 m model structure, called EuroProteas , comprises of a reinforced concrete slab resting on the soil surface, and four steel columns (with or without bracing) supporting one (or two) reinforced concrete slabs acting as the superstructure mass. The reconfigurable stiffness and mass of the structure, in conjunction with the well-known soil profile in Euroseistest, allow for the investigation of soil-structure interaction for different structure-to-soil stiffness ratios. More than 80 accelerometers and seismometers on the structure and on the soil surface, as well as down to a depth of 12 m, were used to record the response of the soil-structure system during a set of field tests under ambient noise, free- and forced-vibration loading. Following a detailed description of the EuroProteas testing facility and the experimental campaign, field evidence on critical SSI issues is reported based on recorded data. Particular emphasis is placed on the period elongation and damping of the SSI system due to the foundation soil compliance by employing well-known data interpretation methods. Softening of the soil-structure system, reflected in the elongation of the SSI period with respect to its fixed-base counterpart, and attenuation of soil response away from the oscillating structure with increasing amplitude of loading, are discussed. [ABSTRACT FROM AUTHOR]

At mid-ocean-ridge spreading centers, the separation of lithospheric plates induces upwelling and pressure-release melting in the upper mantle. Many questions remain about the associated flow pattern, melt distribution, and the interaction of spreading centers with hotspots. Based on the propagation of Rayleigh waves across arrays of ocean-bottom seismometers, we present shear wave attenuation and velocity models in the vicinity of the Juan de Fuca plate with the best resolution to date of any spreading center. There is strong attenuation centered at depths of 70–80 km, just below the expected dry solidus. The top of the attenuating region is somewhat deeper than predicted for the thermal effects of passive mantle upwelling beneath the spreading center. The shear velocity structure shows the lowest velocities west of the spreading center, particularly near Axial Seamount and high velocities east of the axis extending to a greater depth than predicted by the passive flow model. Together, these observations support a model in which buoyant upwelling and melt extraction west of the spreading center first depletes and dehydrates the mantle above the dry solidus and then the associated downwelling carries depleted, melt-free, residual mantle downward beneath the Juan de Fuca plate. The shear velocities and attenuation can be well matched with a model in which the dominant changes in the physical properties occur just before the onset of melting. [ABSTRACT FROM AUTHOR]

We present locations of almost 14,000 events from the first six months of the Petrinja (Croatia) earthquakes sequence (mainshock 29 December 2020, M w 6.4). The catalogue is estimated complete for M L ≥ 1.20. Initially sparse local seismograph network was densified a week after the mainshock, which reduced uncertainties of focal locations by about 75%. Source-specific station corrections were used in an iterative location scheme. The hypocentres were located with 30 different sets of velocity models and program control parameters in order to gain insight into the epistemic uncertainty of each earthquake location. The bulk of epicentres are located close to, and to the SE of the causative, dextral strike-slip Petrinja fault, but considerable activity has been triggered on smaller faults, up to 25 km away. About a half of the 78 first-motion polarity focal mechanism solutions (FMS) from the full first year of activity were found to have mechanisms similar to the foreshock, the mainshock and the largest of aftershocks, while the rest indicated almost pure reverse faulting. Strike-slip mechanisms occurred more often close to the main fault. The P-axes of FMS for aftershocks were found to be on the average rotated by 16° clockwise with respect to the P-axis of the mainshock, regardless of the style of faulting. The spatial distribution of aftershocks coincides very well with the areas of positive Coulomb stress change caused by the mainshock rupture. The inferred cut-off seismogenic depth in the area (7–10 km), estimated on the basis of published values of the geothermal gradient and the assumption of predominantly granitic upper crust, is considerably shallower than the depth of the deepest reliably located aftershocks (16–18 km). This fact may be explained by considering ophiolite-dominated crust, and by increased strain rate during the sequence, which raises the ability of crustal rocks for brittle failure. • Almost 14,000 aftershocks of the Petrinja earthquake sequence have been located. • The accuracy of locations markedly increased after installation of local networks. • Epistemic uncertainties of locations are estimated by velocity model variation. • Strike-slip and pure reverse focal mechanisms are observed for 78 events. • Coulomb stress change trigger zones correspond to aftershock locations. [ABSTRACT FROM AUTHOR]

