Seismic Structure Research Articles

Effect of soft sediments modeling on the seismic response of a 3D mid-rise RC building: high-resolution physics-based ground-motion simulations and empirical factors

Ground-motion simulations have progressively become a key resource in earthquake engineering. Nevertheless, the challenge of accurately simulating ground motions in regions with low shear-wave velocities, such as basins and shallow sediments, persists and is often constrained by the associated computational demands. Motivated by the potential unavailability of suites of simulations resolving low velocities for a specific region or site of interest, this work assesses the implications of using different approaches for modeling low shear-wave velocities on structural response. Two methods are investigated: one relies on simulation models capable of resolving low shear-wave velocities, while the other combines simulations that resolve high shear-wave velocities with empirical site amplification factors. An M7 Hayward Fault strike-slip earthquake in the San Francisco Bay Area and a three-dimensional ten-story reinforced concrete building are used as case study. Findings from this work demonstrate significant differences in the prediction of ground-motion intensities and building responses (from moderate to extensive damage) when different modeling methods are employed. Such differences manifest at sites with low shear-wave velocities as well as at stiff sites in their vicinity. This is caused by the concurrent effect of the specificity of the seismic velocity structure for the considered region and wave propagation, which is adequately captured only by the simulation model incorporating the (target) low shear-wave velocity. Evidence from this study indicates that empirical factors should be used and processed (i.e., transfer functions tapering) with consideration for the specific geological characteristics of the domain of interest, especially in regions lacking representation in the databases of historical records, such as the San Francisco Bay Area. From a structural engineering perspective, these insights contribute to a better understanding of the complexities involved in soft sediment modeling and its implications in structural engineering applications.

Physics-informed deep learning quantifies propagated uncertainty in seismic structure and hypocenter determination

Subsurface seismic velocity structure is essential for earthquake source studies, including hypocenter determination. Conventional hypocenter determination methods ignore the inherent uncertainty in seismic velocity structure models, and the impact of this oversight has not been thoroughly investigated. Here, we address this issue by employing a physics-informed deep learning (PIDL) approach that quantifies uncertainty in two-dimensional seismic velocity structure modeling and its propagation to hypocenter determination by introducing neural network ensembles trained on active seismic survey data, earthquake observation data, and the physical equation of wavefront movement. An analysis of an earthquake in southwest Japan using our method revealed that accounting for such uncertainty propagation significantly reduced the bias and uncertainty underestimation in the hypocenter determination, enabling quantitative evaluation of the focal depth relative to the plate boundary. Our results highlight the potential of PIDL for various geophysical inverse problems, such as investigating earthquake source parameters, which inherently suffer from uncertainty propagation.

Geophysical imaging of the subsurface seismic structure of the Chestnut Hill Reservoir earth embankment dam (Massachusetts)

Geophysical imaging of the subsurface seismic structure of the Chestnut Hill Reservoir earth embankment dam (Massachusetts)

Teleseismic evidence for structural heterogeneity in East Japan forearc from seafloor S-net data

We measure and analyze 4381 P-wave and 4307 S-wave arrival times of 48 teleseismic events recorded at 150 stations of a permanent seafloor seismic network (S-net) installed in the outer-rise and forearc region off East Japan. The obtained relative travel-time residuals amounting to ~3 s at the S-net stations are generally negative on the incoming Pacific and Philippine Sea plates and positive on the continental Okhotsk plate, which reflect high and low seismic velocities, respectively. This pattern is generally consistent with previous results on the seismic velocity structure of the crust and upper mantle beneath the East Japan forearc and the outer-rise area. Large early arrivals (~2.0 s) appear in the southern part of the S-net for the teleseismic events in the southwestern direction, which are mainly due to southwestward steepening of the subducting Pacific slab beneath Kanto. In the study region, the Pacific slab is the most significant anomaly with a thickness of ~90 km and a seismic velocity of 5–6 % higher than that of the surrounding mantle. Early arrivals (~1.5 s) also appear at the S-net stations off South Hokkaido, which are caused by northwestward steepening of the Pacific slab beneath the Tohoku-Hokkaido junction area. These results shed new light on the structural heterogeneity and subduction dynamics of the East Japan arc.

