Search

Coseismic slip on the Patton Bay splay fault system during the 1964 Mw 9.2 Great Alaska Earthquake contributed to local tsunami generation and vertically uplifted shorelines as much as 11 m on Montague Island in Prince William Sound (PWS). Sudden uplift of 3.7–4.3 m caused coastal lagoons along the island's northwestern coast to gradually drain. The resulting change in depositional environment from marine lagoon to freshwater muskeg created a sharp, laterally continuous stratigraphic contact between silt and overlying peat. Here, we characterize the geomorphology, sedimentology, and diatom ecology across the 1964 earthquake contact and three similar prehistoric contacts within the stratigraphy of the Hidden Lagoons locality. We find that the contacts signal instances of abrupt coastal uplift that, within error, overlap the timing of independently constrained megathrust earthquakes in PWS—1964 Common Era, 760–870 yr BP, 2500–2700 yr BP, and 4120–4500 yr BP. Changes in fossil diatom assemblages across the inferred prehistoric earthquake contacts reflect ecological shifts consistent with repeated draining of a lagoon system caused by >3 m of coseismic uplift. Our observations provide evidence for four instances of combined megathrust‐splay fault ruptures that have occurred in the past ∼4,200 years in PWS. The possibility that 1964‐style combined megathrust‐splay fault ruptures may have repeated in the past warrants their consideration in future seismic and tsunami hazards assessments. Plain Language Summary: During the Mw 9.2 1964 Great Alaska Earthquake, both the subduction zone and the crustal faults connected to the subduction zone (called splay faults) slipped, lifting shorelines up to 11 m on Montague Island in Prince William Sound (PWS) and contributing to local tsunami generation. The sudden uplift cut off tidal connection to coastal lagoons on Montague Island's northwest coast, producing a change to a drier, freshwater environment. The sudden environmental change created a clear sedimentary change from pre‐earthquake lagoon silt to post‐earthquake rooted soil in the stratigraphy of a study site known as Hidden Lagoons. Using the stratigraphic evidence of the 1964 uplift as a guide, we investigated deeper into the subsurface of Hidden Lagoons to see if there were previous instances of subduction zone and splay fault activation. We discovered three previous stratigraphic boundaries marking times when earthquakes uplifted the land. Changes in the species of diatoms across these boundaries show that the marine lagoon system was repeatedly drained by earthquakes causing over 3 m of uplift. These uplift events match the timing of four of the eight known prehistoric subduction zone earthquakes in PWS, suggesting that splay faults have slipped with the subduction zone multiple times over the past ∼4,200 years. Key Points: We find widespread stratigraphic evidence for the 1964 M9.2 earthquake and three prehistoric earthquake contacts on Montague Island, AlaskaStratigraphic and diatom analyses suggest ruptures of splay faults may have occurred in conjunction with 4 of 8 documented Alaska‐Aleutian subduction zone earthquakesHazard assessments may want to consider the tsunami potential with possible future 1964‐style combined megathrust‐splay fault ruptures [ABSTRACT FROM AUTHOR]

The article focuses on synthesizing research on the seismotectonics of the San Andreas Fault System within the San Gorgonio Pass region of Southern California. It explores the complex fault geometry, slip distribution, and seismic hazard implications through multidisciplinary studies, including geology, geophysics, and modeling. It aims to enhance understanding of fault behavior and earthquake risk assessment, serving as a model for studying restraining bends in strike-slip faults globally.

Large block‐bounding faults on the Tibetan plateau are significant geological structures that accommodate tectonic movements and accumulate stress, leading to large earthquakes. Quantifying the interseismic slip deficit rate helps to better assess the earthquake potential. We combine available InSAR (2015–2020) and interseismic GPS data to determine fault coupling along 14 major block‐bounding faults. Spatially dense InSAR measurements remarkably improve the resolution of the coupling model. Combined with a GPS‐constrained block model, we examine the performance of the inversion approach with the stress constraint and the common Laplacian smoothing based on both synthetic tests and real data. We suggest that, for continental strike‐slip faults, adding the stress constraint can mitigate unphysical coupling distributions due to unreasonable assumptions or modeling artifacts, reducing the model uncertainty and improving the accuracy of the coupling model. This is particularly useful for segments featured by a highly heterogeneous distribution of coupling along the transition zone from locking to creeping region, partially‐coupling segment, and junction zone between main and subsidiary faults. We present a large‐scale fault coupling map along the major block‐bounding faults on the northeastern and eastern Tibetan plateau, highlighting the distinct degrees of fault coupling and lateral variations. The collage of coupling maps along different faults demonstrates the kinematic features over a broad time scale during earthquake cycles ranging from early to late interseismic phases, such as the segments ruptured during the 2001 Kokoxili earthquake and the 1920 Haiyuan earthquake. Plain Language Summary: Large faults at the boundary of blocks accommodate a significant portion of the relative movement between adjacent blocks and accumulate tectonic stress during the interseismic period. Consequently, these faults have a high potential to generate large earthquakes. To evaluate the distribution of strain accumulation, we analyze InSAR (2015–2020) and interseismic GPS measurements to construct a coupling model, which tells us the extent to which two blocks are locked together and accumulate stress before the next earthquake. We focus on 14 major faults on the eastern and northeastern Tibetan plateau. The addition of the spatially dense InSAR data helps to resolve the coupling distribution in greater detail, where GPS observations are limited. We evaluate different approaches to determine fault coupling, including stress constraints and smoothing techniques. Our findings indicate that adding a stress constraint performs better than the smoothing operator and helps mitigate physically unrealistic coupling distributions in the inversion using the spatial smoothing method. The stress constraint improves the accuracy of the coupling model. Based on the stress‐constrained inversion, we present a comprehensive fault coupling map in the northeastern and eastern Tibetan plateau, highlighting the spatial variations of fault coupling, which can be used in earthquake hazard assessment. Key Points: Stress constraints can mitigate unphysical coupling distributions and reduce the uncertainty of the coupling model for continental faultsWe highlight the improvement when using stress constraints in the case of sharp coupling contrasts along the strike‐slip faultWe provide a new coupling model along 14 major block‐bounding faults on the eastern and northeastern Tibetan plateau [ABSTRACT FROM AUTHOR]

The northeastern margin of the Tibetan Plateau (NE Tibetan Plateau) exhibits active geological structures and has experienced multiple strong earthquakes, with M ≥ 7, throughout history. Particularly noteworthy is the 1920 M81/2 earthquake in the Haiyuan region that occurred a century ago and is documented as one of the deadliest earthquakes. Consequently, analyzing seismic risks in the northeastern margin of the Tibetan Plateau holds significant importance. The b value, a crucial parameter for seismic activity, plays a pivotal role in seismic hazard analyses. This study calculates the spatial b values in this region based on earthquake catalogs since 1970. The study area encompasses several major active faults, and due to variations in b values across different fault types, traditional grid-search methods may introduce significant errors in calculating the spatial b value within complex fault systems. To address this, we employed the hierarchical space–time point–process (HIST-PPM) method proposed by Ogata. This method avoids partitioning earthquake samples, optimizes parameters using Akaike's Bayesian Information Criterion (ABIC) with entropy maximization, and theoretically allows for a higher spatial resolution and more accurate b value calculations. The results indicate a high spatial heterogeneity in b values within the study area. The northwestern and southeastern regions exhibit higher b values. Along the Haiyuan fault zone, the central rupture zone of the Haiyuan earthquake has relatively higher b values than other regions of this fault zone, which is possibly related to the sufficient release of stress during the main rupture of the Haiyuan earthquake. The b values vary from high in the west to low in the east along the Zhongwei fault. On the West Qinling fault zone, the epicenter of the recent Minxian–Zhangxian earthquake is associated with a low b value. In general, regions with low b values correspond well to areas with moderate–strong seismic events in the past 50 years. The spatial differences in b values may reflect variances in seismic hazards among fault zones and regions within the same fault zone. [ABSTRACT FROM AUTHOR]

The significant Shillong earthquake of 1897 in the western part of the Shillong Massif profoundly impacted the entire Northeast India region, resulting in extensive devastation at both surface and subsurface levels. Numerous land fissures, sand veins, swampy areas, and land tilting and upliftment were formed during the earthquake in the western part of the Shillong plateau. This study adopts an integrated approach, combining seismic, geophysical, and fluvial geomorphology methods, to quantify the co-seismic subsurface rupture. Multichannel Surface Wave Analyzer (MASW) and resistivity surveys are conducted at fourteen locations along three profiles crossing the Krishnai and Chedrang Rivers in the Chedrang valley. In certain specified locations, significant surface rupture is observed, and the co-seismic surface uplift is measured to be 5 + 1 m on vertical planes at the western end of the rupture of the Oldham fault. The shear wave velocities along the profiles range from 184 to 466 m/s, indicating a platform for intense shallow seismicity triggered by fracture. The region experiences intense seismic activity, with the bottom of the seismogenic zone estimated to be 40 km, mainly dominated by thrust with strike-slip components. The local stress pattern in the Chedrang valley, oriented NE-SW, differs from the regional stress pattern, NNW-SSE, indicating the influence of geodynamic controls. Fluvial-morphometric measurements of the Krishnai and Chedrang Rivers for six different stretches in each case during 1964, 1991, and 2014 reveal a westward shifting of the Krishnai River ranging from 190 to 269 m, while the Chedrang River exhibits variable south-westward avulsion along these stretches, shifting approximately 132–312 m. Detailed fluvial morphological mapping highlights a key site where the stratigraphy of the fault scarp, reaching a height of 13ft, indicates the presence of modern channels, colluviums, gravel, and pebble beds with sand lenses, representing a portion of a mega thrust event. Simultaneously, high-resolution topographic profiles are analyzed using Total Station (GPS based) to observe co-seismic surface uplifts induced by the 1897 earthquake. The simplest deformation model suggests that a majority of the intra-seismic elastic loading east of the Krishnai and Chedrang rivers was uplifted during the 1897 earthquake due to co-seismic and post-seismic rupture, primarily in the western part of the Shillong plateau beneath the Chedrang valley. This energy transfer affected the north–south direction of the Krishnai valley, where the Krishnai river and the 'Mori' (dead) Krishnai river exist, as evidenced by subsurface deformation and subsequent avulsion of the Krishnai river. The parameters investigated in this study contribute to a better understanding of the geodynamics and seismic hazard assessment of the region, providing valuable insights into the consequences of the 1897 earthquake and its implications for future seismic events. [ABSTRACT FROM AUTHOR]

