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Currently, the study of analytical solutions for the seismic stability of slopes under anchorage conditions is one of the hottest subjects in engineering. In this paper, an analytical solution for the seismic safety of the three-dimensional (3D) two-stage rock slope reinforced with prestressed anchor cables governed by the nonlinear Hoek–Brown criterion was deduced, in which the analyses of seismicity were performed by the latest modified pseudo-dynamic method. This method supplements the consideration of the damping effect of the rock medium on seismic waves, which is more in line with the real seismic situation. A mathematical geometric model was developed for calculating the external forces work and internal energy dissipation acting on 3D rotating rock masses reinforced with prestressed anchor cables, in which the seismic work rate was calculated using a new layer-by-layer superposition summation method. The analytical solution of the safety factor could be collated as an explicit function of several variables, and then, the optimal value was obtained by the Particle Swarm Optimization (PSO) algorithm. To corroborate the accuracy of new analytical solutions, the results were contrasted with those of the pertinent literature. The results of the two comparisons were very close. Ultimately, the sensitivity analyses and coupling effects of seismic pseudo-dynamic factors and prestressing anchorage factors were carried out. It was found that even small seismic intensities had a large effect on the stability of rock slopes with developed joints. Increasing the number of steps and prestressing anchors can effectively improve the stability of rock slopes under seismic effects. The conclusions have significant implications for the anchorage design of the 3D two-stage rock slope as seismic events occur. [ABSTRACT FROM AUTHOR]

Seismic imaging techniques play a crucial role in interpreting subsurface geological structures by analyzing the propagation and reflection of seismic waves. However, traditional methods face challenges in achieving high resolution due to theoretical constraints and computational costs. Leveraging recent advancements in deep learning, this study introduces a neural network framework that integrates Transformer and Convolutional Neural Network (CNN) architectures, enhanced through Adaptive Spatial Feature Fusion (ASFF), to achieve high-resolution seismic imaging. Our approach directly maps seismic data to reflection models, eliminating the need for post-processing low-resolution results. Through extensive numerical experiments, we demonstrate the outstanding ability of this method to accurately infer subsurface structures. Evaluation metrics including Root Mean Square Error (RMSE), Correlation Coefficient (CC), and Structural Similarity Index (SSIM) emphasize the model's capacity to faithfully reconstruct subsurface features. Furthermore, noise injection experiments showcase the reliability of this efficient seismic imaging method, further underscoring the potential of deep learning in seismic imaging. [ABSTRACT FROM AUTHOR]

The seismic wavelet, also known as the "far-field wavelet," plays a crucial role in various stages of seismic data signal processing. Accurately obtaining the far-field wavelet has become a key challenge in seismic signal processing. Existing methods for obtaining the far-field wavelet have certain limitations, while methods based on direct waves to extract the source wavelet are complex and difficult to implement. In this study, an exploration of the characteristics of direct waves in marine seismic data reveals that the far-field wavelet is essentially the zero-offset direct wave. Building upon this understanding, we propose a simplified method to extract the far-field wavelet using direct waves from marine seismic data. The method involves simulating the impulse response of direct waves with different ghost wave delays to calculate the filter factors. This process facilitates the conversion of direct waves with variable offsets, referred to as "offset filtering". Throughout the calculation process, the filter factors remain unaffected by the source signal, focusing solely on the time delay effect between the direct waves and the source ghost waves in seismic traces with different offsets. As a result, the entire calculation process demonstrates a high level of stability. By applying the obtained filter factors to the actual direct wave data in marine seismic records, we can obtain the corresponding far-field wavelet. Testing and processing of real seismic data validate the simplicity, practicality, and ability of this method to yield high-precision seismic wavelets. [ABSTRACT FROM AUTHOR]

While the Earth (rocky planet) can be approximated as an elastic body, it also possesses anelasticity, Q−1, which causes energy dissipation (intrinsic attenuation) during deformation. Rock deformation experiments have demonstrated that Q−1 shows a marked amplitude dependency for strain of >∼10−6, but seismic‐waves‐induced strain is generally much smaller than the threshold value. Therefore, all seismological analyses have assumed amplitude‐independent attenuation. However, theoretical models of dislocation‐induced attenuation have predicted amplitude‐dependent attenuation under high temperatures and pressures equivalent to the crustal and uppermost mantle conditions. This study investigates whether attenuation is actually independent of seismic‐wave amplitudes by a systematic analysis of a large number of spectral amplitudes of co‐located earthquake pairs with different observed amplitudes. We assume the ω2 source and circular crack models to correct for the source parameters of earthquakes. The obtained results suggest that amplitude‐dependent attenuation is required to explain the observations, which contradicts a long‐standing recognition that amplitude‐dependent attenuation is negligible for the propagation of seismic waves. Our model calculation further suggests that Q−1 is proportional to the seismic amplitude, A, whereby Q−1 ∝ A0.1–0.2, which introduces attenuation variations along a given raypath, with significantly enhanced attenuation near the hypocenter. Our result highlights the need to revisit and potentially rethink current models of the physical mechanisms influencing intrinsic attenuation. Plain Language Summary: When seismic waves propagate in the Earth, their strain energy is gradually lost by the energy dissipation due to grain‐boundary sliding or dislocations during internal deformation. This study investigates whether the energy of seismic waves loses during their propagation in the crust and uppermost mantle by the systematic analysis of large number of seismic waveforms. Our result reveals that the energy dissipation depends on amplitude of seismic waves with 0.1–0.2 power of the amplitude. This finding is different from a long‐standing common recognition that attenuation is independent for amplitudes comparable to seismic waves. Our results highlight the merit of revisiting conventional observations, models, and hypotheses in the Earth and planetary sciences, where all the existing studies have assumed amplitude‐independent energy dissipation. Key Points: We analyzed spectral ratios of co‐located earthquakes with different amplitudes to extract amplitude‐dependent attenuationThis study suggests that amplitude‐dependent attenuation occurs in the crust and the uppermost mantle during the seismic‐waves propagationSeismic attenuation is proportional to the amplitude to the power of 0.1–0.2 [ABSTRACT FROM AUTHOR]

The Canary and Madeira Islands are two distinct hotspots in the Central‐East Atlantic that are close to each other. Their volcanism is generally attributed to underlying mantle plumes, but the detailed structure of these plumes is still not well understood. The thermal and compositional structure of the plume introduces complexities in the phase transitions of the mantle, which impact the depth and magnitude of seismic discontinuities. We use 1,268 high‐quality receiver functions from stations located at the two hotspots to detect P‐to‐s converted phases through a common‐conversion point stacking approach and conduct a detailed analysis of mantle seismic discontinuities. The results show that both hotspots are characterized by a thin mantle transition zone (MTZ), with sharp 410 and 660 discontinuities at depths of 428–421 km and 647–664 km, beneath the Canaries and Madeira respectively. The results indicate that the Canary plume crosses the MTZ, whereas the Madeira plume mainly influences the upper portion of the MTZ. Furthermore, we find reliable detections of a sharp X discontinuity beneath the Canaries at 287 km. Its presence suggests the accumulation of silica‐rich recycled eclogite at these depths. We also use the amplitudes of P410s and PXs to derive velocity jumps at corresponding discontinuities. Based on these measurements, we estimate that the basalt proportion is 60%–80%, with accumulation being more significant in the Canaries than in Madeira. The MTZ thickness, the presence of the X discontinuity, and the high basalt proportion provide compelling evidence for a deep‐rooted thermochemical plume beneath the study area. Plain Language Summary: We examine the Canary and Madeira Islands, two separate groups of islands in the Atlantic Ocean, close to each other. While it is generally accepted that volcanic activity in these regions is driven by underlying mantle plumes, the precise characteristics of these plumes remain relatively unknown. Tomography studies have revealed distinct structures of the plumes, with the Canary plume extending vertically throughout the upper mantle, while the Madeira plume is visible up to a depth of 300 km, beyond which the resolution of the images deteriorates. We use receiver functions, derived from the analysis of seismic waveforms, particularly the conversion of compressional waves to shear waves at seismic discontinuities within the Earth. Receiver functions offer a higher resolution compared to tomographic images, primarily due to their ability to directly measure seismic wave conversions at specific depths, reflecting where mantle minerals change their crystal structure. This analysis provides insights into the variations in temperature and mineral chemistry in the mantle, as both factors influence the depths of crystal rearrangements. Our research provides evidence supporting the existence of a deep‐seated thermochemical plume beneath the study area. However, beneath Madeira, the plume may be less vigorous or presently disconnected from its deep source. Key Points: We investigate the upper mantle discontinuities below Canary and Madeira using P receiver functionsDeeper 410 in both, shallower 660 in Canaries, normal in Madeira: suggests Canary plume crosses MTZ, Madeira plume only affects upper MTZDetection of X discontinuity suggests a deep‐rooted thermochemical plume [ABSTRACT FROM AUTHOR]