Utilizing the surface-wave (Rayleigh-wave) dispersion properties to estimate subsurface S-wave velocity structure has become a popular method due to simple data collection and analysis procedure during the past decades. In particular, the promotion of distributed acoustic sensing (DAS) technique enhances its popularity due to the low-cost of ultra-dense observations. Moreover, under the same exploration requirement, the cost of the DAS data collection is much lower than that of the traditional acquisition implemented by the nodal seismographs. Therefore, it is necessary to expand the DAS application. Here, the multimodal surface-wave dispersion curves are successfully extracted from the phase-weighted stack of cross-correlation functions (CCFs) of the DAS data collected at Garner Valley Downhole Array field site, California by the proposed cylindrical-wave phase-shift. Then, the dispersion curves are inverted by the inversion workflow (expected to avoid the mode-misidentification) proposed by Yan et al. (2022a), consisting of staging strategy and pattern search with embedded Kuhn-Munkres (PSEKM) algorithm. Compared with other inversion schemes, the novel inversion method allows the presence of the observed values without prior mode-order definition in the inversion system, which omits the tedious and risky manual mode identification, and the mode-orders would be predicted dynamically during the inversion. The dispersion fittings for certain survey points indicate that the mode losses and aliasings appear to be widespread for the surface waves recorded on the free-surface. Finally, the S-wave velocity tomogram consistent with the geological materials of survey area is revealed. Our study demonstrates the feasibility of extracting the DAS-derived multimodal dispersion information and consequently obtaining a physical-reasonable subsurface S-wave velocity model. • Propose the cylindrical-wave phase-shift for dispersion spectrum calculation. • Construct a dedicated workflow for DAS data analysis. • The inversion method without high-mode order-label is adopted. • Mode-losses and aliasings of dispersion curves are revealed by our method. [ABSTRACT FROM AUTHOR]

Volcanic eruptions are sometimes preceded by tilt changes that are an indicator of immediate pre-eruptive processes. In this study, the tilt changes before all monitored eruptions in Japan were surveyed for the first time to address the generality and common features of these signals. An automated procedure was devised to identify tilt changes. The results showed that approximately half of the analyzed eruptions were preceded by tilt changes. Detection ratios depended on station locations, and approximately 10–20% of the total waveforms consisted of detectable tilt changes. Broadband seismic records, when integrated into displacements, showed detection ratios comparable to those of tiltmeter records. The lead times and durations of the tilt changes showed large variations. The durations correlated with amplitudes, although with considerable scatter. Both accelerating and decelerating types of tilt changes were common, and their ratios depended on the volcanoes. These are the first findings on the nature of pre-eruptive tilt changes from many volcanoes, and the waveform analysis procedure proposed in this paper is applicable to other regions. Future works involve extending this study to datasets from other regions, detecting tilt changes from continuous records, applying the proposed method to an early warning system, and detecting longer tilt changes, which require that the proposed approach be improved by subsequent studies. [Display omitted] • All pre-eruptive tilt changes in Japan were systematically surveyed. • Approximately half of the eruptions were preceded by tilt changes. • Broadband seismometers detected tilt changes at rates comparable to tiltmeters. • Durations of the tilt changes weakly correlated with amplitudes [ABSTRACT FROM AUTHOR]

