Search Results (47)

Petit-spot volcanism is a type of intraplate volcanism that commonly occurs near the outer rise in subducting plates. Although deformation of the incoming plate is considered important for its development, the deeper mantle processes contributing to this volcanism remain poorly understood. Here, we use more than 1500 broadband seismograms containing long-period SS precursors to investigate the mantle transition zone (MTZ) beneath the Sunda–Java subduction system. Beneath the northern Sunda–Java region, the 660 km discontinuity (d660) reaches ~690 km depth, resulting in an MTZ thicker than 270 km, consistent with the thermal influence of the subducted Indo-Australian slab. The associated weakening of S660S amplitudes may reflect hydration or other factors affecting the lower MTZ. South of the trench, the MTZ beneath most of the Christmas Island Seamount Province is relatively uniform, with a thickness of ~251 km. Beneath Christmas Island, however, the 410 km discontinuity (d410) is depressed to ~420–425 km, whereas d660 remains near 670–675 km, producing a localized thinner MTZ of ~245–250 km. This structure is compatible with localized slab-related mantle processes and may reflect thermal or compositional heterogeneity near the top of the MTZ. Although our observations do not directly resolve volatile transport or melt generation, they provide new constraints on the deep-mantle environment associated with rejuvenated petit-spot volcanism at Christmas Island. Full article

This research proposes a physics-based deep learning framework, developed as a proof-of-concept based on synthetic data, for estimating the mechanical properties of layered media—namely density (ρ), Young’s modulus (E), and top layer thickness (h₁)—using synthetic seismogram images generated via Finite Element Method (FEM) simulations. The dataset, comprising 5000 simulations, incorporates physical constraints and empirical density–modulus correlations. While a ResNet-style Convolutional Neural Network (CNN) extracts density and stiffness parameters from composite time–frequency images, the estimation of h1 utilizes a direct time-domain raw-signal approach to preserve spatial resolution. A 5-fold nested cross-validation scheme with internal Bayesian Optimization ensures rigorous model evaluation, further validated by normality assessments and bootstrap confidence intervals. Performance was tested against synthetic Gaussian noise (0% to 50%) and benchmarked against classical Full Waveform Inversion (FWI). The results demonstrate high predictive accuracy for shallow properties, with R² values reaching 0.96 for Young’s modulus and 0.83 for raw-signal thickness. The neural network model requires 0.035 s per inference compared to 180 s for the FWI approach, avoiding the local minima convergence issues typical of iterative inversion. The framework exhibits resilience under moderate noise levels (up to 30%), establishing a reliable baseline for future experimental validation. Full article

Seismic Shake-e is a free app that provides valuable data and tools related to earthquakes, covering the stages before, during, and after seismic events. In this text, we describe the main features of the Seismic Shake-e 2.1 (SSe) app, the considerations that guided its development, examples of its use, and the challenges for future versions. Version 1.0 of this app was awarded as one of the winners of EOVALUE: Call for Innovative Apps in environmental and social fields, a project by the Joint Research Centre (JRC), the European Commission’s science and knowledge service. SSe recognizes two user levels: basic and intermediate/advanced. There are six modules for each level. The main topics of these modules for both user types are: (1) Accelerometer Networks (AN), (2) Seismograms Analyzer-e (SAe), (3) Seismic Design of Buildings (SDB), (4) Earthquake Preparedness (EP), (5) Earthquake Early Warning Systems (EEWS) & Tsunami Warning Systems (TWS), and (6) Earthquake Emergency Response & Recovery. The two key modules are AN and SAe: the first explains how to obtain seismic records, and the second provides tools for their analysis. We include some applications of SSe, along with their results and discussion. We also list the advantages of the main modules and discuss potential future developments and improvements. The uniqueness of this work is that we highlight the software’s essential features and demonstrate its applications. Full article

The structural characteristics of the Majiatan fault–fold system in the northwestern Ordos Basin are complex, and the detailed 3D distribution of faults and their evolutionary mechanisms remain insufficiently understood, which restricts effective petroleum exploration in this region. To address this, this study utilizes high-resolution 3D seismic data comprising 20 lines (total length 753.371 km, survey grid 3 × 3 km) and drilling and logging data from 13 wells (including synthetic seismograms) to establish a detailed 3D fault model. We aim to elucidate the fault styles and the formation mechanism of the fault–fold–thrust belt. Results indicate the presence of 47 Mesozoic faults, all of which are thrust faults classified into three types. Structural traps dominate the leading transition zone, whereas lithologic–structural traps are prevalent in the Tian-huan Syncline. Laterally, from south to north, the fault occurrence transitions from west-dipping east-thrust to east-dipping west-thrust, accompanied by a shift in tectonic style from thrusting nappe to late-stage reconstruction. The stress intensity generated during the Late Cretaceous increases northward, causing deformation to shift westward. Typical fault styles observed include “y-shaped”, “flower-shaped”, and “imbricated” structures. The middle-north zones of the Majiatan area and the Hengshanbu Thrust Belt share a unified formation mechanism: initiation in the Late Triassic, main development in the Late Jurassic, initial shaping in the Late Cretaceous, and final modification in the Eocene, driven by the rotation of the Ordos Basin and shear tectonic forces. The most favorable exploration zones are identified at the junctions between the leading zone, the fault–fold zone, and weakly transformed zones. The tectonic evolution model established in this study provides a valuable reference for understanding structural complexities and guiding hydrocarbon exploration in similar fold and thrust belts globally. Full article