Several studies suggest that large earthquakes (M > 7.0) can act as external triggers of volcanic unrest, and even eruption. This triggering is attributed to either ground shaking (dynamic stresses) or to permanent ground deformation (associated with static stress changes). However, large earthquakes are rare and testing triggering hypotheses has proven difficult. We use geodetic data to show that the 13 November 2016 Kaikōura earthquake (Mw 7.8) triggered local deformation of up to 11 mm at Taupō volcano, 500 km away, which lasted for approximately twelve days. Using elastic geodetic models, we infer that the observed deformation was caused by either aseismic fault slip or a dike intrusion. We then use strong motion data from the surrounding area to show that the Kaikōura earthquake caused maximum dynamic stress changes in the range of 0.15–0.9 MPa in the vicinity of Taupō volcano and conclude that these dynamic stress changes triggered local faulting or dike activity and the associated deformation at Taupō volcano. Plain Language Summary: It has often been proposed that large earthquakes can trigger volcanic eruptions. However, large earthquakes are rare and testing these triggering hypotheses is therefore difficult. We show that the 13 November 2016 Kaikōura earthquake triggered local ground movement at Taupō volcano, 500 km away, which lasted for approximately two weeks. We show that the observed ground movement was caused by either slow movement on a fault or by the movement of magma at depth. We then use seismology data from the surrounding area to show that the Kaikōura earthquake caused large pressure changes in the vicinity of Taupō volcano. We conclude that the ground shaking from the earthquake caused local faulting or magmatic activity and the associated ground movement at Taupō volcano. Key Points: The Mw7.8 Kaikōura earthquake was followed by local deformation at Taupō volcano, c. 500 km awayThe deformation observed is consistent with either a dike intrusion or aseismic slip on a faultDynamic stress changes in the range of 0.15–0.9 MPa caused by seismic waves from the Kaikōura earthquake triggered this response at Taupō [ABSTRACT FROM AUTHOR]

Subduction of carbonate‐bearing oceanic plates into Earth's interior recycles carbon from the surface to the deep mantle. The subducted carbonates can significantly affect mantle properties and dynamics. Magnesite is recognized as one of the major potential carbon hosts in the deep mantle because of its stability up to deep lower mantle conditions. However, despite many previous studies on the equation of state and elastic properties of magnesite, large discrepancies still exist for its elastic moduli and their pressure and temperature derivatives. Here we report in situ density and elastic wave velocity measurements on a natural magnesite at simultaneous high pressure‐temperature conditions up to ∼8 GPa–1073 K in a multi‐anvil apparatus using ultrasonic and synchrotron X‐ray techniques. Global fitting of the data set to finite strain equations yields KS0 = 114.0 ± 1.2 GPa, KS′ ${K}_{S}^{\prime }$ = 4.9 ± 0.3, ∂KS∂TP ${\left(\frac{\partial {K}_{S}}{\partial T}\right)}_{P}$ = (−0.019 ± 0.002) GPa/K, G0 = 68.6 ± 0.4 GPa, G′ = 1.6 ± 0.1, and ∂G∂TP ${\left(\frac{\partial G}{\partial T}\right)}_{P}$ = (−0.018 ± 0.001) GPa/K. Compared to other major upper mantle and transition zone minerals, magnesite has intermediate VP, the lowest VS, and the lowest density. Thus, magnesite possesses higher VP/VS ratio than other mantle minerals in normal mantle regions, whereas this feature is less pronounced in subduction zone environments. Modeling of the velocity profiles of carbonated lithologies along different geotherms suggests that moderately‐enriched magnesite domains are unlikely to be detected seismically in the Earth's mantle. Plain Language Summary: Carbon can be transported into Earth's interior by subducting slabs in the form of carbonates. Magnesite (MgCO3) is recognized as one of the most important oxidized carbon hosts inside the Earth. Accurate knowledge of the thermoelastic properties of magnesite at Earth's mantle conditions is thus needed in order to evaluate its seismic detectability and effect on mantle seismic structure and dynamics. Despite many previous efforts in determining the properties of magnesite, large discrepancies still exist for its elastic moduli and their pressure and temperature derivatives. In this study, we determined both the density and elastic wave velocity of magnesite at high pressure and temperature conditions up to ∼8 GPa–1073 K using in situ ultrasonic measurements combined with synchrotron X‐ray techniques in a multi‐anvil press. Our high‐quality data tightly constrained the thermoelastic parameters of magnesite, which were then used to model the velocity and density of magnesite and magnesite‐bearing rocks in the Earth's mantle along different geotherms. Our results show that despite the fact that magnesite has the lowest VS compared to other major mantle minerals, moderately‐enriched magnesite domain is difficult to detect in the Earth's mantle based on its seismic velocity. Key Points: In situ density and elastic wave velocity measurements on magnesite at simultaneous high P‐TThe thermoelastic properties of magnesite are tightly constrained by high‐quality P‐ρ‐T‐VP‐VS data setModerately‐enriched magnesite domains are difficult to detect seismically in the Earth's mantle [ABSTRACT FROM AUTHOR]

At Tanis, a unique bi‐directional sediment package occurs precisely at the Cretaceous‐Paleogene (K‐Pg) boundary, recording the first hours of the Paleogene in uncommonly fine temporal detail. The impact ejecta‐bearing sediment package was rapidly emplaced by two massive, ∼10‐m‐high, potentially impact‐triggered surges, that inundated a steep, deeply incised paleo river valley from the direction of the contemporaneous Western Interior Seaway (WIS). Intermingling of fresh‐ and salt‐water fossils at Tanis, coeval brackish water indicators in the nearby region, and historical tsunami observations, suggest that the WIS paleoshoreline was nearby Tanis at K‐Pg time. The interpreted timing for deposition (including ejecta infall) of ∼1–2‐hr immediately post‐impact precludes a direct tsunami from the Chicxulub impact site, which would have required much more than 10 hr to reach Tanis. Seismic waves from the Mw ∼ 11 Chicxulub earthquake, arriving just minutes post‐impact, might have triggered the surge, for example, via seismic excitation of large water waves in the WIS, as proposed by DePalma et al. (2019, https://doi.org/10.1073/pnas.1817407116). Here, we explore this mechanism via a simple mathematical model of seismic excitation and propagation of a water wave into a shallow river and upstream. Matching the observations implies a relatively long source process time of many minutes, such as generated by Chicxulub crater rebound processes, in order to explain sufficient upriver amplitudes and advective transport. Atmospheric waves due to the expanding Chicxulub ejecta curtain might have provided a smaller, secondary contribution during triggering. Thus, the mechanism(s) for the surges at Tanis are now better‐constrained, yet remain incompletely resolved. Plain Language Summary: A remarkable geological record at the "Tanis" site (North Dakota) shows that two ∼10 m high tsunami‐like surges occurred on a point bar along a river upstream from the then existing Western Interior Seaway (WIS). The surge deposits are interpreted to have occurred within 1–2 hr of the Chicxulub impact associated with the end‐Cretaceous mass extinction including the dinosaurs, and are challenging to explain via traditional tsunami mechanisms because they occurred too soon after the impact to have been tsunami waves traveling from the impact site. Alternative explanations include excitation of large water waves in the WIS due to seismic shaking from the magnitude ∼11 impact‐generated earthquake or atmospheric effects from the expanding impact ejecta curtain. Here, we explore one potential triggering mechanism via a simple mathematical model of direct seismic excitation and propagation of a water wave into a shallow river and upstream. This model shows the difficulty of generating the observed surge deposits unless the timescale for impact‐generated seismic waves is much longer than is commonly presumed. Thus the actual triggering mechanism(s) of the Tanis depositional surges remains incompletely resolved, while the sediment package bears a rich source of information about the global effects of the Chicxulub impact. Key Points: An ∼10 m surge event coincident with the Chicxulub impact transported mixed freshwater/marine organisms up the Tanis river valleyNew modeling confirms limitations on the inland transport of marine fossils and helps to constrain the impact‐related triggering mechanismOther potential triggering mechanisms and strategic avenues of future study are discussed [ABSTRACT FROM AUTHOR]