Deep-sea sediments record the geological and climate history of the Earth. The seismic properties of these sediments, namely the P- and S-wave velocities, depend on their chemical compositions, grain size, age and depth of burial, which, in turn, influence the porosity. We use multichannel seismic reflection data to estimate the sediment thickness and P-wave velocity over 4-74 Ma old oceanic crust on the African Plate and 3-27 Ma old crust on the South American Plate in the equatorial Atlantic Region. We then use the P-to-S converted waves from the basement-sediment interface recorded by 69 multi-component ocean bottom seismometers to determine the P- and S-wave velocity ratios ( V P V S ) over 3 to 74 Ma. We find that the V P V S decreases from 8.9 ± 2.0 at 3 Ma to 5.0 ± 1.0 at 17 Ma but abruptly increases to 19.5 ± 2.8 at 37.5 Ma. Then, it gradually decreases for crustal ages >37 Ma, reaching 7.0 ± 0.3 at 74 Ma. These variations are almost symmetric across the Mid-Atlantic Ridge over 4-27 Ma, suggesting a relation to climate change rather than regional effects. We estimate the average sediment porosity using the V P V S and find that the average porosity decreases from 89.2 ± 1.5% at 37.5 Ma to 69.9 ± 1.2% at 74 Ma, possibly associated with accumulation of terrigenous input from Africa. Between 4 and 37 Ma, the porosity fluctuates between 70% and 85%. Such a fluctuation correlates well with the decrease in the global atmospheric CO 2 from 800 ppm to 400 ppm during the Oligocene and with carbonate compensation depth, which are possibly related to fauna/flora diversification and calcareous sediment accumulation. The variation in porosity at 23 and 17 Ma also appears to be linked with major climate shifts, suggesting that sediment porosity could be used to shed light on the past climate and fauna/flora characterization. • We use seismic data to characterize sediment porosity in the equatorial Atlantic. • Porosity has anomalous and symmetric trend across the MidAtlantic Ridge. • We show that in deep-sea environments, climate affects the sediment porosity. • Our porosity results correlate with the climate history of the Oligocene and Miocene. [ABSTRACT FROM AUTHOR]

The exploration of active faults provides a basis for earthquake disaster prevention and migration. Active seismic survey is generally considered to be one of the most effective active fault exploration techniques because of its high resolution and deep penetration. However, this technique always yields low-resolution seismic data of a near-surface active fault. This limitation can be improved with the increase of sensor density with conventional nodal seismometers, but this is an expensive approach for active fault exploration. Distributed Acoustic Sensing (DAS) seems to be an ideal technique to replace traditional nodal seismometer surveys because it has the advantages of high-density sensors, many channels, and low cost. However, the applicability of active seismic surveys via DAS in the exploration of active faults remains unknown. Here, we designed an active seismic survey test in the Datong Basin, North China, focusing on a graben marked by well-developed normal faults in and around the basin. We selected a buried active fault identified in our previous active seismic profile, and DAS and nodal seismometers were deployed over a possible site of the active fault to conduct a comparative active seismic survey using a tamping machine. The comparisons with data recorded by three-component nodal seismometers demonstrate that DAS can also provide effective near-surface active fault information, and the imaging results also showed that the combination of conventional telecommunication fibre-optic cable and active seismic data processing techniques can be effectively used for near-surface active fault exploration, which is helpful in determining the true location of an active fault. • DAS can be used in the exploration of near-surface active faults as a replacement of conventional nodal seismometers. • High-resolution near-surface active fault are derived from conventional reflection seismic surveys based on DAS. • The diffracted wave in DAS data with high spatial sampling rate can be used to locate the near-surface active fault. [ABSTRACT FROM AUTHOR]