Shake-table test study of seismic isolation structure employing a novel metallic spring bearing

Shake-table test study of seismic isolation structure employing a novel metallic spring bearing

Seismic velocity changes from repetitive seismicity at Mauna Loa prior to and during its 2022 eruption

AbstracMauna Loa’s short-lived eruption from late November to early December 2022 marked the culmination of nearly a decade of elevated seismic activity and geodetic inflation. The volcano has been monitored by a network of permanent, short period and broadband seismometers. I used the continuous waveform data from that network starting in 2012 to generate a catalog of seismicity that enhances the US Geological Survey Hawaiian Volcano Observatory’s public seismic catalog with four times the number of earthquakes, which were then grouped by waveform similarity. Analysis of subtle delays in the timing of arrivals of scattered waves between pairs of earthquakes in this catalog yields a history of small changes in the shallow seismic velocity structure of the volcano. Seismic velocities have been shown at other volcanoes to change during unrest and eruption. My results show a decrease in seismic velocity centered on the summit beginning in September 2022, corresponding to the onset of a vigorous precursory swarm of seismic activity and shallow inflation. During the eruption itself, I observe large changes due likely to dike opening along the northeast rift zone and deflation of the summit reservoir. However, seismic velocity changes associated with non-volcanic sources such as ground shaking from large earthquakes and meteorological influences at seasonal and diurnal time scales are also observed, and these dominate the velocity changes prior to the eruption. Proper accounting of these effects will be a requirement for use in real-time monitoring, and this work serves as a starting point in that endeavor for Mauna Loa.

Felt earthquake on March 4, 2024, Mw=5.0, in the Kyungey-Ala-Too ridge

The paper presents the results of the analysis of instrumental and macroseismic data of the strong Kungey earthquake on March 4, 2024, on the border of Kyrgyzstan and Kazakhstan in the Kemin-Chilik fault area. The hypocenter of the earthquake is confined to the focal zone of the catastrophic Kemin earthquake of 1911 with Mw=8.2. The earthquake of March 4, 2024 occurred under the action of submeridional near-horizontal compression, which is typical for the sources of the Northern Tien Shan. The type of motion in the source along the steeply dipping plane NP1 of southwestern strike is a reverse type of motion with a left-sided strike-slip component, along the plane of an eastern strike is a thrust with a right-sided strike-slip component. Before the Kungey earthquake, a ring-shaped seismicity structures formed by earthquakes with depths of up to 33 km, which is a prediction’s factor for strong crustal earthquakes. The earthquake was felt in Almaty (Kazakhstan) and its suburbs with an intensity of 5 points on the MSK-64 scale and had the most significant impact on the megapolis after the Baysorun earthquake of 1990. Data on the macroseismic impact of the Kungey earthquake in Kazakhstan and Kyrgyzstan were collected. An analysis of the records of strong motion instruments based on data from Central Asian stations was carried out.

Increased metamorphic conditions in the lower crust during oceanic transform fault evolution

Abstract. Oceanic transform faults connect the segments of active spreading ridges that slide past each other. In a classical view, transform faults are considered conservative, where no material is added or destroyed. Recent studies, however, suggest that the crust in the transform fault region is deformed during different episodes and is therefore non-conservative. We combine high-resolution 3D broadband seismic data with shipborne potential field data to study ancient oceanic fracture zones in Albian–Aptian aged oceanic crust in the eastern Gulf of Guinea offshore São Tomé and Príncipe. The crust in this region is characterized by a thin, high-reflective upper crust, underlain by a thick, almost seismically transparent lower crust. At the paleo-transform faults, the lower crust, however, comprises reflectors, which dip towards the transform fault and were previously interpreted as extrusive lava flows at an extensionally thinned inside corner. The lower crust therefore defines the target area for inversion and forward modeling of the potential field data. The chosen seismic horizons are used as geometrical boundaries of the crustal model. First, we perform a lateral parameter inversion for the lower crust, which provides vertical columns of density and magnetic susceptibility. Second, we sort the estimated values using a clustering approach and identify five groups with common parameter relationships. Third, we use the clustered lower-crustal domains to define a consistent 3D model of the study area that aligns with the seismic structure and geological concepts, which is preferred over the simple inversion of the first step. The final model generally shows anomalous low susceptibility and medium to high densities close to the buried fracture zones, which reflects increasing pressure and temperature as the transform faults evolved. This is accompanied by a change in metamorphic facies from prehnite-pumpellyite to greenschist. Our model indicates evolving extension and a second magmatic phase during juxtaposition against the trailing ridge segment. These results are in line with recent studies and strengthen the impressions of a widespread non-conservative character of transform faults.