Ambient Noise Imaging (ANI) of subsurface structures relies on seismic interferometry of diffuse seismic wavefields. However, the lack of effective methods to quantify and identify highly diffuse waves hampers applications of ANI, particularly in evaluating seismic attenuation and monitoring structural changes with high temporal resolution. Conventional ANI approaches require data normalization, which effectively suppresses the non‐diffuse component with large amplitude but also results in significant loss of amplitude and phase information in the continuous seismic records. In this study, we propose a frequency domain method to quantitatively evaluate the degree of diffuseness of seismic wavefields by analyzing their statistical characteristics of modal amplitudes for stationarity and randomness. Tests on synthetic waveform and field nodal records show that the proposed method can effectively distinguish between diffuse and non‐diffuse waveforms for either single‐ or three‐component data. As an application, we identify a 60‐s‐long diffuse coda of a local M 2.2 earthquake recorded by a dense nodal array on the San Jacinto Fault Zone, and successfully extract high‐quality dispersion curve and Q‐value without performing data normalization. These results are consistent with those obtained by conventional methods that assess the correlation between coherency and the Green's function, and by modeling ballistic waves generated by road traffic. Our proposed method can advance the imaging of subsurface velocity and attenuation structures as well as monitoring temporal changes for scientific studies and engineering applications. Plain Language Summary: Earthquakes, explosions, and traffic events can generate seismic waves that travel through the Earth. As these direct waves encounter heterogeneous earth interior, they scatter and change direction, leading to more diffusive propagation. Fully diffuse waves can be used to image the subsurface structures. In this study, we develop a reliable and efficient method to measure how diffuse a seismic wavefield is at different frequencies. Tests on synthetic and field data show that the developed method can reliably differentiate between diffuse and non‐diffuse waves. This method can improve our ability to use spread out wavefields for imaging and monitoring the Earth's interior. Key Points: We present an efficient methodology to quantify seismic wavefield diffuseness based on stationarity and randomness in the frequency domainThe method avoids waveform normalization and extracts reliable empirical Green's functions from interferometry using diffuse waveformsWe validate the method by extracting dispersion curves and Q‐values from the 60‐s‐long diffuse coda of a local M 2.2 earthquake [ABSTRACT FROM AUTHOR]

This study utilized ambient seismic noise tomography to investigate correlations of hydrogeological systems with heterogeneous porosity with the internal velocity structure of karst aquifers using the Floridan Aquifer System (FAS) as an example. We conducted a seismic signal analysis with 30 days of vertical component seismic data acquired within the Santa Fe River Sink‐Rise system (Sink‐Rise System), using power spectral density estimates and frequency‐wavenumber analysis to identify any noise source biases. Empirical Green's functions were derived through phase cross‐correlations and phase‐weighted stacking. The functions allowed extraction of group velocity dispersion measurements, which were inverted to generate 2D tomographic images at various periods. Tomographic images show multiple layers with varying group velocities that aligned with known hydrogeological features of the FAS, including its base, low‐porosity and low‐permeability dolostone semiconfining units characterized by elevated velocities, and zones of elevated porosity from karstification with reduced seismic velocities. Our results show how ambient seismic noise can be used to evaluate aquifer physical properties, identify unknown features, and identify the location and continuity of aquifer units. Plain Language Summary: We used ambient seismic noise to evaluate the speed of seismic waves in the subsurface to understand hydrologic properties of the rocks within a karst aquifer. We analyzed seismic data collected over 30 days in the Santa Fe River Sink‐Rise system in north‐central Florida. The seismic signal sources originate from ocean waves, anthropogenic activity, and weather. Using cross‐correlation techniques, we measured the time lag of the seismic signals as they traveled between seismic station pairs, from which we obtained surface wave (Rayleigh) velocity. Finally, inversions of the velocity measurements provide 2D images of the subsurface at various depths that show alignment of several seismic velocity layers with aquifer units. Dolostone semiconfining units are indicative of elevated seismic velocities, which correspond with low porosity, while lower seismic velocities correspond with porous karstic zones. This study shows the utility of ambient seismic noise to evaluate heterogeneous hydrologic systems and improves our understanding of the depth, thickness, and extent of the aquifer units. Key Points: Seismic tomography reveals the internal velocity structure of the Floridan Aquifer System and its correlation with hydrogeological unitsSeismic velocities provide details on aquifer relationships, semiconfining units, unknown features, and the degree of karstificationThis study demonstrates the broader applicability of seismic tomography in other aquifer systems [ABSTRACT FROM AUTHOR]

Accurate source parameters of global submarine earthquakes are essential for understanding earthquake mechanics and tectonic dynamics. Previous studies have demonstrated that teleseismic P coda waveform complexities due to near‐source 3‐D structures are highly sensitive to source parameters of marine earthquakes. Leveraging these sensitivities, we can improve the accuracy of source parameter inversion compared to traditional 1‐D methods. However, modeling these intricate 3‐D effects poses significant computational challenges. To address this issue, we propose a novel reciprocity‐based hybrid method for computing 3‐D teleseismic Green's functions. Based on this method, we develop a grid‐search inversion workflow for determining reliable source parameters of moderate‐sized submarine earthquakes. The method is tested and proven on five Mw5+ earthquakes at the Blanco oceanic transform fault (OTF) with ground truth locations resolved by a local ocean bottom seismometer array, using ambient noise correlation and surface‐wave relocation techniques. Our results show that fitting P coda waveforms through 3‐D Green's functions can effectively improve the source location accuracy, especially for the centroid depth. Our improved centroid depths indicate that all the five Mw5+ earthquakes on the Blanco transform fault ruptured mainly above the depth of 600°C isotherm predicted by the half‐space cooling model. This finding aligns with the hypothesis that the rupture zone of large earthquakes at OTFs is confined by the 600°C isotherm. However, it is noted that the Blanco transform fault serves as a case study. Our 3‐D source inversion method offers a promising tool for systematically investigating global oceanic earthquakes using teleseismic waves. Plain Language Summary: Understanding where earthquakes happen and the geometric characteristics of the faults are crucial for studying earthquakes and the Earth's tectonics. Sufficient data collected by seismometers near the fault can help us figure out these details. However, usually only distant seismometers located on land are available for most underwater earthquakes in the vast oceans. Simulating seismic waves propagating from these remote earthquakes all the way to seismometers on land is computationally expensive. To save costs, traditional simulations typically use a depth‐dependent Earth model. In other words, the ocean is excluded or is included with a flat seafloor. These simplifications cause significant error because the real non‐flat seafloor results in much more complicated seismic waves. Here, we develop a computationally inexpensive method to accurately model how seismic waves propagate in an Earth model with non‐flat seafloor. We demonstrate that this more accurate modeling can dramatically improve the earthquake source parameter estimation, especially the depth. We test this method using five moderate‐sized earthquakes on the Blanco transform fault and confirm its high accuracy. The reliable depths indicate that all these earthquakes happened at depths with temperatures lower than 600°C. This method can be applied globally to study submarine earthquakes. Key Points: A hybrid method is proposed to efficiently model complex teleseismic body waves due to 3‐D source‐side effects of submarine earthquakesThe source parameters estimation of moderate‐sized submarine earthquakes is improved by using the 3‐D teleseismic Green's functionsThe improved centroid depths of five Mw5+ earthquakes support a seismogenic zone above the 600°C isotherm at the Blanco transform fault [ABSTRACT FROM AUTHOR]