During the SALSA experiment, in 2014, twelve combined wide-angle refraction and coincident multi-channel seismic profiles were acquired in the Jequitinhonha-Almada-Camamu, Jacuípe, and Sergipe-Alagoas basins, NE Brazil. Profile SL09 images the Almada-Camamu basin and the São Francisco craton, with 18 four-channel ocean-bottom seismometers and 22 land stations. The datasets were forward modelled and combined with pre-stack depth migration to increase the horizontal resolution of the velocity models. Our results show that sediment thickness varies between 3.8 km in the oceanward part of the profile, 4.3 km in the Almada basin and 6.5 km in the Camamu basin. Crustal thickness at the north-western edge of the profile is of around 40 km, with velocity gradients indicating a continental origin. The Camamu basin, which corresponds to the triple junction between the aborted N–S oriented Tucano rift, the SW-NE oriented Jacuipe-Sergipe-Alagoas branch, and the N–S Jequitinhonha-Almada branch, presents two crustal layers: a very thin upper layer, about 1.5 km thick, which increases seawards to 3 km in the Almada basin, and an higher velocity (HV) layer (6.8–7.2 km/s) about 4 km thick. This lower layer gradually disappears in the Almada basin. At the south-eastern edge of the profile, the resolution is lower but the thickness of the crust seems to increase up to 5 km. Deep wide-angle reflections indicate upper mantle stratification. Crustal organisation and P-wave propagation velocities in the Almada and Camamu basins indicate a transitional crust domain of exhumed continental crust affinity. In the Camamu triple junction and beneath this thin exhumed continental crust, the HV layer may probably reflect intruded materials. No exhumed upper mantle is observed along the entire profile. The easternmost part of the profile may correspond to a proto-oceanic crust. Typical oceanic crust is never imaged along the 260 km-long offshore profile. • The transitional domain in the Almada and Camamu basins has exhumed continental crust affinity. • The distal basin may correspond to a proto-oceanic domain. • Typical oceanic crust in not imaged on profile SL09. • Necking occurs within 60 km. [ABSTRACT FROM AUTHOR]

The North Natal valley (NNV), South Mozambique margin, is a key area for the understanding of the SW Indian Ocean history since the Gondwana break-up as its crustal nature and geometry strongly impacted the reconstruction of the paleogeography before the rifting. It is also of considerable importance for the understanding of the evolution of a margin system as the NNV is situated at the transition between divergent and strike-slip segments and at the conjunction of Oxfordian-Kimmeridgian Indian Ocean and the Valanginian-Aptian Atlantic one. As one part of the PAMELA project (PAssive Margins Exploration Laboratories), the NNV and the East Limpopo margin have been investigated during the MOZ3/5 cruise (2016), through the acquisition of 7 intersecting wide-angle profiles and coincident marine multichannel (720 traces) seismic as well as potential field data. Simultaneously, land seismometers were deployed in the Mozambique coastal plain (MCP), extending six of those profiles on land for about 100 km in order to provide information on the onshore-offshore transition. Wide-angle seismic data are of major importance as they can highlight constraints on the crustal structure of the margin and the position of the continent-ocean boundary in an area where the crustal nature is poorly known and largely controversial. The MOZ3/5 data set therefore reveals new essential constraints for kinematic reconstructions. This work presents results on the crustal structure from P-waves velocity modeling along two E -W wide-angle profiles (MZ1 and MZ2) through the NNV, from the Lebombo Monocline to the Mozambique Basin (MB), and crossing the Mozambique Fracture Zone (MFZ). The new geophysical data reveals an upper sedimentary sequence characterized by low velocities generally not exceeding 3 km/s, and up to 3 km thick where a major contouritic structure was observed. This feature formes together with several other contouritic structures, a N-S alignment just west of the MFZ, which produces high positive gravity anomalies, previously thought to be related to the magmatism that built the Galathea and Dana Plateaus. High velocity lenses are locally identified through the sedimentary layers and interpreted as inter-bedded volcanic sills. Furthermore, from the NNV to the MFZ, the underlying sequence is formed of a 3.0–3.5 km thick volcano-sedimentary sequence presenting important lateral changes in its seismic signature and characterized by a large velocity range (4.4 to 5.8 km/s), which partly reflects variations in the volcanic/sedimentary ratio laterally and with depth. At depth, an initially smoother and reduced eastward thinning of the crust occurs to the West below the continental shelf, from 34 to 31 km thick. The crustal thickness remains relatively constant of about 28–29 km along the Central Domain (CD), whereas a second and major region of thinning (26 to 12 km thick) is imaged West of the MFZ, in the southward prolongation of the Limpopo Corridor (LC). By contrast, as the eastern extremity, the crust is <10 km thick when reaching the MB. Crustal velocities reveal low velocity gradients, with atypical high velocities, increasing to 7.3 to 7.6 km/s at the base of the crust, and globally in the whole crust in the LC, just West of the MFZ. We interpreted the velocity architecture combined with the evidence of volcanism at shallower depths as indicative of an intensively intruded continental crust in the NNV, and discuss the particular segmentation of the longest profile (MZ1) in the kinematic context of both divergent and strike-slipe segments offshore Mozambique. Combining wide-angle and reflection seismic observations along these two profiles and the other MOZ3/5 lines, the data shows a coherent segmentation of the E -W crustal architecture off South Mozambique. These results along MZ1 and MZ2 profiles, combined with the previously published profiles, gives a 3D-view of the NNV, which becomes one of the most passive margins covered in the world by deep wide-angle seismic data. • The basement of North Natal Valley is of continental nature. • The E-W crustal segmentation off South Mozambique images 2 areas of thinning: the main one occured in the Limpopo Corridor. • Our reconstruction and results coincide with the expectations of the geologists of the pan-African East Gondwana. [ABSTRACT FROM AUTHOR]