The use of global gravity for mapping the relationship between seismicity and geologic structure in the middle part of Aceh Province, Indonesia

The use of global gravity for mapping the relationship between seismicity and geologic structure in the middle part of Aceh Province, Indonesia

Study on the Shock-Absorption Performance of Isolation Systems in High-Rise Vertically Irregular Double-Story Structures

(1) Research background: The aim of this study was to explore the seismic response of vertically irregular high-rise buildings using a double-layer isolation system. (2) Methods: A 24-story vertically irregular high-rise frame-shear wall structure was designed, and the finite element model of the double-layer isolation structure was established, as well as the models of the seismic structure, the foundation isolation structure, and the story-separated seismic structure. A dynamic time–history analysis of these models under rare ground motion was carried out. (3) Results: The double-layer isolation system has the best isolation effect, followed by the foundation isolation structure, and finally the interlayer structure. The double-layer isolation system can increase the natural vibration period of the structure by 1.25 times, reduce the displacement angle of the layer by about 74.3%, reduce the acceleration of the top layer by about 82.3%, reduce the base shear force by about 59.68%, reduce the overturning moment of the bottom layer by about 68.89%, and reduce the torsion angle of the top layer by about 89.68%. (4) Conclusions: The double-layer isolation system can effectively reduce the overall seismic response of the structure and effectively control the torsional response of the structure, which makes it feasible for application.

Seismic structure of the Wudalianchi volcanic field in Northeast China: insights into magma reservoir and crustal magmatic plumbing systems

Seismic structure of the Wudalianchi volcanic field in Northeast China: insights into magma reservoir and crustal magmatic plumbing systems

Impact of the Offshore Seismograph Network and 3‐D Seismic Velocity Structure Model on Centroid Moment Tensor Analysis for Offshore Earthquakes: Application to the Japan Trench Subduction Zone

AbstractRecently, a widespread and densely continuous‐recording ocean‐bottom seismograph network has been deployed in the Japan Trench subduction zone. Utilizing the offshore network data improves azimuthal station coverage for offshore earthquakes in the Japan Trench subduction zone. It has a potential to obtain centroid moment tensor (CMT) solutions more accurately than conventional analyses using onshore networks and a simple one‐dimensional seismic velocity structure model. In this study, we conducted CMT inversion for subduction zone earthquakes that occurred between 1 April 2017, and 31 March 2024, with a moment magnitude range of 5.2–7.0. We used seismograms obtained from both the offshore and onshore networks. We calculated Green's functions using a three‐dimensional seismic velocity structure model. Our CMT solutions with thrust‐type mechanisms mostly indicated depths and dip angles consistent with the plate interface. For earthquakes in the outer‐rise region, our CMT solutions were characterized as normal‐fault mechanisms. The joint use of the offshore and onshore networks reduced the estimation errors of the CMT solutions compared with the only use of the onshore network, although the optimal solutions were consistent. The dip angles for the thrust earthquakes determined by our analysis were more consistent with the dip angle of the plate boundary than those determined by conventional CMT analyses. Additionally, we found that the conventional CMT analysis could introduce a systematic bias in depth and magnitude determinations. This finding highlights the importance of an offshore seismograph network and a reliable seismic velocity structure model for CMT inversions.

Development of a 3D Geologic Model Used in the Seismic Hazard and Liquefaction Hazard Analysis of Madison County, Tennessee

ABSTRACT Madison County of western Tennessee is approximately 100 km southeast of the New Madrid seismic zone and, thus, is subject to potentially dangerous seismic shaking and liquefaction events. Holocene floodplain alluvium and associated Pliocene/Pleistocene terraces of the Forked Deer and Hatchie Rivers cover a large part of Madison County. Underlying these unconsolidated sediments are approximately ∼650 m of poorly consolidated Paleogene and Cretaceous terrestrial and marine sediments, which are underlain by Paleozoic limestone bedrock. Uniform regional geology used in the 2014 United States Geological Survey seismic hazard maps assumes a homogenous seismic velocity structure above bedrock. Three-dimensional geologic mapping of the ∼700 m of Quaternary, Neogene, Paleogene, and Cretaceous sediments conducted in this study provides a more detailed velocity structure, resulting in a more accurate and detailed map of the expected ground motions in Madison County during future earthquakes. In addition, the surface geologic map reveals regions that are susceptible to liquefaction. This paper discusses the methods used to construct the surface geology map, subsurface structure contour maps, isopach maps, and 3D geologic model used in the seismic hazard and liquefaction hazard analyses of Madison County, Tennessee, and summaries of the results of these analyses are presented.