It is reported that earthquakes are accompanied by electromagnetic (EM) anomalies. These anomalies are thought to be caused by earthquakes but their generation mechanism is still unclear. The piezoelectric effect has been proposed as a possible mechanism, particularly in quartz‐rich rocks. However, the EM responses to earthquakes due to such an effect have not been well understood. In this article, we study the EM signals generated by an earthquake source due to the piezoelectric effect. We develop a semi‐analytical method to simulate the EM responses to earthquake sources in a 3‐D layered model and conduct numerical simulations to investigate the characteristics of the EM fields. The results show that the piezoelectric effect in quartz‐rich rocks could be the responsible mechanism for the EM signals recorded during the earthquake. Two kinds of EM signals can be generated by the earthquake, namely, the early EM wave arriving before the seismic waves and the coseismic EM field accompanying the seismic waves. For an Mw 6.1 earthquake, the coseismic electric field is ∼0.1 μV/m and the magnetic field can only reach ∼10−5 nT. We also study the sensitivity of the coseismic EM fields to the rock conductivity. The results indicate that the coseismic EM fields are mainly affected by the conductivity of the shallow layer where the receiver is located, and if the top layer is thin, they are also affected by the conductivity of the deeper layer due to the contribution of the evanescent EM wave created at the interface. Plain Language Summary: When a quartz‐rich rock is under stress, the positive and negative charge centers of quartz crystals are shifted, resulting in a polarization, which manifests macroscopically as the EM radiation. Such a phenomenon is known as the piezoelectric effect. It is a plausible mechanism for the generation of the earthquake‐associated electromagnetic (EM) anomaly. In this paper, we propose a simple method to simulate the EM disturbances generated by an earthquake source arising from the piezoelectric effect. We also conduct numerical simulations to study the properties of the EM fields. The results show that earthquakes can produce two kinds of EM signals. One signal propagates with the speed of the EM wave in the rocks and it arrives earlier than the seismic waves. The other is the coseismic EM field that appears simultaneously with the seismic waves. Such a coseismic signal is restricted to inside of the area disturbed by the seismic wave. Based on the sensitivity analysis, we find that the coseismic EM signal is sensitive not only to the conductivity of shallow rocks, but also to that of the deep rocks. The results also indicate that the electric signals produced by the piezoelectric effect during an earthquake are observable. Key Points: A method is presented to simulate the seismo‐electromagnetic fields due to the piezoelectric effect in quartz‐rich strataAn earthquake source can generate an early electromagnetic (EM) wave and coseismic EM fields due to the piezoelectric effectNumerical results show that the piezoelectric effect is an effective mechanism to produce observable electric signals [ABSTRACT FROM AUTHOR]

We demonstrate the effectiveness of seismic dense array surface wave focal spot imaging using USArray data from the western‐central United States. We study dispersion in the 60–310 s period range and assess the image quality of fundamental mode Rayleigh wave phase velocity maps. We apply isotropic spatial autocorrelation models to the time domain zero lag noise correlation wavefield data at distances of about one wavelength. Local estimates of the phase velocity, its uncertainty, and the regression quality imply overall better ZZ relative to ZR or RZ results. The extension of the depth resolution compared to passive surface wave tomography is demonstrated by the inversion of three clustered dispersion curves from different tectonic units. We observe anisotropic surface wave energy flux and the influence of body wave energy, but sensitivity tests at 60 s targeting the data range, correlation component, and processing choices show that the ZZ focal spots yield consistent high‐quality images compared to regional tomography results in the 60–150 s period range. In contrast, at 200–300 s the comparatively small scales of the imaged structures and the imperfect agreement with low‐resolution global tomography results highlight the persistent challenge to reconcile imaging results based on different data sources, theories, and techniques. Our study shows that surface wave focal spot imaging is an accurate, robust, local imaging approach. Better control over clean autocorrelation fields can further improve applications of this seismic imaging tool for increased resolution of the elastic structure below dense seismic arrays. Plain Language Summary: Seismic tomography is an established imaging method that estimates properties of the medium using information of the seismic waves that propagate between source and receiver. This concept is routinely applied to earthquake waves and also to waves that are reconstructed using seismic noise correlations, and has led to impressive high‐resolution images in areas with high seismic sensor density. Here we apply an alternative imaging approach that has been developed in ultrasound medical imaging to surface wave data from the dense seismic USArray covering the western‐central part of the contiguous United States. In contrast to tomography the focal spot method does not analyze propagating waves but properties of the spatial autocorrelation field. The seismic wave speed and potentially other medium properties are estimated at the location of each seismic sensor using data obtained at other dense array sensors that are closely spaced in terms of the wavelength. The focal spot imaging technique is elegant and simple to implement because it does not involve the solution of an inverse problem. In this work we demonstrate its effectiveness by reproducing images from available USArray tomography results. Key Points: The local Rayleigh wave speed can be estimated from the focal spot, the time domain spatial noise autocorrelation field at short distancesWe use USArray focal spots to image the elastic velocity structure in the 60−310 s period range and compare the results to tomographyClean seismic dense array focal spots can enhance vertical and lateral resolution and feature detection for improved imaging [ABSTRACT FROM AUTHOR]

Based on a new seismic surface wave data set, we present a model of Alaskan crustal seismic anisotropy that provides new insight into Alaska's geographically diverse deformation history. We use both Rayleigh and Love wave isotropic phase speed and Rayleigh wave azimuthal anisotropy to estimate crustal anisotropy. Unlike traditional seismic tomography, which focuses on apparent seismic anisotropy in which the symmetry axis of anisotropy is assumed to be known, we resolve the spatial variation of inherent anisotropy by inferring the depth‐dependent tilt of the hexagonally symmetric elastic tensor. The amplitude of inherent anisotropy is typically stronger in the lower than the upper crust. We principally interpret the dip angle (plunge of the symmetry axis) or the tilt of the anisotropy foliation plane, which reflects the influence of vertically and/or horizontally oriented structures or deformation. The depth variation of crustal anisotropy appears in four principal motifs that partition Alaska into six distinct geographical regions, which display characteristic dip angle patterns in the upper and lower crust. By considering geological context, we discuss how each region reflects active or historical crustal deformation. Plain Language Summary: Geological observations have yielded valuable insight into the deformation history of Alaska, but the understanding of deep crustal processes remains limited. Based on seismic evidence, we present a model of seismic anisotropy that provides information about Alaska's deep crustal deformation. In contrast with most previous anisotropy studies, we focus on the tilt angle of the anisotropy foliation plane, which is caused by arbitrarily oriented structures or deformation. The resulting model partitions Alaska into six geographical regions, with four characteristic vertical tilt motifs in the upper and lower crust. We provide information about deformation in the upper and lower crust in each of these six distinct regions. By focusing on the depth variation of the tilt of anisotropy and its link to deep crustal deformation, this study complements surface geological observations and offers a new perspective on Alaskan tectonics. Key Points: A new crustal anisotropy model of Alaska is built based on a new surface wave data set and a tilted hexagonally symmetric medium assumptionThe crustal anisotropy model partitions Alaska into six distinct regions with four characteristic vertical motifs of anisotropyThe depth variation of the tilt of anisotropy and its link to crust deformation provide new insights about Alaskan tectonics [ABSTRACT FROM AUTHOR]