The Turkana Depression in Eastern Africa separates the elevated plateaus of East Africa to the south and Ethiopia-Yemen to the north. It remains unclear whether the Depression lacks dynamic mantle support, or if the entire East Africa region is dynamically supported and the Depression compensated isostatically by thinned crust. Also poorly understood is how Miocene-Recent extension has developed across the Depression, connecting spatially separated magmatic rift zones in Ethiopia and Kenya. Receiver function analysis is used to constrain Moho depth and bulk-crustal V P / V S ratio below new seismograph networks in the Depression, and on the northern Tanzania craton. Crustal thickness is ∼40 km below northern Uganda and 30–35 km below southern Ethiopia, but 20–30 km below most of the Depression, where mass-balance calculations reveal low elevations can be explained adequately by crustal thinning alone. Despite the fact that magmatism has occurred for 45 Ma across the Depression, more than 15 Ma before East African Rift (EAR) extension initiated, bulk crustal V P / V S across southern Ethiopia and the Turkana Depression (∼1.74) is similar to that observed in areas unaffected by Cenozoic rifting and magmatism. Evidence for voluminous lower crustal intrusions and/or melt, widespread below the Ethiopian rift and Ethiopian plateau to the north, is therefore lacking. These observations, when reviewed in light of high stretching factors (β ≤ 2.11), suggest Cenozoic extension has been dominated until recently by faulting and plate stretching, rather than magma intrusion, which is likely an incipient process, operating directly below seismically-active Lake Turkana. Early-stage EAR basins to the west of Lake Turkana, with associated stretching factors of β ≈ 2 , formed in crust only moderately thinned during earlier rifting episodes. Conversely, ∼23 km-thick crust beneath the Kino Sogo Fault Belt (KSFB) has small offset faults and thin sedimentary strata, suggesting almost all of the observed stretching occurred in Mesozoic times. Despite the KSFB marking the shortest path between focused extensional zones to the north and south, seismicity and GPS data show that modern extension is localized below Lake Turkana to the west. Failed Mesozoic rift zones, now characterized by thinned crust and relatively refractory mantle lithosphere, are being circumnavigated, not exploited by EAR rifting. • Receiver function constraints on Moho depth and V P / V S from the Turkana Depression. • Depression crust 20–30 km thick; bulk crustal V P / V S ratios generally low (≤1.75). • Thin crust explains Depression's low elevation, not a lack of dynamic mantle support. • Past and present magma-assisted rifting not well established below the Depression. • Failed Anza rift is circumnavigated, not exploited, by subsequent East African Rifting. [ABSTRACT FROM AUTHOR]