The neotectonic processes are crucial for identification of active faults in a seismic unstable area. The Aїn Smara active fault runs along the Middle Rhumel Valley located in Constantine area of Algerian Eastern Tell Atlas mountain chain and it emerges in the south‒western part of the epicentral zone of the earthquake occurred on October 27, 1985 (Mw = 5.8) within a corridor displaying morphological features and deformed Pliocene‒Quaternary layers, which are the consequence of transpressive tectonic regime. In our study the morpho-tectonic and structural research supported by the fieldwork, was performed. The thick fault gouge indicating simple shear deformation, fault breccias and minor faults affecting the Pliocene limestone and Quaternary alluvial terraces, were found. The active fault splits into northern and southern segments. The northern segment corresponds to the El Aria Fault that ruptured during the earthquake in 1985 and the southern segment with the studied Aĭn Smara Fault. Our research showed the significant extent of the active fault and including its parameters for improved seismic hazard assessment of the Constantine area. [ABSTRACT FROM AUTHOR]

The seismogenesis of rocks is mainly affected by their mineral composition and in situ conditions (temperature and state of stress). Diverse laboratory experiments have explored the frictional behaviour of the rocks and rock-forming minerals most common in the crust and uppermost mantle. However, it is debated how to "upscale" these results to the lithosphere. In particular, most earthquakes in the crust nucleate down to the crustal seismogenic depth (CSD), which is a proxy for the maximum depth of crustal earthquake ruptures in seismic hazard assessments. In this study we propose a workflow to upscale and validate those laboratory experiments to natural geological conditions relevant for crustal and upper-mantle rocks. We used the southern Caribbean and northwestern South America as a case study to explore the three-dimensional spatial variation of the CSD (mapped as D90, the 90 % percentile of hypocentral depths) and the temperatures at which crustal earthquakes likely occur. A 3D steady-state thermal field was computed for the region with a finite-element scheme using the software GOLEM, considering the uppermost 75 km of a previously published 3D data-integrative lithospheric configuration, lithology-constrained thermal parameters, and appropriate upper and lower boundary conditions. The model was validated using additional, independent measurements of downhole temperatures and heat flow. We found that the majority of crustal earthquakes nucleate at temperatures less than 350 ∘ C, in agreement with frictional experiments of typical crustal rocks. A few outliers with larger hypocentral temperatures evidence nucleation conditions consistent with the seismogenic window of olivine-rich rocks, and can be due to either uncertainties in the Moho depths and/or in the earthquake hypocentres or the presence of ultramafic rocks within different crustal blocks and allochthonous terranes accreted to this complex margin. Moreover, the spatial distribution of crustal seismicity in the region correlates with the geothermal gradient, with no crustal earthquakes occurring in domains with low thermal gradient. Finally, we find that the largest earthquake recorded in the region (Mw=7.1 , Murindó sequence, in 1992) nucleated close to the CSD, highlighting the importance of considering this lower-stability transition for seismogenesis when characterizing the depth of seismogenic sources in hazard assessments. The approach presented in this study goes beyond a statistical approach in that the local heterogeneity of physical properties is considered in our simulations and additionally validated by the observed depth distribution of earthquakes. The coherence of the calculated hypocentral temperatures with those expected from laboratory measurements provides additional support to our modelling workflow. This approach can be applied to other tectonic settings worldwide, and it could be further refined as new, high-quality hypocentral locations and heat flow and temperature observations become available. [ABSTRACT FROM AUTHOR]

We conducted a study on the Aceh Fault, an active right-lateral strike-slip fault in northern Sumatra, Indonesia. Despite its seismic hazard potential, the slip characteristics of this fault are not well-understood. Using a combination of remote sensing and field methods, we mapped the distribution of displacement recorded by offset channels along the fault. Our goal is to identify evidence of past surface rupture, characterize their tectonic geomorphology setting, and assess their potentials as slip-rate and paleoseismic sites. The documented right-lateral displacements of channels and ridges from 35 observation points are mostly in the order of magnitude of hundreds of meters, with only a few sites exhibiting meter-scale measurable offsets. Our results provide important first-order data that can be used to locate sites suitable for paleoseismic trenching or offset investigations. This information will support the development of a maximum magnitude and earthquake recurrence model of the fault, which are crucial for seismic hazard analysis in the region. [ABSTRACT FROM AUTHOR]

On February 6, 2023, a magnitude 7.8 earthquake and subsequent strong seismic activity struck in Kahramanmaras region, causing over 50,000 deaths in Turkey and Syria. The earthquake resulted in a surface rupture of the East Anatolian Fault Zone (EAFZ) spanning approximately 300 km. To gain new insights into the neotectonic and current stress field in the region, we compiled 141 focal mechanism solutions (FMS) of earthquakes (with magnitude M ≥ 3) that occurred along the EAFZ between 05/01/2003 and 27/02/2023. Stress inversion, by using the Win-Tensor program, indicated a predominant strike-slip tectonic regime, with few normal and thrust events related to complex fault geometry along the principal displacement zone. The calculated pressure/tension axes in the first order stress field are mainly sub-horizontal, with a maximum horizontal compressive stress (SHmax) direction of N19 ± 9.9° E, which aligns well with the slip character of the EAFZ. To reconstruct the second and third order stress fields, the study area was subdivided into five zones based on their structures and geomorphological characteristics. Reduced stress tensors were obtained for each zone, indicating a small rotation of SHmax directions under a prevailing strike-slip faulting regime. The maximum (σ1) and minimum (σ3) stress axes are nearly horizontal; while the intermediate (σ2) stress axis is nearly vertical, consistent with a predominant strike-slip regime. The results show, also, that the Kahramanmaras earthquake was caused by the neotectonic reactivation of northeast-striking sinistral strike-slip fault, with a north–south-oriented maximum horizontal stress axis. The neotectonic activity along the EAFZ aligns well with the collision models between the Arabian and Eurasian plates. Finally, a detailed seismic hazard assessment is required for the EAFZ and nearby regions. [ABSTRACT FROM AUTHOR]

This study aims to investigate the potential of GNSS data in earthquake zoning and risk assessment in a seismically active region. The study area is located in Uzbekistan, where the interaction of several tectonic plates results in frequent earthquakes. The study focused on two periods from October to October of the next year, respectively, for 2018 and 2019, 2019 and 2020 to analyze GNSS velocities and earthquake zoning maps to identify areas at high risk of seismic activity. The study also utilized GIS and spline interpolation to create continuous surface maps of risk zones based on earthquake hazard data. The results showed that the entire study area is at high seismic risk, with a tendency for rotational movement in the zone of intersection of tectonic plates. Velocities range from 1.56-20.3 mm/yr and 1.64-14 mm/yr for the two periods. Moreover, the analysis of vertical earth surface displacements indicates a tendency towards soil subsidence in the western part and uplift in the northeastern part of the study area. The study concludes that GNSS analysis can provide valuable insights into seismic hazard assessment and improve our understanding of the tectonic processes leading to earthquakes. [ABSTRACT FROM AUTHOR]