Subsurface temperature measurements play a crucial role, for instance, in optimizing geothermal power plants and monitoring heat-storage systems. Previous studies have demonstrated that time-lapse variations in temperature can be correlated with variations in seismic wave speeds, offering the potential for temperature monitoring via seismic surveys. However, an apparent discrepancy has emerged between field and laboratory experiments. Field studies predominantly report positive correlations between temperature and seismic wave speeds, while laboratory experiments often show anticorrelations. This inconsistency underscores the need for a more comprehensive, physics-based understanding of temperature-induced wave speed changes. In this study, we strive to bridge the gap between field and laboratory findings by examining several mechanisms governing temperature-induced seismic wave speed changes, namely the intrinsic temperature dependency of elastic parameters and thermally induced elasticity. We present a physics-based modelling approach to identify the primary mechanisms responsible for temperature-induced seismic wave speed changes. By considering several end-member models, we find that intrinsic temperature dependency of elastic parameters (negative correlation) compete with thermal pressure effects (positive correlation). The precise initial and boundary conditions and physical parameters of the system under consideration will determine the weight of both effects. Temperature-related dilatation does not seem to play an important role. We apply our approach to loosely consolidated sediments in the shallow subsurface of the Groningen region, where subsurface temperature fluctuations are driven by seasonal atmospheric temperature fluctuations roughly between −5 and |$30\, ^\circ$| C. For these models, we predict seasonal temperature-induced changes in body-wave speeds of up to 8 per cent in the first few metres of the subsurface, high-frequency (above 2 Hz) surface wave phase velocity variations in the range of 1–2 per cent, and relative changes in site amplification on the order of 4 per cent. These findings contribute to a more comprehensive understanding of the intricate relationship between temperature and near-surface seismic properties, offering insights for applications as subsurface temperature monitoring systems. [ABSTRACT FROM AUTHOR]

The Lijiang–Xiaojinhe fault (LXF) and its vicinity are located in the transition zone among the Tibetan Plateau (TP), the South China block and the Indochina block. Researchers believe that this area has acted as a key tectonic zone during the evolution of the TP. Owing to the continuous growth and SE-ward expansion of the TP, the LXF and its vicinity have experienced intense deformation. Although different models, such as the rigid block extrusion and mid-lower crustal flow models, have been proposed to explain this intense deformation, a consensus has not yet been achieved. To better understand the deformation of the LXF and its vicinity, a high-resolution image of the subsurface structure must be constructed. In this study, we construct images of P -wave velocity and azimuthal anisotropy structures by using an eikonal equation-based traveltime tomography method. We collect high-quality seismic data from 276 broad-band seismic stations and manually pick a total of 48   037 first arrivals for the tomography study. Our tomographic results reveal a strong low-velocity body below the LXF and its vicinity. In addition, a strong azimuthal anisotropy structure with an N–S-oriented fast velocity direction is distributed along the low-velocity body. These features indicate the occurrence of mid-lower crustal flow, that penetrates across the LXF and extends to the Dianzhong block (DZB). In addition, we find obvious low-velocity perturbations in the mid-lower crust and uppermost mantle beneath the DZB. The low velocities may be attributed to the upwelling of hot materials from the upper mantle. We consider the limited distribution of mid-lower crustal flow on the margin of the SE TP, and mid-lower crustal flow may not play a significant role in the expansion of the TP. [ABSTRACT FROM AUTHOR]

Pore pressure oscillations induced by stress variations, including propagating seismic waves from remote earthquakes, have been widely observed in various groundwater systems. The monitored pressure change in wells shows significant water-level oscillations to volumetric strain as well as to S and Love waves. Recent observations demonstrated azimuthal dependence of the pore pressure oscillations with respect to stress indicators and fault zone orientation. Within the fault zone, damage-induced anisotropy is the result of the alignment and orientation of cracks and other internal flaws within the rock. In this work, we provide a complete quantitative description of the pore pressure changes induced by passing seismic waves associated with different orientations and values of principal stress and damage tensor components. The model quantifies the azimuthal dependence of the pore pressure response by a non-dimensional ratio defined as the amplitude of the pressure oscillations induced by a shear strain normalized to the volumetric strain. Three angles and two values are needed to calculate the azimuthal dependence of the pore pressure response: the angle between the directions of the maximum horizontal stress and the seismic event; fault zone orientation; microcrack orientation within the fault zone; and damage and stress values. The model predicts that maximum pore pressure response occurs when microcracks and maximum horizontal stress are in the same orientation, high damage and high stress anisotropy. By adjusting these quantities, we recalculate results of recent seismological studies in the Arbuckle disposal well, Osage County, Oklahoma. The presented model successfully predicts the observed azimuthal dependence in wave-induced fluid pressure response and relates the anisotropic response to tectonic indicators such as the orientations of the maximum horizontal stress, fault zone, and microfractures. [ABSTRACT FROM AUTHOR]

Train traffic is a powerful source of seismic waves, with many applications for passive seismic imaging. Seismic signals were recorded a few metres away from the railway track. These records display harmonious waveforms below 15 Hz for trains driving at speeds of around 100 km hr−1. The sensors record an apparent wavelet emitted by the interaction of the axle on a few of the closest sleepers. From this, we build a simple modelling tool using shifted wavelets to simulate a train signal. The relationship involves the varying train speed, the distances between each axle, and the wavelet emitted by each axle. We propose a nonlinear deconvolution method to invert this relationship. We use a local minimization algorithm with gradients derived by the adjoint state method, and use a frequency continuation technique. A linearized picking-based inversion initializes the nonlinear inversion. On real data, we apply this automatic workflow to 300 train passages, with an excellent match between the best simulation and the data. We identify the trains decelerating as they enter a train station. We also identify the train type based on inverted wheel spacing with centimetric accuracy. The inverted wavelets are consistent with the assumption that trains emit seismic waves by bending the rail above sleepers, although the theory does not explain why the inverted wavelet is not zero phase. This automated kinematic inversion algorithm may allow for contactless railway monitoring, and be used for source characterization for subsurface monitoring below railway tracks. [ABSTRACT FROM AUTHOR]

A recent study the detection of coseismic ionospheric disturbances or ionoquakes less than 400 s from the earthquake's onset. The study also associates these rapid ionoquakes with the seismo-atmosphere–ionosphere (SAI) coupling mechanism energized by acoustic-gravity waves (AGWs) and the subsequent formation of coseismic thermospheric disturbances (CSTDs). The present study outlines a new analytical simulation code for AGWs that resolves the governing equations in the time–altitude and wavenumber domain and confirms the rapid arrival of AGWs in the thermosphere (earlier than the estimated arrival time from the ray-tracing simulation). The rapid arrivals of AGWs are associated with long wavelengths that connect to thermospheric altitudes and propagate with thermospheric sound speeds, avoiding averaging effects from the lower atmosphere. The fast simulation traces the rapid arrival of AGWs in the thermosphere and produces rapid CSTDs within 250–300 s from the earthquake's onset. The simulation time is much shorter than the formation time of near-field CSTDs, a scenario favorable for the forecasting of CSTDs before observations of ionoquakes. In essence, the fast simulation offers an alternative tool for tracking the evolution of CSTDs. [ABSTRACT FROM AUTHOR]

The conversion from seismic to ocean-acoustic waves occurs in different places on the bottom of the ocean, often hundreds to thousands of kilometers away from the epicenter. Here, we investigate this conversion process by studying 15 large-magnitude earthquakes that occurred between 2014 and 2022 along the Kermadec Arc in the southwestern Pacific Ocean. To pinpoint the location where seismic-to-acoustic conversion takes places, we analyze hydroacoustic signals recorded by a hydrophone triplet station of the International Monitoring System in the Juan Fernández archipelago. Results from direction-of-arrival and travel-time calculations indicate that the location of the conversion zone largely matches segments of the Louisville Seamount Chain, its lateral extent ranging from approximately 300 to 1800 km, and its location depending on the geometry between earthquake epicenter and the seamounts. [ABSTRACT FROM AUTHOR]

Understanding the dynamics of slope instabilities is critical to mitigate the associated hazards, but their direct observation is often difficult due to their remote locations and their spontaneous nature. Seismology allows us to get unique information on these events, including on their dynamics. However, the link between the properties of these events (mass and kinematics) and the seismic signals generated is still poorly understood. We conducted a controlled rockfall experiment in the Riou Bourdoux torrent (southern French Alps) to try to better decipher those links. We deployed a dense seismic network and inferred the dynamics of the block from the reconstruction of the 3D trajectory from terrestrial and airborne high-resolution stereophotogrammetry. We propose a new approach based on machine learning to predict the mass and the velocity of each block. Our results show that we can predict those quantities with average errors of approximately 10 % for the velocity and 25 % for the mass. These accuracies are as good as or better than those obtained by other approaches, but our approach has the advantage in that it does not require the source to be localised, nor does it require a high-resolution velocity model or a strong assumption on the seismic wave attenuation model. Finally, the machine learning approach allows us to explore more widely the correlations between the features of the seismic signal generated by the rockfalls and their physical properties, and it might eventually lead to better constraints on the physical models in the future. [ABSTRACT FROM AUTHOR]