Twelve combined wide-angle refraction and coincident multi-channel seismic profiles were acquired in the Jequitinhonha-Camamu-Almada, Jacuípe, and Sergipe-Alagoas basins, NE Brazil, during the SALSA experiment in 2014. Profiles SL11 and SL12 image the Jequitinhonha basin, perpendicularly to the coast, with 15 and 11 four-channel ocean-bottom seismometers, respectively. Profile SL10 runs parallel to the coast, crossing profiles SL11 and SL12, imaging the proximal Jequitinhonha and Almada basins with 17 ocean-bottom seismometers. Forward modelling, combined with pre-stack depth migration to increase the horizontal resolution of the velocity models, indicates that sediment thickness varies between 3.3 km and 6.2 km in the distal basin. Crustal thickness at the western edge of the profiles is of around 20 km, with velocity gradients indicating a continental origin. It decreases to less than 5 km in the distal basin, with high seismic velocities and gradients, not compatible with normal oceanic crust nor exhumed upper mantle. Typical oceanic crust is never imaged along these about 200 km-long profiles and we propose that the transitional crust in the Jequitinhonha basin is a made of exhumed lower continental crust. [ABSTRACT FROM AUTHOR]

The high luminosity requirement for a future linear collider sets a demanding limit on the beam quality at the Interaction Point (IP). One potential source of luminosity loss is the motion of the ground itself. The resulting misalignments of the quadrupole magnets cause distortions to the beam orbit and hence an increase in the beam emittance. This paper describes a technique for compensating this orbit distortion by using seismometers to monitor the misalignment of the quadrupole magnets in real-time. The first demonstration of the technique was achieved at the Accelerator Test Facility (ATF) at KEK in Japan. The feed-forward system consisted of a seismometer-based quadrupole motion monitoring system, an FPGA-based feed-forward processor and a stripline kicker plus associated electronics. Through the application of a kick calculated from the position of a single quadruple, the system was able to remove about 80% of the component of the beam jitter that was correlated to the motion of the quadrupole. As a significant fraction of the orbit jitter in the ATF final focus is due to sources other than quadrupole misalignment, this amounted to an approximately 15% reduction in the absolute beam jitter. [ABSTRACT FROM AUTHOR]

Mount St. Helens has been closely monitored by a permanent network including 16 seismometers located within a 15 km radius, yet some of its diverse seismic signals remain challenging to detect and relate to deformation processes. Data from a dense array of 904 geophones within 15 km of Mount St. Helens provide novel constraints on weak seismic signals observed during a two-week deployment in 2014. Here we report on the identification of weak low-frequency (LF) events that were either not detected by the permanent network or were misclassified as likely rockfalls. We refer to the signals as LF earthquakes because they have less power above ~10 Hz and longer durations compared to similar magnitude volcano-tectonic (VT) events. Reverse-time imaging with the entire geophone array indicates that the LF hypocenters overlap with the frequent VT seismicity in a sub-vertical column beneath the summit crater at ≤6 km below sea level. Beamforming of P-wave arrivals with an exceptionally dense sub-array yields slowness estimates that confirm a subsurface origin for 16 LF events. Occurrence of VT and LF events in approximately the same volume suggests distinct source processes rather than path effects as the primary explanation for their different signals. Some of the LF and VT events have multiple spectral peaks that may be consistent with source mechanisms involving resonance in fluid-filled cavities. However, the majority of LF and VT event spectra exhibit smooth amplitude decay with increasing frequency, consistent with shear failure sources. The depletion of high frequencies for LF events could be caused by unusually low rupture velocities or stress drops. Our results indicate a variety of earthquake source processes occur in a sub-vertical column at ≤6 km depth, which is thought to overly the primary upper crustal magma reservoir. LF events are typically associated with eruptive or near-eruptive activity and are generally not reported at depths greater than ~1 km at Mount St. Helens, but based on our short-duration high-density experiment we suggest that upper crustal LF events may be more common than previously recognized and occur across a broader depth range. [ABSTRACT FROM AUTHOR]