Variations in fault zone maturity have intermittently been invoked to explain variations in some seismological observations for large earthquakes. However, the lack of a unified geological definition of fault maturity makes quantitative assessment of its importance difficult. We evaluate the degree of empirical correlation between geological and geometric measurements commonly invoked as indicative of fault zone maturity and remotely measured seismological source parameters of 34 MW ≥ 6.0 shallow strike‐slip events. Metrics based on surface rupture segmentation, such as number of segments and surface rupture azimuth changes, correlate best with seismic source attributes while the correlations with cumulative fault slip are weaker. Average rupture velocity shows the strongest correlation with metrics of maturity, followed by relative aftershock productivity. Mature faults have relatively lower aftershock productivity and higher rupture velocity. A more complex relation is found with moment‐scaled radiated energy. There appears to be distinct behavior of very immature events which radiate modest seismic energy, while intermediate mature faults have events with higher moment‐scaled radiated energy and very mature faults with increasing cumulative slip tend to have events with reduced moment‐scaled radiated energy. These empirical comparisons establish that there are relationships between remote seismological observations and fault system maturity that can help to understand variations in seismic hazard among different fault environments and to assess the relative maturity of inaccessible or blind fault systems for which direct observations of maturity are very limited. Plain Language Summary: Earthquakes occur on faults, which are often complex structures. The relationship between the structure of faults and the seismological aspects of an earthquake rupturing that fault is an ongoing puzzle. Here we empirically compare geological and geometrical aspects of strike‐slip fault zones and surface ruptures of major events with seismological attributes of the events. We consider factors such as the total offset on the fault that has accumulated over geological time and the number of segments in maps of earthquake rupture and investigate how they correlate with aspects of the resulting earthquake such as the number of aftershocks or the rupture speed. Several of these factors co‐evolve as a fault accumulates slip and matures, thus the trends can be interpreted as indicative of the type of earthquakes observed on mature versus immature faults. We find that less mature faults tend to generate more aftershocks and have lower rupture velocity. Energy estimated from seismograms is relatively low for very immature faults, increases with fault evolution and then decreases as maturity further increases. These relationships help elucidate seismic hazard for fault systems of different maturity and delineate the important fault zone factors that have bearing on earthquake rupture and aftershock generation process. Key Points: Strike‐slip fault zone relative maturity is inferred from cumulative fault slip and from individual event surface rupture segment geometryMaturity measures are compared with relative aftershock productivity, rupture velocity, and moment‐scaled radiated energyLess mature faults have higher relative aftershock productivity and lower rupture velocity than mature faults [ABSTRACT FROM AUTHOR]

Neotectonic activity in the western margin of the Sierra Madre Oriental in northeastern Mexico was evaluated using geomorphological, geological, structural, and seismological analyses. We evaluated recent tectonic evidence in the basin of the Potosí Valley related to the Santo Domingo Fault System (SDFS), which is one of the largest active extensional fault zones documented so far in the transition zone between the Basin and Range and the Sierra Madre Oriental provinces. Two indices were used in the geomorphological analysis: transverse topographic basin asymmetry (T) and mountain front sinuosity (Smf). The results show that the studied basin is slightly tilted to the WSW, consistent with the typical basin deformation pattern in the Basin and Range province. Structural data collected in the field unveil a NW–SE striking fault system, geometrically and kinematically similar to the Cenozoic lineaments of the Basin and Range province. The local stress tensor calculated in this study indicates an extensional tectonic regime, suggesting S V > S NW > S NE . Analysis defines an azimuth trend of 298° and 036° for σ 2 (S Hmax) and σ 3 S hmin , respectively. According to the results, the SDFS is well orientated for possible future reactivation as a normal fault system. We estimate that a segmented rupture of the SDFS could produce seismic events on the order of magnitude 5 < Mw < 6. Considering a continuous rupture (~ 42 km) of the SDFS in a single event, an earthquake of Mw 7.0 could be expected. The results are essential to estimate seismic hazards in northeastern Mexico, including important urban areas, such as Monterrey, Nuevo León, and Saltillo, Coahuila. [ABSTRACT FROM AUTHOR]

The San Gabriel, Chino, and San Bernardino sedimentary basins in Southern California amplify earthquake ground motions and prolong the duration of shaking due to the basins' shape and low seismic velocities. In the event of a major earthquake rupture along the southern segment of the San Andreas fault, their connection and physical proximity to Los Angeles (LA) can produce a waveguide effect and amplify strong ground motions. Improved estimates of the shape and depth of the sediment‐basement interface are needed for more accurate ground‐shaking models. We obtain a three‐dimensional basement map of the basins by integrating gravity and seismic measurements. The travel time of the sediment‐basement P‐to‐S conversion, and the Bouguer gravity along 10 seismic lines, are combined to produce a linear relationship that is used to extend the 2D profiles to a 3D basin map. Basement depth is calculated using the predicted travel time constrained by gravity with an S‐wave velocity model of the area. The model is further constrained by the basement depths from 17 boreholes. The basement map shows the south‐central part of the San Gabriel basin is the deepest part and a significant gravity signature is associated with our interpretation of the Raymond fault. The Chino basin deepens toward the south and shallows northeastward. The San Bernardino basin deepens eastward along the edge of the San Jacinto Fault Zone. In addition, we demonstrate the benefit of using gravity data to aid in the interpretation of the sediment‐basement interface in receiver functions. Plain Language Summary: The shaking levels in the Los Angeles (LA) metropolitan area due to an earthquake on the San Andreas fault are underestimated. Northeast of LA, the San Gabriel, Chino, and San Bernardino basins influence the amount of shaking the LA area will experience. Sedimentary basins like these can amplify and trap seismic waves. Understanding these basins' shapes will improve our Earth model of the area and therefore seismic hazard estimates. The Basin Amplification Seismic Investigation project installed several small seismic instruments across these basins to characterize the structure of the basins. Along with gravity measurements, which capture information about the rock's density variations, we determine the basins' depth and shape. The depth model is then combined with a new velocity model of the area to produce an improved Earth model. Future studies of ground shaking should take these improved models into account. Key Points: Passive seismic and gravity measurements are integrated to estimate the 3D depth of the northern Los Angeles basinsThe maximum depth in the San Gabriel basin is ∼4.5 km, and Chino and San Bernardino basins are less than 2 km deepThe use of gravity helps to delineate faults across the basin, which helps our sediment‐basement interpretation in the receiver functions [ABSTRACT FROM AUTHOR]

This document is a compilation of various research papers and abstracts related to seismic activity and earthquake research in Croatia and Hungary. The papers cover topics such as seismic site amplification, site response analysis, local site effects, lithosphere structure, gravity anomaly models, and seismic performance assessment of buildings. The research provides valuable insights into earthquake risk and mitigation strategies in the region. The document also includes links to additional information and resources for further exploration. [Extracted from the article]

Historical and instrumental earthquake catalogs in low strain rate regions are not necessarily indicative of the long-term spatio-temporal distribution of seismicity. This implies that probabilistic seismic hazard analysis (PSHA) should also consider geologic and geodetic data through fault-based seismogenic sources. However, it is not always clear how on-fault magnitude-frequency distributions (MFDs) should be described and, if the seismogenic layer is especially thick, how fault sources should be extrapolated down-dip. We explore these issues in the context of a new PSHA for Malawi, where regional extensional rates are 0.5–2 mm yr−1, the seismogenic layer is 30–40-km thick, the instrumental catalog is ∼60 yr long and fault-based sources were recently collated in the Malawi Seismogenic Source Model. Furthermore, Malawi is one of several countries along the East African Rift where exposure to seismic hazard is growing, but PSHA does not typically consider fault sources. We use stochastic event catalogs to explore different fault source down-dip extents and MFDs. Our PSHA indicates that hazard levels are highest for a Gutenberg–Richter on-fault MFD, even at low probabilities of exceedance (2 per cent in 50 yr), whilst seismic hazard levels are also sensitive to how relatively short (<50 km) fault sources are extrapolated down-dip. For sites close to fault sources (<40 km), seismic hazard levels are doubled compared to previous instrumental-seismicity based PSHA in Malawi. Cumulatively, these results highlight the need for careful fault source modelling in PSHA of low strain rate regions and the need for new fault-based PSHA elsewhere in the East Africa Rift. [ABSTRACT FROM AUTHOR]

We summarise the geological setting of complex surface rupture of the 2016 Mw 7.8 Kaikōura earthquake in the Marlborough Tectonic Domain of New Zealand. The event was complex both seismologically and geologically but not totally dissimilar to other large historical events globally. The earthquake occurred in the comprehensively imbricated, steeply-dipping Pahau Terrane crust that exhibits numerous tectonic overprints with diverse faulting styles. The current strike slip faults of the Marlborough Fault System are immature in their structural development and occupy, at least in part, inherited faults of earlier deformation phases. Several of the faults that ruptured in 2016 may connect at seismogenic depths. A listric fault geometry is likely for many of the faults that ruptured in 2016. This interpretation is supported by crustal seismic mapping identifying listric geometries for other large faults within the region. Examination of other historic surface rupturing earthquakes in the Marlborough Tectonic Domain and globally show some complexity but not to the same level of multifault rupture as in 2016. We conclude that multifault ruptures may be enhanced in the Kaikōura region where the Australian plate crust is thinner than farther west and the plate boundary deformation, at rates of >20 mm year-1, transfers between closely-spaced faults with acute changes in surface geometry and with diverse rupture characteristics. The trend in seismic hazard assessment since 2016 is to include multifault ruptures universally, but this would be inconsistent with historic events in the Marlborough Tectonic Domain. Consideration of geological structure and history may usefully be incorporated into seismic hazard methodology to evaluate when and where multifault source models are indeed appropriate. [ABSTRACT FROM AUTHOR]