Seismic Wave Detectability on Venus Using Ground Deformation Sensors, Infrasound Sensors on Balloons and Airglow Imagers

AbstractThe relatively unconstrained internal structure of Venus is a missing piece in our understanding of the formation and evolution of the Solar System. Detection of seismic waves generated by venusquakes is crucial to determine the seismic structure of Venus' interior, as recently shown by the new seismic and geodetic constraints on Mars' interior obtained by the InSight mission. In the next decade multiple missions will fly to Venus to explore its tectonic and volcanic activity, but they will not be able to conclusively detect seismic waves, despite their potential to detect fault movements. Looking toward the next fleet of Venus missions after the ones already decided, various concepts to measure seismic waves have been proposed. These detection methods include typical geophysical ground sensors already deployed on Earth, the Moon, and Mars; pressure sensors on balloons; and imagers of high altitude emissions (airglow) on orbiters. The latter two methods target the detection of the infrasound signals generated by seismic waves and amplified during their upward propagation. Here, we provide a first comparison between the detection capabilities of these different measurement techniques and recent estimates of Venus' seismic activity. In addition, we discuss the performance requirements and measurement durations required to detect seismic waves with the various detection methods. Our study clearly presents the advantages and limitations of the different seismic wave detection techniques and can be used to drive the design of future mission concepts aiming to study the seismicity of Venus.

Characterizing Sub‐Seafloor Seismic Structure of the Alaska Peninsula Along the Alaska‐Aleutian Subduction Zone

AbstractA shallow sub‐seafloor seismic model that includes well‐determined seismic velocities and clarifies sediment‐crust discontinuities is needed to characterize the physical properties of marine sediments and the oceanic crust and to serve as a reference for deeper seismic modeling endeavors. This study estimates the seismic structure of marine sediments and the shallow oceanic crust of the Alaska‐Aleutian subduction zone at the Alaska Peninsula, using data from the Alaska Amphibious Community Seismic Experiment (AACSE). We measure seafloor compliance and Ps converted wave delays from AACSE ocean‐bottom seismometers (OBS) and seafloor pressure data and interpret these measurements using a joint Bayesian Monte Carlo inversion to produce a sub‐seafloor S‐wave velocity model beneath each available OBS station. The sediment thickness across the array varies considerably, ranging from about 50 m to 2.80 km, with the thickest sediment located in the continental slope. Lithological composition plays an important role in shaping the seismic properties of seafloor sediment. Deep‐sea deposits on the incoming plate, which contain biogenic materials, tend to have reduced S‐wave velocities, contrasting with the clay‐rich sediments in the shallow continental shelf and continental slope. A difference in S‐wave velocities is observed for upper oceanic crust formed at fast‐rate (Shumagin) and intermediate‐rate (Semidi) spreading centers. The reduced S‐wave velocities in the Semidi crust may be caused by increased faulting and possible lithological variations, related to a previous period of intermediate‐rate spreading.

Crustal Heterogeneity of the Bhutan Himalaya: Insights from PgQ Tomography

Abstract We present the results of a seismic investigation conducted in Bhutan using data from the Geodynamics and Seismic Structure of the Eastern Himalaya Region broadband network, focusing on variations in crustal structure and seismic attenuation properties. Through analysis of seismic data from 56 events recorded between 2013 and 2014, with magnitudes exceeding 4.5 and depths shallower than 50 km, we examined 1 Hz PgQ (Q0)-values among multiple station pairs using the two-station method. Our findings reveal significant disparities in PgQ0-values across Bhutan. The western region exhibits low PgQ0 values, indicating high seismic attenuation, whereas the central region shows medium-to-high PgQ0 values, suggesting lower attenuation. Notably, these results are consistent with the geometry of the Moho, providing valuable insights into crustal geometry and rheology. This study contributes to a deeper understanding of Bhutan’s complex crustal structure, offering insights into crustal properties and seismic attenuation mechanisms in this geologically significant region.

WUS324: Multiscale Full Waveform Inversion Approaching Convergence Improves Waveform Fits While Imaging Seismic Structure of the Western United States

AbstractWe report a new model of radially anisotropic crustal and upper mantle structure of the western United States (WUS324) obtained from full waveform inversion of earthquake data. We ran three multiscale inversion stages beyond model WUS256 (Rodgers et al., 2022, https://doi.org/10.1029/2022jb024549) allowing them to approach convergence to fit a larger data set to a shorter minimum period of 16 s. WUS324 is based on 324 total iterations from its starting model, significantly more (16 times) than previous studies. Waveform misfit reductions are 66%–70% for both the inversion data and an independent validation data set providing confidence in the predictive power of the model. WUS324 provides much better fits and reveals shear wavespeed, vS, structure of this large region with more detail than previous waveform tomography models. We show representative images demonstrating the resolution of diverse seismic structure across this highly heterogeneous region including oceanic lithosphere, subducting slabs and continental magmatism.