This paper presents a novel numerical method for the Newton seismic full-waveform inversion (FWI). The method is based on the full-space approach, where the state, adjoint state, and control variables are optimized simultaneously. Each Newton step is formulated as a PDE-constrained optimization problem, which is cast in the form of the Karush–Kuhn–Tucker (KKT) system of linear algebraic equitations. The KKT system is solved inexactly with a preconditioned Krylov solver. We introduced two preconditioners: the one based on the block-triangular factorization and its variant with an inexact block solver. The method was benchmarked against the standard truncated Newton FWI scheme on a part of the Marmousi velocity model. The algorithm demonstrated a considerable runtime reduction compared to the standard FWI. Moreover, the presented approach has a great potential for further acceleration. The central result of this paper is that it establishes the feasibility of Newton-type optimization of the KKT system in application to the seismic FWI. [ABSTRACT FROM AUTHOR]

We present a detailed one-dimensional (1-D) velocity model of the Lake Van Basin and its surrounding region, alongside precise hypocenter locations, utilizing seismic data from the aftershocks of the 23 October 2011 Lake Van earthquake (Mw = 7.1). The 1-D minimum velocity model is computed by the VELEST program by analyzing body wave traveltimes and station corrections. Encompassing a geographical area of 180 x 90 km² centered around Lake Van, the study incorporated seismic data from 10 newly deployed stations, complementing the existing network of the Kandilli Earthquake Research Institute. A comprehensive manual analysis was conducted on a dataset comprising 7643 events occurring between 23 October 2011 and 21 January 2015. Among these, 1193 well-located events recorded by 16 stations were selected, encompassing 48,387 P-wave and 26,913 S-wave arrival times. The iterative simultaneous inversion technique was applied to refine velocity and hypocenter parameters while mitigating the influence of near-surface velocity heterogeneity and station elevation through station corrections. The resulting 1-D velocity model delineates eight distinct layers up to a depth of 39 km, including a 3-km-thick sedimentary layer, while determining the VP/VS ratio for each layer. Rigorous testing procedures were implemented to ensure the stability and accuracy of the velocity structure and aftershock locations. The relocation of the aftershock sequence using the new 1-D velocity model revealed significant shifts in the distribution pattern, notably concentrating relocated events towards the vicinity of the main shock area. This study underscores the efficacy of the VELEST software in deriving a robust 1-D velocity model and refining hypocenter locations for the Lake Van region. The insights gained enhance our understanding of the region's seismotectonic and have implications for seismic hazard assessment and risk mitigation strategies. [ABSTRACT FROM AUTHOR]

The disturbances in the lower ionosphere during the strong earthquake in Türkiye and Syria and its strongest aftershock on February 6, 2023, are analyzed using data from ground-based magnetometers. The observation points are located at distances 700 to 1600 km from the epicenter of the seismic event. As a characteristic of the ionospheric response to these events, variations in the magnetic field have been analyzed at the İznik, Grocka, Panagjurishte, and Surlari magnetic observatories. Earthquake epicenter is known to be a source of both seismic Rayleigh waves and atmospheric acoustic-gravity waves. Using the difference in velocities, at which these waves propagate from the epicenter, and their spectral composition, we found the ionospheric responses to the events that are interpreted quite well in terms of acoustic waves (produced by seismic Rayleigh wave) and atmospheric internal gravity waves generated in the earthquake epicenter. [ABSTRACT FROM AUTHOR]

We report new PKS, SKS, and SKKS splitting measurements for 88 seismic stations in Namibia, Botswana, South Africa, and Mozambique. When combined with measurements from previous studies, the ensemble of measurements shows a fairly uniform NNE to NE (∼41° on average) fast‐polarization direction (ϕ) and delay time (δt) (∼0.7 s on average) across the entire southern African subcontinent. It is difficult to attribute the NNE‐NE ϕ direction to just one source of anisotropy either within the lithospheric or sublithospheric mantle. We instead propose the observed anisotropy pattern could result from a combination of several sources that together give rise to a pervasive NNE‐NE ϕ direction; (a) fossil anisotropy in the lithospheric mantle resulting from the Neoproterozoic collision of the Congo and Kalahari cratons to form the Damara Belt, (b) movement of the African plate over the asthenosphere, and (c) flow in the upper mantle induced by the African Superplume. In addition, a contribution from anisotropy in the lowermost mantle in the vicinity of the African large low shear velocity province cannot be ruled out. Plain Language Summary: Seismic anisotropy, or the directional dependence in seismic wave speed, reveals the ancient to present orientation of deformation of Earth's interior. In this study, shear waves refracted through the outer core and recorded at 88 seismic stations located in Namibia, Botswana, South Africa, and Mozambique were measured to constrain the anisotropic structure of the upper mantle beneath southern Africa. Our results, combined with previous results, show a consistent NNE‐NE fast polarization direction. This direction cannot be easily explained by a single source of anisotropy caused either by past collisions of different geological blocks in southern Africa or the present movement of the African plate. Instead, we propose the pattern may result from a combination of three sources, (a) ancient deformation preserved within the deep continental lithosphere developed when the Congo and Kalahari cratons collided, (b) movement of the African plate over the asthenosphere, and (c) the flow of upwelling rock in the mantle beneath Africa. Key Points: Shear wave splitting measurement across southern Africa shows a fairly uniform NNE to NE fast‐polarization direction (ϕ)The observed ϕ direction cannot be easily attributed to just one source of anisotropy within the lithospheric or sublithospheric mantleThe ϕ pattern may reflect several geodynamic processes [ABSTRACT FROM AUTHOR]

This article explores the advancements and challenges in seabed prospecting technology, emphasizing the importance of seabed geophysical data in understanding the planet and driving marine energy resource exploration and deep earth science research. It calls for further technical refinement in ocean bottom geophysical prospecting techniques and the integration of seabed exploration technology with big data and artificial intelligence. The article also introduces a special issue on seabed prospecting technology, which includes research papers covering a range of prospecting methods and geophysical applications. The document provides summaries of various research studies related to seismic data analysis and exploration, offering key findings and methodologies used in each study. [Extracted from the article]

Most seismic data used for conventional exploration lack far‐offset signals and effective low‐frequency components. This makes it difficult for conventional full waveform inversion methods to recover the low‐wavenumber components of mid‐ and deep‐layer models. To resolve the bottleneck of ray‐theoretical reflection traveltime tomography, wave equations, such as reflection inversion methods, are receiving increasing attention. We reconstructed a wide‐spectrum velocity model based on the multiscale wave‐equation reflection inversion method for model decomposition. First, using the dynamic image warping method to obtain reflection traveltime residuals, the wave‐equation reflection traveltime inversion was used to recover the low‐wavenumber components of the background model, which also solved the cycle‐skipping problem. Second, the medium‐wavenumber component of the model is then supplemented by the reflection waveform inversion, while the reflectivity model is obtained relying on the least‐squares reverse time migration method. Based on this method, the background and perturbation models are updated alternately and iteratively. At the same time, the stratum structural tensor information was extracted using the perturbed model image to construct a preconditioned operator for the stratum structural constraint, suppress unreasonably high‐wavenumber components in the generalized gradient and improve the geological consistency of the inversion results. Testing of the model using the Sigsbee2b model and seismic field data from the East China Sea showed that, compared with the conventional reflection traveltime tomography method based on prestack depth migration, the wave‐equation reflection inversion strategy with well‐matched information from traveltimes to waveforms significantly improved the accuracy of the middle and deep velocity modelling and enhanced the imaging quality of the whole body. [ABSTRACT FROM AUTHOR]