Interseismic deformation describes the gradual accumulation of crustal strain within the tectonic plate and along the plate boundaries before the sudden release as earthquakes. In this study, we use 5 years of high spatial and temporal geodetic measurements, including Global Navigation Satellite System and Interferometric Synthetic Aperture Radar to monitor 3‐dimension interseismic crustal deformation and horizontal strain rate in Taiwan. We find significant deformation (strain rate >8 × $\times $ 10−6 yr−1) along the plate boundary between the Philippine Sea and the Eurasian Plates in east Taiwan. The high strain rate in the southern part of the Western Foothills is distributed along a few major fault systems, which reveals the geometry of the deformation front in west Taiwan. Our results help identify active faults in southwest and north Taiwan that were not identified before. These findings can be insightful in informing future seismic hazard models. Plain Language Summary: An earthquake cycle includes three phases: interseismic, coseismic, and postseismic. Interseismic deformation refers to the continuous crustal deformation that is built up by active tectonics. Depending on the relative motion between tectonic plates, the earthquake recurrence interval could vary by a few orders between different locations. As a result, knowing the crustal deformation rate and deformation accumulated in different fault zones can be useful for investigating future earthquake hazards. Using space geodesy tools like Global Navigation Satellite System and Interferometric Synthetic Aperture Radar, we can monitor surface deformation during the interseismic period. In this study, we monitor interseismic deformation in Taiwan using geodesy. We find that east Taiwan where two tectonic plates collide has the highest rate of deformation. In southwest and north Taiwan where most of the population resides, there is also high‐level of deformation distributed across a few different faults, indicating that some of the faults have a higher risk generating future earthquakes. As a result, knowing the amount of faults slip and amount of deformation built up during this interseismic period may inform us of potential future earthquake hazards. Key Points: This study combines Interferometric Synthetic Aperture Radar and Global Navigation Satellite System and produces high‐resolution 3‐D interseismic crustal velocities and strain rate estimates in TaiwanStrain rate measurements show high surface strain cumulation along east and southwest TaiwanThe surface strain rates and the earthquake hazard models based on seismology and field study are in good agreement [ABSTRACT FROM AUTHOR]

Seismic hazard assessment in slow straining regions is challenging because earthquake catalogues only record events from approximately the last 100 years, whereas earthquake recurrence times on individual faults can exceed 1000 years. Systematic mapping of active faults allows fault sources to be used within probabilistic seismic hazard assessment, which overcomes the problems of short-term earthquake records. We use Shuttle Radar Topography Mission (SRTM) data to analyse surface deformation in the Luangwa Rift in Zambia and develop the Luangwa Rift Active Fault Database (LRAFD). The LRAFD is an open-source geospatial database containing active fault traces and their attributes and is freely available at 10.5281/zenodo.6513691. We identified 18 faults that display evidence for Quaternary activity, and empirical relationships suggest that these faults could cause earthquakes up to Mw 8.1, which would exceed the magnitude of historically recorded events in southern Africa. On the four most prominent faults, the median height of Quaternary fault scarps varies between 12.9 ± 0.4 and 19.2 ± 0.9 m, which suggests they were formed by multiple earthquakes. Deformation is focused on the edges of the Luangwa Rift: the most prominent Quaternary fault scarps occur along the 207 km long Chipola and 142 km long Molaza faults, which are the rift border faults and the longest faults in the region. We associate the scarp on the Molaza Fault with possible surface ruptures from two 20th century earthquakes. Thus, the LRAFD reveals new insights into active faulting in southern Africa and presents a framework for evaluating future seismic hazard. [ABSTRACT FROM AUTHOR]

Earthquake simulation and hazard prediction are strongly hampered by insufficient physical knowledge of the constitutive behavior of faults. Laboratory studies of carbonate fault friction suggest that seismogenic rupture on faults in carbonate terrains can be explained by a transition from high friction at low initial sliding velocities (V) to low friction at seismic slip velocities, that is, by rapid dynamic weakening. One proposed explanation for this weakening, invokes frictional heating resulting in deformation by grain boundary sliding accommodated by solid‐state diffusion (sometimes referred to as "viscous" or "superplastic" flow). We recently added this dynamic weakening mechanism to a microphysically based model addressing the (rate‐and‐state) frictional behavior of granular gouges undergoing low V shear characteristic of rupture nucleation and arrest. In the present study, we applied the full model to simulate seismic slip in laboratory carbonate faults. Assuming that slip localizes in a principal shear band within the fault (gouge) zone, and accounting for grain size evolution with velocity and temperature, the model reproduces the frictional, thermal and (micro‐)structural evolution observed during seismic slip experiments. In particular, it predicts spatial and temporal evolutions of grain size, porosity, and dominant deformation mechanisms, within and outside the assumed shear band, consistent with trends identified in the laboratory and natural fault zones. Plain Language Summary: Improving the basis for earthquake hazard assessment relies in part on structural observation of natural fault zones, on laboratory experiments, and on theoretical developments. While quantitative models that reproduce the laboratory data on frictional slip on faults is the minimum necessary to simulate their mechanical behavior in nature, convincing models must ultimately also account for all key fault zone observations. Taking a fault in carbonate rock as an example, and using fundamental data on the microscale processes that lead to fault friction, this study takes a first step toward simulating the dynamic evolution and self‐organization of internal fault zone (micro)structure, processes and properties during a seismic slip event. The results show that the model captures many key observations on seismic fault behavior, paving the way for still further improvements in developing a physics‐based understanding of earthquake rupture in future. [ABSTRACT FROM AUTHOR]

The Nanbei River–Boli Fault is one of the largest NW-trending faults in Northeast China. However, limited data on the style and timing of recent earthquake activity on this fault greatly restrict the accuracy of seismic risk assessment. Here, we provide evidence of late Pleistocene to Holocene activity of the eastern segment of this fault for the first time. Specifically, the eastern segment of the Nanbei River–Boli Fault has experienced multiple earthquakes since the late Quaternary. Trench excavations indicate a recent strong earthquake at 7.28–2.11 ka, with approximately 1 m of co-seismic vertical displacement and preliminary estimates of the minimum vertical slip rates of 0.07–0.12 mm/a. According to a comprehensive analysis, we estimate that the eastern segment of the Nanbei River–Boli Fault can generate strong earthquakes of magnitude 7.0. This research provides important information for seismic risk assessments and seismic zoning, which can help seismic hazard assessment and mitigate their effects in Northeast China. • We analyze the Nanbei River–Boli Fault, southern margin of Boli Basin, Northeast China. • Radiocarbon and OSL dating provide the timing of recent strong earthquakes. • We estimate the maximum earthquake magnitude and minimum vertical slip rate. • The fault has experienced multiple surface rupture events in the late Quaternary. • This is the first evidence of late Pleistocene to Holocene activity along the fault. [ABSTRACT FROM AUTHOR]

Three-dimensional velocity models can enable accurate earthquake location, improved seismic hazard assessment, and can enhance our understanding of geodynamic processes. This is particularly true for areas such as the Aegean, where the crust is marked by active volcanoes as well as shear and rift zones, all of which make this region highly heterogeneous. This work describes the application of local earthquake tomography in order to elucidate the crustal structure of the Aegean. We utilized a dataset of 2,135,625 P arrivals and 1,095,515 S arrivals from 178,676 events recorded across 324 stations. Results indicate that the boundary separating the slow V p from the fast anomalies at 20–40 km depth is well correlated with the Aegean Moho obtained from receiver functions. A slow V p (−5%) zone at depths >30 km along the Hellenic arc is likely associated with basal underplating that forms the base of the crust. On the other hand, fast V p and moderate to high V p /V s (1.77–1.92) in the upper-middle crust may indicate evolving metamorphic core complexes. Steeply dipping clusters of earthquakes could highlight pathways of fluid migration from the base to the middle/upper crust, albeit more detailed seismological studies are needed to confirm this interpretation. The 3D velocity model can be also utilized in order to investigate the amount of melt fraction beneath active volcanoes and the influence of fluids on the rupture zone of large earthquakes. Our results show a melt fraction between 4 and 10% beneath active volcanoes, with the largest volume of melt present beneath Santorini caldera. The ruptures zones of 10 large earthquakes (M w ≥ 6.0), show slow V p anomalies and moderate to high V p /V s (> 1.77), suggesting that these events were likely triggered by weakening of their source zones by fluid activity. • Inversion of P and S-wave travel times from 178,676 events recorded by 324 stations. • Slow to fast V p anomaly change at depths >20 km matches receiver function Moho. • Low V p and high V p /V s near large event hypocenters imply fluid-induced weakening. • 4–10% porosity (melt fraction) found under volcanoes, the highest below Santorini. [ABSTRACT FROM AUTHOR]

The Nullarbor Plain is underlain by thick cratonic lithospheric mantle that is almost devoid of contemporary seismicity. Analysis of high‐resolution digital elevation models indicates neotectonic fault‐propagation fold traces on the nearly flat karst landscape that locally extend to lengths of >100 km, suggesting potential for hosting large (>7.3–7.5) moment magnitude earthquakes. Along‐strike maximum displacements are not proportional to neotectonic fold surface trace length but are spatially associated with crust‐scale electrical conductors identified in magnetotelluric surveys. Two major conductors penetrate from the upper crust to the uppermost mantle (at depths < 60 km) along crustal scale shear zones. Conductivity in the uppermost mantle shear zones is higher than conductivity at increased depth, suggesting fluid‐enhanced enrichment with hydrogen and/or carbon. Lithospheric fluid localization associated with ancient slab subduction and/or hydrothermal alteration may have weakened pre‐existing faults and enhanced neotectonic faulting in the Nullarbor Plain. Plain Language Summary: Stable cratons on the Earth are generally considered to be immune from large earthquakes. Historical seismic quiescence and a paucity of evidence for geologically recent activity on large intraplate faults can result in an absence or low level of seismic hazard awareness, though intraplate earthquakes have caused more fatalities than interplate earthquakes. Long recurrence intervals commonly obscure evidence for paleo‐earthquakes because surface erosional processes may erode or bury surface ruptures and other neotectonic deformational features. Finding an ideal place that can provide sufficient observations of intracontinental active faults is challenging but pivotal for unraveling intracontinental fault dynamics and seismic hazard assessment. The nearly flat Nullarbor Plain in South‐Central Australia is covered by 100s‐m‐thick limestone, which is cut by reactivated reverse faults propagating upward from the Precambrian basement. The limestone has been exposed to the surface since the mid‐Miocene. The arid climate in this region has helped preserve these neotectonic features from surface erosion. Fault traces with high displacements can be well correlated with patches with high electrical conductivities, which are sensitive to fluids in the lithosphere. With co‐located seismic reflection profiles, gravity, and magnetic maps, we propose that enhanced neotectonic activity is associated with fluids ascending from deeper parts of the lithosphere. Key Points: The Nullarbor Plain in Australia is a cratonic region with neotectonic fault (fold) traces of 7–150 km lengthFault displacement is not positively related to fault length but is spatially linked to high electrical conductors in the lithosphereLithospheric fluid localization is proposed to have weakened pre‐existing faults and enhanced neotectonic faulting in the Nullarbor Plain [ABSTRACT FROM AUTHOR]