Seasonal variations in the seismicity of volcanic and geothermal reservoirs are usually attributed to the hydrological cycle. Here, we focus on the Aluto-Langano geothermal system, Ethiopia, where the climate is monsoonal and there is abundant shallow seismicity. We deployed temporary networks of seismometers and GPS receivers to understand the drivers of unrest. First, we show that a statistically significant peak in seismicity occurred 2–3 months after the main rainy season, with a second, smaller peak of variable timing. Seasonal seismicity is commonly attributed to variations in either surface loading or reservoir pore pressure. As loading will cause subsidence and overpressure will cause uplift, comparing seismicity rates with continuous GPS, enables us to distinguish between mechanisms. At Aluto, the major peak in seismicity is coincident with the high stand of nearby lakes and maximum subsidence, indicating that it is driven by surface loading. The magnitude of loading is insufficient to trigger widespread crustal seismicity but the geothermal reservoir at Aluto is likely sensitive to small perturbations in the stress field. Thus we demonstrate that monsoonal loading can produce seismicity in geothermal reservoirs, and the likelihood of both triggered and induced seismicity varies seasonally. [ABSTRACT FROM AUTHOR]

Using recordings of earthquakes on Oceanic Bottom Seismographs and onshore stations on the coastal margins of Colombia, Panama, and Ecuador, we estimate attenuation parameters in the upper lithosphere of the Panama Basin. The tomographic images of the derived coda-Q values are correlated with estimates of Curie Point Depth and measured and theoretical heat flow. Our study reveals three tectonic domains where magmatic/hydrothermal activity or lateral variations of the lithologic composition in the upper lithosphere can account for the modeled thermal structure and the anelasticity. We find that the Costa Rica Ridge and the Panama Fracture Zone are significant tectonic features probably related to thermal anomalies detected in the study area. We interpret a large and deep intrinsic attenuation anomaly as related to the heat source at the Costa Rica Ridge and show how interactions with regional fault systems cause contrasting attenuation anomalies. [ABSTRACT FROM AUTHOR]

Processed accelerograms define the ground motion input for a variety of engineering and scientific analyses. The M w 7.8 Gorkha, Nepal earthquake of 25 April 2015 currently has data from six near-field seismograph stations, recorded from within Nepal, available in the public domain. However, only the USGS sensor from the Kantipath (KATNP) station in Kathmandu has a processed data set available. The remaining acceleration time series are only provided in raw form, which require additional signal processing to be properly utilized for analysis. This paper discusses three different processing schemes for the accelerograms that may be used based on the intended application. Based on these processed records, some observations of the ground motions are then discussed. Fourier and response spectra results are presented to illustrate the effects of the processing procedure and the frequency contents. The processed ground motions are compared to applicable ground motion prediction equations (GMPEs) for peak ground acceleration (PGA) and velocity (PGV). It is shown that existing GMPEs generally overestimate the PGA and PGV. Due to the presence of long period pulse-like behavior in the time series, two pulse extraction models are used to estimate the pulse parameters, including the pulse period (T P ). By comparing the pulse period to an M W –T P relationship from the literature, it is shown that the recording from the rock site is an excellent match, while the other five soil sites have shorter periods than predicted. The M W -T P relationship shows longer pulse periods in rock sites than soil sites for magnitudes greater than M W 7.8, which is also observed from the results of this study. The observed long period peaks in the response spectra are attributed mainly to directivity effects. [ABSTRACT FROM AUTHOR]

This study shows a formulation that allows obtaining theoretical results that show the energy contents associated with the propagation of compressional and shear seismic waves (P- and S-waves respectively) for the case of a two-dimensional medium. During the propagation of seismic waves, the energy contents of P- and S-waves show fixed proportions according to the properties of the medium where they propagate (i.e. density, wave propagation velocity and Poisson ratio). Theoretically, a material with a Poisson ratio of 0.35 implies that P-waves will only represent 18.75% of the total energy while the other 81.25% will be contributed by S-waves. For a Poisson ratio of 0.45, S-waves will be enormously powerful and contribute with 91.67% of the total energy during propagation. On the other hand, it is also possible to obtain the energy contents through correlations of seismic motions by means of the interpretation of recovered seismograms. In this study, it is also shown that under certain conditions, the recovered energy converges to exact solutions. Our results are validated using published solutions showing an excellent agreement. In addition, theoretical examples have been developed simulating seismic noise and it has been found that energy contents of the P- and S-waves are also satisfied. [ABSTRACT FROM AUTHOR]