Due to the fact that earthquakes cannot be predicted, earthquake simulation is of great importance. An earthquake simulator is a device that reproduces the seismic waves generated by an earthquake. The aim of this work is to present the design and prototyping of an earthquake simulator that simulates a real long-period ground motion earthquake with vertical displacement, according to the earthquake seismogram. A control interface was designed for a prototype earthquake simulator to reproduce a given earthquake seismogram. The mobile platform of the earthquake simulator prototype performs translational motions in the direction of the X and Y axes due to the use of a cable-driven parallel robot, and the vertical translational motion of the platform along the Z axis is performed by linear screw drives. A prototype earthquake simulator was manufactured and tested, confirming the feasibility of reproducing long-period ground motion during an earthquake. The earthquake simulator implements motions that make a person experience sensations similar to those that occur during real earthquakes. Full article

This work aims to develop approaches to processing and interpreting spectral entropy outcomes in the context of seismic data, as well as to establish a methodological foundation for subsequent integration into practical monitoring solutions. The objective of this study is to evaluate the effectiveness of the Shannon spectral entropy method in detecting and assessing short-term seismic events through a seismogram analysis. This method has demonstrated sensitivity to variations in the spectral characteristics of the registered signals. A threshold value for the increase in spectral entropy information has been pinpointed for reliable P-wave detection. The results could be applied in real-time automated seismic monitoring systems. In addition to the conventional spectral analysis techniques, the proposed methodology may serve as the input to the neural network models used in seismological applications. Full article

Following the abrupt geochemical and geophysical variations that occurred on the island of Vulcano in September 2021, the search for previous multidisciplinary data on decades-long time spans became necessary to contextualize the newly recorded anomalous variations, which represented a serious threat for the local population. Our analyses of ‘vintage’ reports, old documents and analogue seismograms, broaden our understanding of crustal seismic activity. The results unravel the predominant role of Vulcano’s hydrothermal system with respect to tectonic processes in the generation of seismicity in the analyzed sector. Earthquakes were generally located offshore and achieved a maximum M4.6. A 2D strain release map and DBSCAN application highlight seismogenic volumes to the NW, SW and E offshore of the island and trending NNW-SSE inshore, in agreement with structural patterns. Two major volcano unrests in 1985 and 1988 had seismicity mostly confined to the island. In comparison, the longer duration and typology of seismic signals recorded between 2021 and 2022 make this latest episode peculiar in the context of Vulcano’s past seismic activity. Full article

The Himalayan belt, formed due to the Cenozoic convergence between the Eurasian and Indian craton, acts as a storehouse of large amounts of strain, resulting in large earthquakes from the Western to the Eastern Himalayas. Glaciers also occur over a major portion of the high-altitude Himalayan region. The impact of earthquakes can be easily studied in the plains and plateaus with the help of well-distributed seismogram networks and these regions’ accessibility is helpful for field- and lab-based studies. However, earthquakes triggered close to high-altitude Himalayan glaciers are tough to investigate for the impact over glaciers and glacial deposits. In this study, we attempt to understand the impact of earthquakes on and around Himalayan glaciers in terms of vertical displacement and coherence change using space-borne synthetic aperture radar (SAR). Eight earthquake events of various magnitudes and hypocenter depths occurring in the vicinity of Himalayan glacial bodies were studied using C-band Sentinel1-A/B SAR data. Differential interferometric SAR (DInSAR) analysis is applied to capture deformation of the glacial surface potentially related to earthquake occurrence. Glacial displacement varies from −38.9 mm to −5.4 mm for the 2020 Tibet earthquake (M_w 5.7) and the 2021 Nepal earthquake (M_w 4.1). However, small glacial and ground patches processed separately for vertical displacements reveal that the glacial mass shows much greater seismic displacement than the ground surface. This indicates the possibility of the presence of potential site-specific seismicity amplification properties within glacial bodies. A reduction in co-seismic coherence around the glaciers is observed in some cases, indicative of possible changes in the glacial moraine deposits and/or vegetation cover. The effect of two different seismic events (the 2020 and 2021 Nepal earthquakes) with different hypocenter depths but with the same magnitude at almost equal distances from the glaciers is assessed; a shallow earthquake is observed to result in a larger impact on glacial bodies in terms of vertical displacement. Earthquakes may induce glacial hazards such as glacial surging, ice avalanches, and the failure of moraine-/ice-dammed glacial lakes. This research may be able to play a possible role in identifying areas at risk and provide valuable insights for the planning and implementation of measures for disaster risk reduction. Full article