Summary: Buildings may need large damping force under severe or near‐fault earthquakes, while existing friction dampers still need a high preload to provide enough reaction forces. In order to provide large damping forces at a small preload, this study proposes a new type of response‐amplified friction damper (RAFD) based on the amplification mechanism of a ball screw pair that combines the advantages of a friction damper and inerter device. The friction mechanism and the restoring force formula of the RAFD were derived theoretically, then pseudo‐static tests with various parameters were conducted. Finally, a single‐degree‐of‐freedom (SDOF) structure was employed to compare the effectiveness of the RAFD with a conventional friction damper under various earthquake levels. The results show that the RAFD has a significant friction amplification effect and significantly reduces the seismic responses of the SDOF structure. Particularly, the proposed RAFD with preload only 2 kN results in better effectiveness than the conventional friction damper with preload up to 20 kN. According to the pseudo‐static tests, the derived theoretical model can accurately describe the hysteresis behavior of the RAFD. A smaller gap in the RAFD can further improve the effectiveness in response mitigation. [ABSTRACT FROM AUTHOR]

Seismic hazard assessment in slow straining regions is challenging because earthquake catalogues only record events from approximately the last 100 years, whereas earthquake recurrence times on individual faults can exceed 1,000 years. Systematic mapping of active faults allows fault sources to be used within probabilistic seismic hazard assessment, which overcomes the problems of short-term earthquake records. We use Shuttle Radar Topography Mission (SRTM) data to analyse surface deformation in the Luangwa Rift in Zambia and develop the Luangwa Rift Active Fault Database (LRAFD). The LRAFD is an open-source geospatial database containing active fault traces and their attributes and is freely available at: https://doi.org/10.5281/zenodo.6513691. We identified 18 faults that display evidence for Quaternary activity and empirical relationships suggest that these faults could cause earthquakes up to Mw 8.1, which would exceed the magnitude of historically recorded events in southern Africa. On the four most prominent faults, the median height of Late Quaternary fault scarps varies between 12.9 ± 0.4 and 19.2 ± 0.9 m, which suggests they were formed by multiple earthquakes. Deformation is focused on the edges of the Luangwa Rift: the most prominent Late Quaternary fault scarps occur along the 207 km long Chipola and 142 km long Molaza faults, which are the rift border faults and the longest faults in the region. We associate the scarp on the Molaza Fault with possible surface ruptures from two 20th Century earthquakes. Thus, the LRAFD reveals new insights into active faulting in southern Africa and presents a framework for evaluating future seismic hazard. [ABSTRACT FROM AUTHOR]

Pliocene–Quaternary faults are relevant structures with which to constrain the seismotectonic context and contribute to the evaluation of the seismic hazard of a region. Many of these faults, however, do not show clear surface evidence even when releasing earthquakes. For these reasons they can be extremely dangerous as they receive relatively little attention and can be difficult to identify. From among the various surface geology studies and/or palaeoseismological investigations, we focus our attention on the integration of different datasets such as seismic reflection profiles, surface kinematic data and the relocation of seismological data, which make it possible to identify and characterize active faults whose dimension and earthquake potential would otherwise not be large enough to make them identifiable. We take as an example the Montespertoli NE-trending fault in southern Tuscany (central Italy) with which we associate the 2016 M=3.9 Castelfiorentino earthquake. This structure is part of a wider (in the order of 15–20 km) crustal-scale shear zone, which may be responsible for strong historical earthquakes in the area. [ABSTRACT FROM AUTHOR]

Records of near‐fault ground motions from recent surface‐breaking earthquakes are characterized by large (> a few m/s), long‐period (a few seconds) ground velocity pulses, which may pose significant hazard for tall buildings and large infrastructures. Yet, the generation mechanism is not well understood. Here, using spontaneous rupture simulations, we examine the origin of large velocity pulses observed during the 2016 Mw7.0 Kumamoto (Japan) earthquake. We show that near‐fault waveform data as well as seismologically estimated moment and radiated energy can be well reproduced by a relatively simple model with uniform along‐strike pre‐stress and frictional properties. Our results suggest that large, long‐period ground velocities are caused by the dynamic interaction of propagating rupture and the Earth's surface, which is enhanced by reflected waves from the boundaries of low‐velocity layers. Such a generic mechanism suggests that large, long‐period ground motion is a common occurrence in near‐fault regions during surface‐breaking, strike‐slip earthquakes. Plain Language Summary: Recordings of ground motions during recent large earthquakes show unusually large amplitudes and long duration in the vicinity of the fault rupture. How and why such ground motions were generated remains mystery. We utilize both the numerical simulations of earthquake rupture and ground motion data to investigate the origin of unusually large and long‐duration ground motions observed during the 2016 magnitude 7.0 Kumamoto (Japan) earthquake. We find that the observed ground motions can be well explained by a model that accounts for the interaction of propagating earthquake rupture with the Earth's surface. We provide an explanation for why unusually large and long‐duration ground motions are expected in the regions close to the fault ruptured during any surface‐breaking, strike‐slip earthquake. Our study highlights the important role of rupture dynamics in estimating seismic hazard for tall buildings and large infrastructures (e.g., dams and bridges) in major cities around the world. Key Points: Relatively simple, dynamic rupture model reproduces near‐fault waveforms and source characteristics of the 2016 Kumamoto earthquakeLarge, long‐period ground velocities in near‐fault regions can be explained by the interaction of propagating rupture and Earth's surfaceFree surface effect on dynamic rupture propagation is enhanced by reflected waves from the boundaries of low‐velocity layers [ABSTRACT FROM AUTHOR]

Based on field investigations, interpretations of high‐resolution UAV images, and analyses of available InSAR data, we mapped the fault geometry and surface ruptures of the 2021 Mw 7.4 Maduo earthquake that occurred on a low‐activity strike‐slip fault within the Tibetan Plateau. The results indicate that (a) the earthquake activated a fault that is ∼161 km long and has complicated structural geometry; (b) the surface rupture occurs over a distance of 148 km, but is separated into three distinct segments by two large gaps (38 and 20 km, respectively); (c) within the surface‐rupture segments, the horizontal and vertical displacements are typically 0.2–2.6 m (much lower than the InSAR‐based slip maximum of 2–6 m at depth) and ≤0.4 m, respectively. The two large gaps of the Maduo surface rupture represent the two largest surface‐rupture discontinuities of strike‐slip earthquakes ever documented, and coincide with structurally complicated fault portions and near‐surface soft sediments. Plain Language Summary: Evaluating the seismic potential of low‐activity strike‐slip faults is commonly challenging because of (a) the difficulty in mapping of causative fault geometry that has subtle topographic expression, and (b) limited fault slip at the surface (relative to that at depth) produced by each earthquake. Our investigation of the 2021 Maduo earthquake demonstrates that, along the low‐activity strike‐slip fault, laterally significant gaps (up to 40 km wide) may separate extensive co‐seismically ruptured regions on either end of such gaps, which can thereby compromise typical methodologies used to assess paleoseismic ruptures and may lead to underestimates of seismic hazard. This observation increases the challenge of assessing the seismic potential of low‐activity strike‐slip faults. Key Points: The Maduo earthquake activated a 161‐km‐long strike‐slip fault with subtle topographic expression and complicated structural geometryThe surface rupture occurs over a distance of 148 km, but includes two large gaps that are 38 and 20 km, respectivelyWithin the surface‐rupture segments, the horizontal slip is 0.2–2.6 m, much lower than the InSAR‐based slip maximum of 2–6 m [ABSTRACT FROM AUTHOR]