Integrating Multimodal Deep Learning with Multipoint Statistics for 3D Crustal Modeling: A Case Study of the South China Sea

Constructing an accurate three-dimensional (3D) geological model is crucial for advancing our understanding of subsurface structures and their evolution, particularly in complex regions such as the South China Sea (SCS). This study introduces a novel approach that integrates multimodal deep learning with multipoint statistics (MPS) to develop a high-resolution 3D crustal P-wave velocity structure model of the SCS. Our method addresses the limitations of traditional algorithms in capturing non-stationary geological features and effectively incorporates heterogeneous data from multiple geophysical sources, including 44 wide-angle seismic crustal structure profiles obtained by ocean bottom seismometers (OBSs), gravity anomalies, magnetic anomalies, and topographic data. The proposed model is rigorously validated against existing methods such as Kriging interpolation and MPS alone, demonstrating superior performance in reconstructing both global and local spatial features of the crustal structure. The integration of diverse datasets significantly enhances the model’s accuracy, reducing errors and improving the alignment with known geological information. The resulting 3D model provides a detailed and reliable representation of the SCS crust, offering critical insights for studies on tectonic evolution, resource exploration, and geodynamic processes. This work highlights the potential of combining deep learning with geostatistical methods for geological modeling, providing a robust framework for future applications in geosciences. The flexibility of our approach also suggests its applicability to other regions and geological attributes, paving the way for more comprehensive and data-driven investigations of Earth’s subsurface.

Complicated thermo-chemical heterogeneity of the mantle transition zone beneath the Philippine Sea Plate revealed by SS precursors investigation

The Philippine Sea Plate (PSP), a region renowned for its intricate history of multi-stage subduction and back-arc extension, encounters difficulties in elucidating its deep seismic structure, primarily due to the sparse distribution of seismic stations. This study uses over 44,086 traces of SS precursors collected from >1,000 seismic stations over 10–20 years period, to image the mantle transition zone (MTZ) beneath the PSP. With the curvelet denoising technique, we provide high-resolution maps of the depths of the 410 km (D410) and 660 km (D660) discontinuities and the thickness of the MTZ. Notably, we demonstrate a 10–35 km MTZ thickening extending from the West Philippine Basin to the Shikoku Basin, which may be associated with the thermal effect and dehydration of stagnated slabs in the MTZ. Furthermore, the reflection gap and multiple reflectors were both observed in D410 and D660 beneath the Mariana Trench, which suggests that the vertically subducted Pacific plate transports substantial water and non-olivine components into the MTZ in this area. Additionally, a ∼10–25 km MTZ thinning with an abnormally shallow D660 has been observed beneath the Parece Vela Basin and Caroline Plate in the southern PSP, suggesting the potential existence of thermal upwelling from a secondary plume, which may be possibly the tree branch of the Caroline mantle plume in MTZ. Our results provide new seismological constraints on present and past mantle dynamics in and around the PSP.

Seismic isolation design of high-rise shear wall structures in high-intensity areas

Taking a shear wall structure in a high-intensity area of 20 floors as an example, the seismic reduction scheme of the structure was determined, and the Etabs software was used to conduct time history analysis on the seismic and non-seismic structures. The floor shear force, overturning moment, and short-term surface pressure of the isolation support were obtained. The results showed that under frequent earthquake action, the average maximum floor shear force in the X direction of the isolated upper structure was only about 28 % of that of the non-isolated structure. The maximum inter story shear ratio was 0.34, and the maximum floor shear force in the Y direction was only about 25 % of that of the non-isolated structure. The maximum inter story shear ratio was 0.31. The average maximum overturning moment of the upper structure in the X direction after isolation is about 30 % of that of the non-isolated structure. The maximum overturning moment ratio is 0.36, and the average overturning moment of the maximum floor in the Y direction is about 22 % of that of the non-isolated structure. The maximum overturning moment ratio is 0.26. Under rare earthquake action, the maximum inter story displacement angles in the X and Y directions of each floor of the seismic isolation structure are 1/302 and 1/446, respectively. The maximum surface pressure value of the isolation bearing under rare earthquake is 28.9 MPa, the minimum surface pressure value is 5.58 MPa, and the maximum displacement is 579 mm, which meets the requirements of the specifications. Overall, the seismic performance of the seismic isolation structure is good, and the isolation scheme is feasible.