Dynamic rupture simulations of earthquakes offer crucial insights into the physical mechanisms of driving fault slip and seismic hazards. By incorporating non-planar fault models that accurately represent subsurface structures, this study provides a realistic depiction of the rupture processes of the 2020 Mw 6.8 Elazığ, Türkiye earthquake, influenced by geometric complexities. Initially, we determined its coseismic slip on the non-planar fault using near-field strong motion and InSAR observations. Subsequently, we established the heterogeneous initial stress on the fault plane based on the coseismic slip and integrated it into the dynamic rupture modeling to assess physics-based ground motion and seismic hazards. The numerical simulations utilized the curved grid finite-difference method (CGFDM), which effectively models rupture dynamics with heterogeneities in fault geometry, initial stress, and other factors. Our synthetic surface deformation and seismograms align well with the observational data obtained from InSAR and seismic instruments. We observed localized occurrences of supershear rupture during fault propagation. Furthermore, the intensity distribution we simulated closely aligns with the actual observations. These findings highlight the critical role of source heterogeneity in seismic hazard assessment, advancing our understanding of fault dynamics and enhancing predictive capabilities. Full article

We observed high-quality waves from a repeatable airgun seismic source recorded by a linear ultra-dense seismic array across the Xiliushui fault zone, one of the inactive faults in the Qilian Mountain, on the northeastern margin of the Tibetan Plateau, China. We used Snell’s law of seismic ray propagation to determine a simplified ambient velocity model. Based on the flexible and precise spectral element method, we computed broadband synthetic seismograms for a shallow low-velocity fault zone (FZ) to model the direct P-wave travel time delay and incident angle of the wavefield near the FZ. The FZ extent range and boundaries were inverted by apparent travel time delays and amplification patterns across the fault. According to prior information on the properties of the direct P-waves, we could constrain the inverse modeling and conduct a grid search for the fault parameters. The velocity reduction between the FZ and host rock, along with the dip angle of the FZ, were also constrained by the P-wave travel time delay systematic analysis and incoming angle of the P-waves. We found that the Xiliushui fault has a 70~80 m-wide low-velocity fault damage zone in which the P-wave velocity is reduced to ~40% with respect to the host rock. The fault damage zone dips ~35°southwest and extends to ~165 m in depth. The repeatability and environment protection characteristics of the airgun seismic survey and the economic benefits of a limited number of instruments setting are prominent. Full article

It is challenging to apply the receiver function method to teleseisms recorded by ocean-bottom seismographs (OBSs) due to a specific working environment that differs from land stations. Teleseismic incident waveforms reaching the area beneath stations are affected by multiple reflections generated by seawater and sediments and noise resulting from currents. Furthermore, inadequate coupling between OBSs and the seabed basement and the poor fidelity of OBSs reduce the signal-to-noise ratio (SNR) of seismograms, leading to the poor quality of extracted receiver functions or even the wrong deconvolution results. For instance, the poor results cause strong ambiguities regarding the Moho depth. This study uses numerical modeling to analyze the influences of multiple reflections generated by seawater and sediments on H-kappa stacking and the neighborhood algorithm. Numerical modeling shows that seawater multiple reflections are mixed with the coda waves of the direct P-wave and slightly impact the extracted receiver functions and can thus be ignored in subsequent inversion processing. However, synthetic seismograms have strong responses to the sediments. Compared to the waveforms of horizontal and vertical components, the sedimentary responses are too strong to identify the converted waves clearly. The extracted receiver functions correspond to the above influences, resulting in divergent results of H-kappa stacking (i.e., the Moho depth and crustal average V_P/V_S ratio are unstable and have great uncertainties). Fortunately, waveform inversion approaches (e.g., the neighborhood algorithm) are available and valid for obtaining the S-wave velocity structure of the crust–upper mantle beneath the station, with sediments varying in thickness and velocity. Full article