Assessing the built environment's seismic risk relies increasingly on numerical simulations of the response of infrastructure components to seismic motion. Since forecasting earthquake-induced motion is difficult, if not impossible, subjecting the infrastructure to seismic motion from past earthquakes remains the most potent way to assess the infrastructure's risk and resilience. However, such simulations require a rupture-to-rafters modeling approach that entails complex inversion procedures and ultra-scale computations. In this work, we discuss a systematic methodology that attempts to reconstruct the earthquake-induced wavefield only within the near-surface deposits, using ground surface recordings of seismic motion. The methodology improves on alternative approaches by bypassing the need for either seismic source inversion or joint seismic-source-and-material-model inversion, relying instead on a priori knowledge of the soil properties for only the near-surface deposits, thus realizing significant computational savings. The methodology takes advantage of a state-of-the-art, near-surface, seismic wave motion simulation framework rooted in the Domain Reduction Method (DRM), which relies on a reduced computational domain containing the near-surface deposits only, including possible topographic features and even accounting for materially-nonlinear response. The reduced domain is surrounded by an artificial boundary – the DRM boundary –, onto which the seismic input is typically prescribed in forward seismic motion simulations. A narrow wave-absorbing buffer exterior to the DRM boundary completes the computational domain. It is the aim of this work to reconstruct the DRM seismic input from ground-surface records using an inversion approach rooted in partial differential equation (PDE)-constrained optimization, without having to appeal to fault rupture inversion or joint inversions. To this end, we use the DRM, enhanced with a Complex-Frequency-Shifted (CFS) Perfectly-Matched-Layer (PML), to address the forward wave simulation, and an adjoint approach to address the inversion of the DRM seismic input. Our numerical experiments demonstrate the versatility of the methodology in reconstructing the near-surface seismic motion from sparse surface motion records, almost irrespective of the azimuthal coherency of the incoming motion. • The total seismic wavefield is reconstructed in sites affected by seismic events. • Wavefield reconstruction based on sparse ground-surface sensor data. • Seismic force inversion with no a priori knowledge of the seismic source. • Wavefield reconstruction in heterogeneous deposits. • Seismic force inversion for incident motion of arbitrary content and incoherence. [ABSTRACT FROM AUTHOR]

Normal faults are commonly segmented along strike, with segments that localize strain and influence propagation of slip during earthquakes. Although the geometry of segments can be constrained by fault mapping, it is challenging to determine seismically relevant segments along a fault zone. Because slip histories, geometries, and strengths of linkages between normal fault segments fundamentally control the propagation of rupture during earthquakes, and differences in segment slip rates result in differential uplift of adjacent footwalls, we used along-strike changes in footwall morphology to detect fault segments and the relative strength of the mechanical links between them. We applied a new geomorphic analysis protocol to the Wassuk Range fault, Nevada, within the actively deforming Walker Lane. The protocol examines characteristics of footwall morphology, including range-crest continuity, bedrock-channel long profiles, catchment area variability, and footwall relief, to detect changes in strike-parallel footwall characteristics. Results revealed six domains with significant differences in morphology that we used to identify seismically relevant fault segments and segment boundaries. We integrated our results with previous studies to determine relative strength of links between the six segments, informing seismic hazard assessment. When combined with recent geodetic studies, our results have implications for the future evolution of the Walker Lane, suggesting changes in the accommodation of strain across the region. Our analysis demonstrates the power of this method to efficiently detect along-strike changes in footwall morphology related to fault behavior, permitting future researchers to perform reconnaissance assessment of normal fault segmentation worldwide. [ABSTRACT FROM AUTHOR]

Earthquake ground surface ruptures provide insights into faulting mechanics and inform seismic hazard analyses. We analyze surface ruptures for 11 historical (1968-2018) moment magnitude (Mw) 4.7-6.6 reverse earthquakes in Australia using statistical techniques and compare their characteristics with magnetic, gravity, and stress trajectory data sets. Of the total combined (summative) length of all surface ruptures (~148 km), 133 km (90%) to 145 km (98%) align with the geophysical structure in the host basement rocks. Surface rupture length (SRL), maximum displacement (MD), and probability of surface rupture at a specified Mw are high compared with equivalent Mw earthquakes globally. This is attributed to (1) a steep cratonic crustal strength gradient at shallow depths, promoting shallow hypocenters (~1-6 km) and limiting downdip rupture widths (~1-8.5 km), and (2) favorably aligned crustal anisotropies (e.g., bedrock foliations, faults, fault intersections) that enhanced lateral rupture propagation and/or surface displacements. Combined (modeled and observed) MDs are in the middle third of the SRL with 68% probability and either the ≤33rd or ≥66th percentiles of SRL with 16% probability. MD occurs proximate to or directly within zones of enhanced fault geometric complexity (as evidenced from surface ruptures) in 8 of 11 earthquakes (73%). MD is approximated by 3.3 ± 1.6 (1σ) x AD (average displacement). S-transform analyses indicates that high-frequency slip maxima also coincide with fault geometric complexities, consistent with stress amplifications and enhanced slip variability due to geometric and kinematic interactions with neighboring faults. Rupture slip taper angles exhibit large variations (-90% to +380% with respect to the mean value) toward rupture termini and are steepest where ruptures terminate at obliquely oriented magnetic lineaments and/or lithology changes. Incremental slip approximates AD between the 10th and 90th percentiles of the SRL. The average static stress drop of the studied earthquakes is 4.8 ± 2.8 MPa. A surface rupture classification scheme for cratonic stable regions is presented to describe the prevailing characteristics of intraplate earthquakes across diverse crustal structural-geophysical settings. New scaling relationships and suggestions for logic tree weights are provided to enhance probabilistic fault displacement hazard analyses for bedrock-dominated intraplate continental regions. [ABSTRACT FROM AUTHOR]

In order to generate plate tectonics, the near surface layer should not be too strong, but the causes for not-so-strong near surface layer remains unclear. We conduct mantle convection modelling in the spherical geometry to investigate the influence of the strength of the near surface layer. We explore a range of friction coefficients including the static high friction coefficient (∼0.6) as well as the reduced friction coefficients by fast fault motion in earthquakes. When the friction coefficient is low enough (<0.03), the surface layer is yielded by the convective stress, and the style of mantle convection appears the mobile-lid mode (plate tectonics style of convection). This style is relevant for the Earth where fault motion is unstable because of the low surface temperature. In contrast, for a high friction coefficient, the surface layer is too strong, generating the stagnant-lid mode. This case corresponds to Venus where fault motion is stable because of high surface temperature. Our calculations show that, in plate tectonic style of convection, the mantle convection is likely to be more vigorous, inducing the high convective stress that helps the operation of plate tectonics. In contrast, when stagnant-lid mode of convection appears, the convective vigor is likely to be low, inducing the low convective stress. Therefore, in each case, the interplay between the surface strength and convective stress tends to maintain the same mode of convection in a self-consistent way. We also investigate the relationship between mantle temperature and heat flux for two different modes of convection upon a change in friction coefficient. We found that the heat flow associated with mobile lid convection caused by low friction is less sensitive to the mantle temperature compared to a conventional mantle convection model, where the heat flow is highly sensitive to mantle temperature. This provides a possible mechanism to solve the thermal runaway paradox. [ABSTRACT FROM AUTHOR]

Innovative hybrid-segmented pipeline systems are being used more frequently in practice to improve the performance of water distribution pipelines subjected to permanent ground deformation (PGD), such as seismic-induced landslides, soil lateral spreading, and fault rupture. These systems employ joints equipped with anti-pull-out restraints, providing the ability to displace axially before locking up and behaving as a continuous pipeline. To assess the seismic response of hazard-resistant pipeline systems equipped with enlarged joint restraints to longitudinal PGD, this study develops numerical and semi-analytical models considering the nonlinear properties of the system, calibrated from large-scale test data. The deformation capacities of two hybrid-segmented pipelines are investigated: (i) hazard-resilient ductile iron (DI) pipe and (ii) oriented polyvinylchloride (PVCO) pipe with joint restraints capable of axial deformation. The numerical analysis demonstrates that, for the conditions investigated, the maximum elongation capacity of the analyzed DI pipe system is greater than that of the PVCO pipeline. The implemented semi-analytical approach revealed that the pipeline performance improves strongly by increasing the allowable joint displacement. Comparison of the numerical results with analytical solutions reported in recent research publications showed excellent agreement between the two approaches, highlighting the importance of assigning appropriate axial friction parameters for these systems. [ABSTRACT FROM AUTHOR]

To ensure environmental and public safety, critical facilities require rigorous seismic hazard analysis to define seismic input for their design. We consider the case of the Trans Adriatic Pipeline (TAP), which is a pipeline that transports natural gas from the Caspian Sea to southern Italy, crossing active faults and areas characterized by high seismicity levels. For this pipeline, we develop a Probabilistic Seismic Hazard Assessment (PSHA) for the broader area, and, for the selected critical sites, we perform deterministic seismic hazard assessment (DSHA), by calculating shaking scenarios that account for the physics of the source, propagation, and site effects. This paper presents a DSHA for a compressor station located at Fier, along the Albanian coastal region. Considering the location of the most hazardous faults in the study site, revealed by the PSHA disaggregation, we model the ground motion for two different scenarios to simulate the worst-case scenario for this compressor station. We compute broadband waveforms for receivers on soft soils by applying specific transfer functions estimated from the available geotechnical data for the Fier area. The simulations reproduce the variability observed in the ground motion recorded in the near-earthquake source. The vertical ground motion is strong for receivers placed above the rupture areas and should not be ignored in seismic designs; furthermore, our vertical simulations reproduce the displacement and the static offset of the ground motion highlighted in recent studies. This observation confirms the importance of the DSHA analysis in defining the expected pipeline damage functions and permanent soil deformations. [ABSTRACT FROM AUTHOR]