The data collected by ocean‐bottom seismometers are unique compared to that of land seismic stations and require preprocessing before use. In this study, we focus on preprocessing seismic data obtained from a passive‐source experiment in the Mariana subduction zone conducted by the Institute of Deep‐Sea Science and Engineering, Chinese Academy of Sciences from 2018 to 2019. We outline the steps involved in preprocessing the data, including time correction using the ocean background noise cross‐correlation function, tilt correction using a transfer function and orientation correction based on seismic wave polarization. Our results show that the maximum clock drifting was ∼4 s on two stations (K06 and K20), whereas the rest of the station waveforms have clock drifting of less than 2 s. Among stations, only the K06 station is tilted, and the tilt angle is 19.82°. We use the P‐wave and Rayleigh wave polarization methods to determine the orientation. Our results indicate that the error in the result obtained using the P‐wave polarization method is less than that of the Rayleigh wave polarization method. Additionally, we address the advantages and disadvantages of these preprocessing techniques. Our goal is to offer a comprehensive overview of the preprocessing process, to assist beginners in the field and to serve as a foundation for future research in passive‐source ocean‐bottom seismometers. [ABSTRACT FROM AUTHOR]

Seismic waves propagating in anisotropic earth media suffer from waveform distortion, which leads to degraded resolution in seismic data imaging if this adverse effect is not corrected. Additionally, the wavefields simulated by the traditional coupled pseudo‐acoustic wave equations contain undesired shear wave artefacts and are unstable when Thomsen's anisotropy parameter ε is less than δ. To address these issues, many pure qP‐wave equations are proposed to describe wave propagation in anisotropic media. However, these equations are either low precision or high accuracy but computationally expensive. Considering the trade‐off between the computation efficiency and simulation accuracy, we derive a pure qP‐wave equation from the exact dispersion formula in tilted transverse isotropic media. The newly derived equation has only two higher order partial derivatives, which can better balance the accuracy and efficiency than the previous pure qP‐wave equations. The least‐squares reverse time migration method can balance amplitudes, suppress migration artefacts and improve imaging resolution. Then, based on the newly derived pure qP‐wave equation, we derive the Born modelling operator and adjoint migration operator and develop an anisotropic least‐squares reverse time migration method. To achieve the accelerated convergence, we introduce a generalized minimum residual algorithm to implement the anisotropic least‐squares reverse time migration method. Numerical simulation results show that the proposed pure qP‐wave equation outperforms the previous equations in balancing the trade‐off between accuracy and efficiency. In addition, synthetic examples demonstrate the effectiveness and robustness of our proposed anisotropic least‐squares reverse time migration method in correcting the deviations due to anisotropic effects. [ABSTRACT FROM AUTHOR]

The interaction mechanisms of the underground tunnel passing through the surface structure for a short distance are complex, and there are hidden dangers, with the interaction between the two tunnels having a nonnegligible impact on the seismic performance of the structural system. To explore the interaction law of seismic response between the double tunnel and the surface structure, this study conducted a shake-table test on a surface frame structure–soil–double-tunnel interaction system with a basement, using an actual tunnel project in Zhengzhou, China, as the background. A three-dimensional (3D) numerical model of the system was established using the finite-element analysis software ABAQUS (2021) with the equivalent linear method, and the numerical model's reliability was verified by comparing with the test results. The verified numerical simulation was used to study the interaction between the structures in the system under six different prototype model cases. The research findings revealed that the tunnel's presence reduced the dynamic response of the structural system while amplifying the far-field dynamic response, and the interaction between the two tunnels increased the degree of this reduction and amplification. The frame structure reduced the soil dynamic response while amplifying the acceleration response and shear force of the tunnel. Additionally, the location of weak layers of the frame structure was influenced by the type of seismic wave inputted, while the diameter and crossing location of the tunnel had nonnegligible influences on the dynamic response of the structural system. The research results can serve as a reference to preliminarily determine the interaction laws of the seismic responses of a double-tunnel and adjacent surface frame structures. [ABSTRACT FROM AUTHOR]

This study evaluated the stability of circular tunnels constructed in anisotropic granular soil in the presence of surcharges on the ground surface and seismic loads. The stability problem was solved using the lower bound limit analysis method in conjunction with the finite-element technique. In addition, the modified pseudodynamic technique was employed, which permits seismic accelerations to vary with depth and time, including the impact of amplitude and phase differences between shear and primary waves. The forces exerted by the soil on the tunnel lining vary over the perimeter. Therefore, the ultimate support pressure should at least be equal to the maximum normal stress from the earth surrounding the tunnel. It was discovered that parameters such as the tunnel cover depth, tunnel diameter, magnitude of surcharge, soil friction angle and its degree of anisotropy, seismic acceleration coefficients, period, and frequency of seismic waves determine the support pressure's magnitude and location. The influence of surcharge diminished beyond a certain cover depth and diameter ratio for given soil and seismic wave parameter magnitudes. This study showed that the maximum normal stress was 8.5 times greater than the uniform stress distribution. Furthermore, the support pressure was found to be a maximum of about 45.5% higher for a tunnel cover depth-to-diameter ratio of 3 than for 1%, 34% higher for anisotropy than for isotropic case, 25% higher in the presence of ground surcharge than its absence, and 60% higher for the horizontal acceleration coefficient of 0.3 compared to the static case. [ABSTRACT FROM AUTHOR]

Seismic isolation aims to prevent the direct transmission of seismic wave energy to the main resistant structure. Typically, this is achieved by using a flexible support system that isolates the base of the structural system from the ground, absorbing the relative deformation at the soil–structure interface. Meanwhile, the main structure tends to move as a rigid body on this flexible support. This article proposes an alternative approach for the dynamic characterization of shredded rubber, which is used in geotechnical seismic isolation (GSI). Traditional testing methods are expensive and require specialized equipment, making them less practical for routine determination. The article details the most important parameters needed to evaluate the applicability and effectiveness of the material in the context of GSI. The parameter of interest, i.e. the transverse elasticity module GR, was calibrated numerically from an experimental model of a column of shredded rubber subjected to free vibrations tests. The results were consistent with those obtained from resonant column and hollow cylinder tests. In this way, it is shown that the presented approach is capable of providing valid estimations of the transverse modulus of elasticity of shredded rubber. [ABSTRACT FROM AUTHOR]

Underground rocks are often subjected to seismic waves and blasting excavation, which cause significant changes in physical and mechanical properties. Due to the bedding plane, the mechanical properties of layered rocks with different dip angles become particularly complex under dynamic disturbance. To investigate the damage mechanism of layered specimens under coupled dynamic and static loading, dynamic disturbance tests were conducted on rock-like material with bedding planes. The results show that the cycle times (C) negatively correlate with the peak load. The linearity of the fit is high, with R2 values above 97%. As C enlarges, the loss ratio Rl significantly increases, and the peak load decreases linearly. The strength of the layered samples varies in a "U" shape with the dip angle (θ) for the same dynamic disturbance. The damage patterns were divided into matrix damage (Mode I) and damage along the bedding plane (Mode II), as well as mixed damage forms (Mode III). When θ = 0°, the damage pattern is mainly Mode I. When θ = 22.5°, 45° and 67.5°, the damage form is Mode III. While Mode II dominates the damage pattern of θ = 90°. The characteristics of the acoustic emission source manifest that the specimen tended to expand the damage from the end to the middle as the axial load increased. The damaged surfaces, identified by high energy level damage, closely matched the macroscopic cracks. [ABSTRACT FROM AUTHOR]

In the territory of Dushanbe city, the capital of Tajikistan, detailed geological and geophysical data were collected during geophysical surveys in 2019–2020. The data comprise 5 microtremor array measurements, 9 seismic refraction tomography profiles, seismological data from 5 temporary seismic stations for standard spectral ratio calculations, 60 borehole datasets, and 175 ambient noise measurements. The complete dataset for Dushanbe was used to build a consistent 3D geologic model of the city with a size of 12 × 12 km2. The results of the seismological and geophysical surveys were compared and calibrated with borehole data to define the boundaries of each layer in the study area. The Leapfrog Works software was utilized to create a 3D geomodel. From the 3D geomodel, we extracted six 12 km long 2D geological cross-sections. These 2D geological cross-sections were used for 2D dynamic numerical modeling with the Universal Distinct Element Code software to calculate the local seismic response. Finally, the dynamic numerical modeling results were compared with the amplification functions obtained from the seismological and ambient noise data analysis. The 2D dynamic numerical modeling results allowed a better assessment of the site effects in the study area to support seismic microzonation and the determination of local peak ground acceleration changes in combination with regional seismic hazard maps. In addition, our results confirm the strong seismic amplification effects noted in some previous studies, which are attributed to the influence of local topographic and subsurface characteristics on seismic ground motions. [ABSTRACT FROM AUTHOR]