Noise reduction is a critical step in seismic data processing. A novel strong noise reduction network is proposed in this study. The network enhances the U-Net architecture with an improved inception module and coordinate attention (CA) mechanism, suppressing noise and enhancing signal clarity. These enhancements improve the network’s capability to distinguish between signal and noise in the time–frequency domain. We trained and tested our model on the STEAD dataset, which eliminated noise across various frequency bands, improved the signal-to-noise ratio (SNR) of seismic records, and reduced the waveform distortion significantly. Comparative analyses against U-Net, DeepDenoiser, and DnRDB models, using signals with SNRs ranging from −14 dB to 0 dB, demonstrated our model’s superior performance. At the same time, we demonstrated that the Inception Conv Block has a significant impact on the denoising ability of the network. Furthermore, validation using the “Di Ting” dataset and real noisy signals confirmed the model’s generalizability. These results show that the proposed model significantly outperforms the comparative methods in terms of the SNR, correlation coefficient (r), and root mean square error (RMSE), delivering higher-quality seismograms. The enhanced phase-picking accuracy underscores the potential of our approach to advance in geophysics applications. Full article

Numerical modeling of acoustic-elastic media is helpful for seismic exploration in the deepwater environment. We propose an algorithm based on the staggered grid finite difference to simulate wave propagation in the interface between fluid and transversely isotropic media, where the interface does not need to consider the boundary condition. We also derive the stability conditions of the proposed method. Scholte waves, which are generated at the seafloor, exhibit distinctly different propagation behaviors than body waves in ocean-bottom seismograms. Numerical examples are used to characterize the wavefield of Scholte waves and discuss the relationship between travel time and the Thomsen parameters. Thomsen parameters are assigned clear physical meanings, and the magnitude of their values directly indicates the strength of the anisotropy in the media. Numerical results show that the velocity of the Scholte wave is positively correlated with ε and negatively correlated with δ. And the curve of the arrival time of the Scholte wave as a whole is sinusoidal and has no symmetry in inclination. The velocity of the Scholte wave in azimuth is positively related to the polar angle. The energy of the Scholte wave is negatively correlated with the distance from the source to the fluid-solid interface. The above results provide a basis for studying oceanic Scholte waves and are beneficial for utilizing the information provided by Scholte waves. Full article

Fully coupled soil–structure analyses were performed for a building of strategic importance located in the city of Messina (Sicily, Italy). The structure was built after the destructive 1908 earthquake, also known as the ‘Messina and Reggio Calabria earthquake’, which caused severe ground shaking. A parametric study considering three seismograms of this earthquake was performed. Deep in situ and laboratory investigations allowed the definition of the geometric and geotechnical model of the subsoil. Numerical analyses were performed with PLAXIS3D finite element software (Version 21.01.00.479). The Hardening Soil model with small-strain stiffness was accurately calibrated using laboratory and field data. The dynamic response was investigated in terms of accelerations, response spectra, amplification functions, displacements and stress–strain hysteretic loops. The findings show that many aspects must be investigated for the retrofitting of buildings with shallow foundation in areas characterized by a medium to high level of seismic risk: (i) a key role is played by an accurate investigation of the soil; taking into account the specific conditions of the soil, it was possible to investigate its filtering effects; (ii) the dynamic response of the fully-coupled soil–structure system deviates from the free field-site response analysis; (iii) the results reveal the importance of considering the soil nonlinearity in seismic soil–structure interaction problems. Full article

Q-compensated reverse time migration (Q-RTM) is a crucial technique in seismic imaging. However, stability is a prominent concern due to the exponential increase in high-frequency ambient noise during seismic wavefield propagation. The two primary strategies for mitigating instability in Q-RTM are regularization and low-pass filtering. Q-RTM instability can be addressed through regularization. However, determining the appropriate regularization parameters is often an experimental process, leading to challenges in accurately recovering the wavefield. Another approach to control instability is low-pass filtering. Nevertheless, selecting the cutoff frequency for different Q values is a complex task. In situations with low signal-to-noise ratios (SNRs) in seismic data, using low-pass filtering can make Q-RTM highly unstable. The need for a small cutoff frequency for stability can result in a significant loss of high-frequency signals. In this study, we propose a multi-task learning (MTL) framework that leverages data-driven concepts to address the issue of amplitude attenuation in seismic records, particularly when dealing with instability during the Q-RTM (reverse time migration with Q-attenuation) process. Our innovative framework is executed using a convolutional neural network. This network has the capability to both predict and compensate for the missing high-frequency components caused by Q-effects while simultaneously reconstructing the low-frequency information present in seismograms. This approach helps mitigate overwhelming instability phenomena and enhances the overall generalization capacity of the model. Numerical examples demonstrate that our Q-RTM results closely align with the reference images, indicating the effectiveness of our proposed MTL frequency-extension method. This method effectively compensates for the attenuation of high-frequency signals and mitigates the instability issues associated with the traditional Q-RTM process. Full article