The Iranian Plateau has been subjected to destructive earthquakes throughout its history. Reliable assessment of the seismic hazard in this earthquake-prone region is therefore essential. Our study focuses on estimating the maximum earthquake magnitude as one of the main parameters of seismic hazard analysis. We implemented two quantitative approaches, namely, probabilistic and deterministic. The probabilistic method allows combining the historical (i.e. incomplete) and the instrumental parts of a catalogue with different levels of completeness and considers the uncertainties in earthquake magnitude determination. In this study, we used a unified, declustered, and complete catalogue of earthquakes in Iran, covering the period from the fourth century BC to 2019. We calculated the maximum possible magnitudes for hundreds of grid points by using the seismicity data in a 200-km radial region around each grid point. The maximum possible earthquake was observed to vary between 6.0 and 8.2, and the highest values were found in the Alborz-Azarbayejan seismotectonic province, Kopeh-Dagh, central east Iran, Makran, and the southeast Zagros. The lowest mmax values were found in the Persian Gulf, Arabian Platform, Esfahan-Sirjan region, and the Dasht-e-Kavir Desert in central Iran. As a second part to this study, we calculated the maximum credible earthquakes for 1103 identified major faults by using five empirical magnitude-scaling relationships. Our results were consistent with both the observed earthquakes and the seismic potential of the various seismogenic zones of Iran. The study results can be used in future seismic hazard analyses and have fundamental implications for mitigating seismic risk in Iran. [ABSTRACT FROM AUTHOR]

We study the Tenes Abou El Hassan (TAEH) fault-related fold of the Tell Atlas (the site of the 1922 Mw 6.2 earthquake) using field investigations combined with satellite image processing. The 1922 earthquake is also revisited through previous reports, publications and contemporaneous newspapers in order to locate the area of maximum ground motion and its relation to the active TAEH fault-related fold. The analysis of high-resolution (0.5 m) satellite imagery (panchromatic Pleiades tri-stereo images) allows the accurate study in tectonic geomorphology and the characterization of active and seismogenic deformation. High-resolution DEMs obtained from Pleiades images highlight alluvial and marine terraces with cumulative uplift during the Upper Pleistocene–Holocene period and allowed the identification of geomorphological markers along the active fold with recognition of complex tectonic structures. The fault-related fold is modelled using both elastic (Okada 1992) and kinematic (Trishear) approaches using balanced cross-sections that reveal 1.2 mm/year shortening rate during the Upper Pleistocene–Holocene. Uplift rate calculated using marine and alluvial terrace altitudes is ~0.3 mm/year during the Upper Pleistocene along the Allalah Quaternary basin and the coastal zone reaching ~1 mm/year during the Holocene. The earthquake geology and correlation between surface deformation and seismotectonic modelling provides additional constraints on the 1922 earthquake fault parameters and related seismic hazard assessment in the Tell Atlas of Algeria. [ABSTRACT FROM AUTHOR]

River long profiles are widely used as tectonic event markers. Incision/uplift rate estimations based on the dating of river terrace or exposed scarp sediment give long-term averaged uplift rate values with the limitation of not giving the intermediate phases of highs and lows. On the other hand, GPS based estimates provide only decadal-scale uplift rate estimates. In our study, we adopted the long profile inversion methodology to obtain a temporal profile of uplift rate history (over the Late Pleistocene-Holocene time period) along an active fault (the Kuchchh Mainland Fault) in Kuchchh region, western India, which has experienced several large magnitude earthquakes in recent past. We also used long profiles analysis to quantify the transient response of Kuchchh landscape to uplift activity along the Kuchchh Mainland Fault. Steepness index and chi profiles were estimated to display the spatial variability in landscape disequilibrium. Integral method-based chi profiles were used to obtain the optimum value of basin area exponent of the Stream Power Incision Model (SPIM). Our estimates provide a mean uplift rate value of 1.1–1.4 mm/yr along the Kuchchh Mainland Fault during the Late Pleistocene-Holocene period, which matches with the average uplift rate derived from other independent observations in this region. Further, a chronology of major tectonic phases from the estimated uplift rate time series also corroborates with field-based estimates of major incision events in Kuchchh region. We also tested the robustness and sensitivity of our uplift rate estimates to model parameters. Such data can be complementary to the existing sparsely (both spatially and temporally) distributed uplift rate database, which is imperative to seismic hazard assessment. [ABSTRACT FROM AUTHOR]

Thick sediment layers frequently cover the Japan islands' surface, and their frictional properties significantly affect the shallow slip behavior that occurs during earthquakes. However, laboratory data on the properties of the shallow zone remain limited. We collected tuff breccia samples from deep borehole cores in the Miocene "Green Tuff" formation, a major surface cover, and performed velocity-stepping friction tests on these samples under in situ stresses of 2 to 20 MPa to assess the velocity dependence of their frictional strength. The samples exhibit predominantly frictionally stable, velocity-strengthening behavior over the range of normal stresses tested, which supports the hypothesis that shallow sediment layers are seismically quiescent. This result is consistent with the low seismicity and attenuation of coseismic slip occurring in the shallow zone that is observed during regional earthquakes. Microstructural observations of the postmortem samples using optical and scanning electron microscopes indicate a fabric transition from boundary shear localization to distributed cataclastic flow with increasing normal stress. Our laboratory investigation of the depth-variable distribution of the frictional velocity dependence of a shallow sediment layer would provide further insight into the mechanical role for earthquake rupture dynamics and shallow seismicity. [ABSTRACT FROM AUTHOR]

The geometries (i.e., dip angles) of active faults from the surface to the seismogenic zone are the most important factors used to evaluate earthquake ground motion, which is crucial for seismic hazard assessments in urban areas. In Osaka, a metropolitan city in Japan, there are several active faults (e.g., the Uemachi and Ikoma faults), which are inferred from the topography, the attitude of active faults in surface trenches, the seismic reflection profile at shallow depths (less than 2 km), and the three-dimensional distribution of the Quaternary sedimentary layers. The Uemachi and Ikoma faults are N–S-striking fault systems with total lengths of 42 km and 38 km, respectively, with the former being located ~ 12 km west of the latter; however, the geometries of each of the active faults within the seismogenic zone are not clear. In this study, to examine the geometries of the Uemachi and Ikoma faults from the surface to the seismogenic zone, we analyze the development of the geological structures of sedimentary layers based on numerical simulations of a two-dimensional visco-elasto-plastic body under a horizontal compressive stress field, including preexisting high-strained weak zones (i.e., faults) and surface sedimentation processes, and evaluate the relationship between the observed geological structures of the Quaternary sediments (i.e., the Osaka Group) in the Osaka Plain and the model results. As a result, we propose geometries of the Uemachi and Ikoma faults from the surface to the seismogenic zone. When the friction coefficient of the faults is ~ 0.5, the dip angles of the Uemachi and Ikoma faults near the surface are ~ 30°–40° and the Uemachi fault has a downward convex curve at the bottom of the seismogenic zone, but does not converge to the Ikoma fault. Based on the analysis in this study, the dip angle of the Uemachi fault zone is estimated to be approximately 30°–40°, which is lower than that estimated in the previous studies. If the active fault has a low angle, the width of the fault plane is long, and thus the estimated seismic moment will be large. [ABSTRACT FROM AUTHOR]

Designing a seismic source model based on the most complete description of potentially active faults and on the kinematics of their latest movements is an essential requirement in seismic hazard studies, at regional and local scales. A study to characterize active faults in the Hispaniola island (today's Haiti and Dominican Republic) has been conducted in the framework of the probabilistic seismic hazard assessment for Santo Domingo (capital of the Dominican Republic). In this work, we present a seismotectonic map of Hispaniola and its surroundings, based on a compilation and synthesis of geological, geophysical, geodetic and seismological data. Based on these data, distinct seismic zone sources are proposed and classified as either intercrustal domains, major active faults or subduction zones. Each seismic source is described according to several parameters, including its mechanism and current rate of deformation, the associated seismicity and its estimated maximal magnitude. These results constitute an essential database for a homogeneous evaluation of the seismic hazards of Hispaniola. [ABSTRACT FROM AUTHOR]

Structural fault complexity at depth affects seismic hazard, earthquake physics, and regional tectonic behavior, but constraining such complexity is challenging. We present earthquake source models of the February 21, 2008, Mw 6.0 Wells event that occurred in the Basin and Range in the western USA, suggesting the rupture of both the shallow and deep parts of a listric fault. We use a large data set including 150 local seismic waveforms from the USArray combined with high‐quality Interferometric Synthetic Aperture Radar and teleseismic waveforms. Rather than imposing an a priori fault geometry in the source inversions, as is often done in the literature, we use a data‐driven approach whereby all the faulting parameters and number of faults are determined by the data alone. We find a two‐fault normal faulting solution comprising: (i) a shallow (centroid depth ∼4.6 km) sub‐event with Mw 5.3 and fault dip of ∼77°; and (ii) a deeper (centroid depth ∼8.8 km), larger Mw 6.0 sub‐event on a fault with shallower dip angle (∼41°). Our preferred two‐fault model is consistent with aftershocks and with the tectonics of the region. The local USArray waveforms used in the modeling are key to detect the rupture of both shallow and deep parts of the possible listric fault. The lack of such dense and uniform coverage of earthquakes in other regions on Earth may explain why the full seismic rupture of listric faults may have gone undetected in the past. Thus, earthquake slip on whole listric faults may be more common than previously thought. Plain Language Summary: The role of fault complexity on the earthquake source process remains debated. An example of such complexity includes so‐called listric faults, which are curved faults whose curvature decreases with depth. While these faults are common worldwide, it is not clear whether earthquakes rupture whole listric fault structures or only parts of them. We studied the February 21, 2008, Mw 6.0 Wells, Nevada event that occurred in the Basin and Range in the western USA using a large data set including local and teleseismic waveforms, as well as Interferometric Synthetic Aperture Radar (InSAR) data. We find that the 2008 Wells earthquake ruptured the shallow and deep parts of a possible listric fault. While the teleseismic and InSAR data cannot resolve the shallow part of the rupture, the local seismic data are key to constrain the deep and shallow parts of the rupture. The lack of dense and uniform local data coverage of earthquakes in other regions on Earth may explain why the full seismic rupture of listric faults may have gone undetected in the past. Thus, earthquake slip on whole listric faults may be more common than previously thought. Key Points: The 2008 Wells earthquake ruptured the shallow and deep parts of a listric faultNear‐field USArray data are key to constrain the deep and shallow parts of the ruptureTeleseismic and geodetic data cannot resolve the shallow part of the rupture [ABSTRACT FROM AUTHOR]