This study describes the methodology employed to construct a seismic fragility function based on a pre-existing numerical model tailored for underground stations. Employing a dynamic numerical model, a comprehensive analysis encompassing 110 distinct cases was conducted, each varying in soil depth and classification. Seismic waves, conforming to the standard design spectrum, were utilized within these numerical analyses. The formulation of the fragility function within the constructed model follows a structured approach, segmented by damage indices and severity levels. This systematic breakdown serves to outline the fundamental framework for establishing the fragility function, providing insights into its development process. Subsequently, the derived fragility function underwent a rigorous comparative analysis against established seismic fragility functions from prior studies. This comparative assessment serves as a critical evaluation tool, allowing for an appraisal of the suitability and robustness of the newly developed fragility function in relation to existing benchmarks. [ABSTRACT FROM AUTHOR]

Soil and pile interaction could significantly contribute to the response of the system and should be considered in the design prospect. To address some of the uncertainties, a series of 1 g shaking table tests followed by numerical simulations were conducted to address the seismic response of free-head single piles embedded in dry sand subjected to seismic waves of which horizontal acceleration and bending moments are the prime indexes. Subsequently, the validated numerical model was employed to perform parametric studies, focusing on normalized induced kinematic forces based on the soil profile type. The numerical results showed that not only does the soil profile type considerably affect the amplitudes of the maximum normalized seismic forces but also the distributions of these response parameters are highly dependent on soil type. The results also demonstrated that neglecting slippage and/or separation along the soil–pile interface leads to underestimation of the maximum normalized kinematic bending moment and shear force by up to 17.5% and 70%, respectively. Soil type also affects the induced forces by about 60% indicating that the design consequence of which could be dire. Therefore, it is concluded that the effects of slippage and/or separation can be considerable and hence, should be taken into consideration to prevent probable damages in seismic areas. [ABSTRACT FROM AUTHOR]

Seismic methods will be useful for future lunar near‐surface characterization, and high‐fidelity elastic models will be required to aid interpretation of seismic observations. To develop an elastic lunar near‐surface model, we performed ultrasonic velocity measurements of lunar regolith simulant at low confining pressure and developed a rock physics model calibrated to these measurements. Grain contact models based on Hertz‐Mindlin theory produce accurate results at high confining pressure (i.e., several hundred meters or more burial depth) but historically fail to predict observed velocities in unconsolidated media at low pressure. Therefore, we heuristically modified existing models to fit our measured data over a range of porosities and confining pressures. To compare with Apollo 14 and 16 active seismic experiments, we used our new heuristic rock physics model to produce lunar subsurface velocity profiles. We performed ray tracing through our velocity profiles to calculate seismic traveltime, which results in good agreement with first arrivals interpreted from the Apollo experiments. Our model suggests a slightly higher velocity‐pressure dependence than inferred from in situ measurements, which may be due to porosity reduction in the lunar regolith from impact‐induced and natural vibrations. Plain Language Summary: Seismic velocity is the speed at which mechanical waves travel through planetary materials and is controlled by the physical properties of those materials such as density and compressibility. We have created a model that relates seismic velocity to depth and porosity under lunar conditions and have calibrated that model with laboratory measurements of lunar soil simulant at low pressure (i.e., near‐surface) conditions. Using this model, we can predict seismic velocity in the lunar subsurface and compare the modeled velocity with observations from Apollo active seismic experiments. Slight differences between our model and Apollo observations may be due to lower porosity in the lunar soil caused by vibrations from asteroid impact events and seismic quakes. Key Points: We collected ultrasonic velocity measurements of lunar regolith simulant at low confining pressure to calibrate a rock physics modelOur rock physics model predicts shallow lunar seismic velocity in agreement with observations from the Apollo active seismic experimentsOur model may be used in future studies to predict lunar near‐surface seismic velocity under variable resource scenarios [ABSTRACT FROM AUTHOR]

In this study, the atmospheric changes for the 9.0-magnitude Tohoku earthquake, which occurred on March 11, 2011, are analyzed. The March 11, 2011 earthquake was preceded by a large foreshock on March 09, 2011 with magnitude M 7.3 and depth 32 km at 02:45:20 UT near the east coast of Honshu, Japan. The earthquake doesn't limit its effects on the Earth's lithosphere, hydrosphere and biosphere; it also extends its effects to the atmosphere because of the gas emissions, which produce large-scale seismic waves from the ground and release gases into the atmosphere. In this study, the anomalies of the atmospheric parameters are studied by using one of the atmospheric models from the Naval Research Laboratory Mass Spectrometer Incoherent Scatter Extension 2000 (NRLMSISE-00) model data to analyze the atmospheric anomalies of the Tohoku Earthquake on March 11, 2011. The atmospheric parameters of atomic oxygen (O), hydrogen (H), atomic nitrogen (N), helium (He), argon (Ar), molecular oxygen (O2), molecular nitrogen (N2), total mass density (ρ), neutral temperature (Tn), exospheric temperature (Tex) and anomalous oxygen (AO) are used for analysis during the earthquake occurrence. The epicenter of the Tohoku earthquake, with a geographical location of latitude 38.30° N and longitude 142.37° E, is used for the NRLMSISE-00 model as input parameters to analyze the output of atmospheric parameters. To compare the atmospheric changes caused by the earthquake, 5 days before and after the earthquake are considered. To detect where the atmospheric parameters increased or decreased from the earthquake day, the percentage deviation of the NRLMSISE-00 model is applied. The results indicate that there were atmospheric parameter anomalies that occurred a few days before, following and during the earthquake on March 11, 2011. Except for hydrogen (H), all atmospheric parameters average daily percentage deviation values were positive during the 5 days before and after with respect to the main earthquake shock on March 11, 2011. The NRLMSISE-00 model can capture the atmospheric parameter anomalies of the Tohoku earthquake well. [ABSTRACT FROM AUTHOR]

Vertical isolation by dividing the building into two soft and stiff sub-systems benefits from the period shifts and the damping mechanism across the height. However, the displacement demand imposed on the soft sub-system is less applicable in congested urban areas. As a result, in this study, a hybrid system of vertical isolation system benefiting from a tuned soft subsystem divided into upper and lower portions is investigated. A parametric linear 3-Degree of Freedom (DoF) model of the system incorporating mass and frequency ratio of the sub-systems was introduced and analyzed by response spectrum in MATLAB. A closed-form solution for the system frequency and mode shapes was also established. Response spectrum analysis indicates increasing the Tuned Mass Damper (TMD)'s fundamental period to 2.5 times the soft sub-system's, reduces its displacement to more than 40 percent. The Multi Degree of Freedom (MDoF) model of the system is parametrically generated in MATLAB. Time history analysis of the building subjected to 40 records with 2 and 10 percent probabilities of exceedance in 50 years compared with conventional vertical isolation reveals the lower soft sub-system displacement can be reduced up to 45 percent by shifting drift to upper stories. The innovative tuned vertical isolation by demonstrating superior control performance as comprises lower floors' drift may be an applicable solution for adjacent high- and low-rise buildings. [ABSTRACT FROM AUTHOR]

Jeroen Tromp is a geoscientist who was born in the Netherlands and currently holds positions at Princeton University. He has conducted extensive research in seismology, focusing on theoretical aspects of seismology and numerical simulations of seismic wave propagation. Tromp has authored books and over 200 scientific articles, and his research has been supported by various grants and awards. He emphasizes the importance of creativity, integrity, and tenacity in his field, and highlights the need for a strong background in physics and applied mathematics. Tromp's work has also found applications in medical imaging and nondestructive testing. [Extracted from the article]