Keywords: Biaxial friction apparatus; Low to high slip velocity; Deformation conditions of the seismogenic upper crust EN Biaxial friction apparatus Low to high slip velocity Deformation conditions of the seismogenic upper crust 2039 2052 14 03/30/21 20210401 NES 210401 Introduction Physics of earthquake source can be investigated by monitoring active faults from borehole observatory in reservoirs (Maxwell et al. [28]) or by interpretation of seismic waves at the earth's surface (Shearer [38]). Tests were performed at room pressure and temperature conditions, imposing normal stress between 10 and 70 MPa, and sliding velocities between 10 SP -5 sp and 2*10 SP -2 sp m/s. Figure 6 shows the resulting friction versus normal stress at different velocities. It consists of a real-time IO Controller CompactRIO (National Instruments), which allows data acquisition at rates up to 50 kHz and real-time control of the normal stress, confining pressure, pore fluid pressure, temperature and slip velocity or shear stress. [Extracted from the article]

Studies in archeoseismology were conducted in the Ferghana Valley revealing traces of strong earthquakes that occurred in ancient times. We pointed out in our previous publications that the ancient city of Eilatan perished in the 1st century BC when devastated by a strong earthquake. It was during that time that the capital Farghana (Akhsiket) was damaged. We also detected there a seismic rupture at the surface and other evident deformations in the previous structural elements. We determined the magnitude of the seismic disaster (М = 7.6) based on the greatest displacement on the seismogenic rupture emerging at the surface right in the middle of the ancient city. The associated seismic motion completely destroyed or considerably deformed all structures and seriously damaged and destroyed the city walls. It was probably for that reason that the new kings of the Ferghana Valley built a new residence for themselves on Mugtepe after the 90s BC. The site is referred to in a Chinese source Hanshu as Guishuan. We have succeeded to determine from data to be found in archeological sources that the abovementioned fortifications in the capital were built in the time span 104–90 BC, while the intensity X earthquake itself seems to have occurred approximately in 91–90 BC. The earthquake involved all of the Ferghana Valley, hitting the towns and villages in the northern Ferghana especially heavily. A conspicuous example is furnished by the falling-apart of massive fortress walls in the citadel and the Shahristan of the town of Farghana (Ahsiket). It is possible that the seismogenic rupturing that emerged at the surface in the ancient Ahsiket and Eilatan occurred at the same time. A similar strong earthquake occurred later on, during the 11th to the earlier half of the 12th century. We identified traces of this seismic event at several objects of the Karahanid age in the shakhristan and rabad. These materials must be incorporated for a new assessment of earthquake hazard for the Ferghana Basin. [ABSTRACT FROM AUTHOR]

However, paleoseismic studies elucidate that the WLSG has experienced several historical earthquakes with magnitude 6.5-7.0, therefore, strong earthquakes may also occur in lowFigure 1 T ectonic background of the seismic gap between the W enchuan and Lushan earthquakes. Backgr ound on the seismic gap between the W enchuan and the Lushan earthquakes The 2008 M w 7.9 W enchuan earthquake and the 2013 M w 6.9 Lushan earthquake, which occurred in the Longmenshan fault system (hereafter called LMSFS), caused dramatically casualties and huge economic losses. Moreover, the W enchuan and Lushan earthquakes greatly increase the Coulomb failure stresses in the WLSG, thus increasing the possibility of strong earthquakes (Guo et al., 2020). [Extracted from the article]

The earthquake Frequency Magnitude Distribution (FMD) or b values have been meticulously used in the last two decades as a deterministic earthquake precursor or indicator, in earthquake forecasting or probabilistic seismic hazard assessment studies, in a variety of tectonic and stress regimes. In the present study, temporal fluctuations of b values were analysed by means of 185 well located (Mw ≥ 5) earthquakes, in the region of Andaman and Nicobar Islands (N10° to 14°) for a time period of ∼100 years (1918 to 2018). Variation in b value rates before and after the 2004 great Sumatra-Andaman earthquake (Mw 9.3) was analysed, preceded by a comprehensive geodynamic and seismotectonic- crustal deformation overview along the Andaman trench section. The analysis suggest a precursory drop in b values from 1.05 ± 0.05 (1918 to 2004) to 0.90 ± 0.05 post 2004 earthquake (2004 to 2018) reflecting a greater slip deficit and strain localization, that exceeds considerably the pattern of energy release in this region. Further, the region of Andaman and Nicobar Islands have witnessed a poor slip distribution (on-fault reactivation) from the great earthquakes that nucleated near the Sumatra segment, and have ruptured few large earthquakes, with no accounts of great earthquake (>Mw 8) during the last century. This emphasizes that, strain accumulation has been concentrated over a long period of time, and can contribute a destructive deformation event in near future. [ABSTRACT FROM AUTHOR]

The low frequency of large destructive earthquakes in the Eastern Betics (SE Iberian Peninsula), not recorded in the instrumental seismic catalog, complicate the estimation of the maximum ground motion that could be reached. Knowing the characteristics and behavior of these large seismic ruptures is crucial for the study of seismic hazard. In this work, we have used a physics-based earthquake simulator to generate a 100 kyr catalog of seismic ruptures associated with seismogenic faults bordering the quaternary Guadalentin and Bajo Segura basins. From these ruptures, we have selected maximum earthquake scenarios, and those associated with certain probabilities of exceeding a severe magnitude from the synthetic catalog. The estimation of maximum peak accelerations (PGA) by means of ground motion prediction equations include a possible site amplification that we have calculated from a detailed geotechnical classification of soils. According to the simulations, the modeled faults have the capacity to generate maximum earthquakes with magnitudes ranging M W 6.7–7.4. Densely populated urban areas located along the Guadalentin valley, such as Lorca, could be subject to site-dependent PGA values close to 0.6 g on the Alhama de Murcia fault trace. Similar ground motion would affect the coastline of SE Alicante province when evaluating the maximum simulated event in the Bajo Segura offshore fault. But already from magnitudes around M W ∼ 6, PGA estimations exceed critical values of 0.5 g at the south side of the Bajo Segura basin and the city of Murcia, highly dependent of ground-motion amplification induced by thick deposits of very soft and saturated soils. Our scenarios reflect that other factors such as fault geometry, kinematics and the capability observed in the simulations to generate multi-fault ruptures also affect the spatial distribution of maximum ground motion in this region. We expect that this evaluation could contribute as an improvement guideline for future strong motion prediction studies prior to the settlement of new urban infrastructures in the Eastern Betics. • Physics-based simulations for a long-term catalog of large complex seismic ruptures. • Deterministic analysis of ground motion scenarios at the Eastern Betics. • Geotechnical classification of soils to include site amplification in hazard analysis. • Big earthquakes and soft soils may rise seismic threat in populated zones of SE Spain. [ABSTRACT FROM AUTHOR]

Geodetic observations and seismic inversions suggest that the 2021 Mw7.4 Maduo earthquake's rupture velocity differs in two directions. However, the dynamic mechanisms underlying these differences remain unclear. To address this issue, we constructed a three-dimensional finite element model implementing heterogeneous fault geometry and real topography and simulated the Maduo earthquake's dynamic rupture process, with the tectonic stress field varying with depth. The results show that the uneven distribution of normal and shear stresses on the fault plane, due to the complex geometry of the seismogenic fault, is the primary factor controlling rupture velocity and slips on the fault plane of the Maduo earthquake. The modelled results reproduced basic kinematic characteristics as indicated by the observation and inversion results of the Maduo earthquake. Our study also suggests that if an earthquake occurs in a region without significant changes in velocity structure and stress field distribution, the complex geometry of the seismogenic fault is responsible for the dynamic rupture process. These findings provide important insights into the rupture behaviour of geometrically complex faults and have important implications for seismic hazard assessments of these complicated fault systems. • The dynamics rupture process of the 2021 Maduo earthquake was modelled. • The modelled results reproduced the rupture process indicated by the geodetic observations and seismic inversions. • Stress heterogeneity due to the complex fault geometry is responsible for the asymmetric and uneven rupture process. [ABSTRACT FROM AUTHOR]