Journal of Seismology最新文献

The Jiangsu-South Yellow Sea area is located on the East Asian Continental Margin and at the junction of South and North China. It is one of the high seismicity areas in eastern China. To enhance our understanding of the relationship between disastrous earthquakes and the geophysical properties of Earth materials, P- and S-wave travel-time data over the past 20 years are inverted to image the 3D distributions of seismic velocity (V_P and V_s) and Poisson’s ratio (σ). The results show that the velocity and Poisson’s ratio demonstrate congruence with the prominent geological formations present within the study area. Specifically, the velocity models for the upper crust at depths of 5, 10, and 15 km. We found that within the total study area, 70% ± 7.2% of M5+ earthquakes that occurred during the past decades initiated in the V_P tomographic edge zones (TEZ). Moreover, the distribution patterns of M5+ earthquakes in the offshore sea region exhibit significant differences when compared to those in the Jiangnan Orogenic Belt. In the offshore sea region, about 66.7% ± 8% of M5+ earthquakes initiated in the velocity and Poisson’s ratio TEZ. The presence of comparatively low V_s and high Poisson’s ratio anomalies in the Wunansha Uplift suggest the potential existence of fluids. The triggering mechanism for these earthquakes can likely be ascribed to the presence of hydrothermal fluids and the reactivation of preexisting strike-slip faults, influenced by the subduction of the Pacific and Philippine Sea Plates, as well as the collision between the India and Eurasia Plates. In contrast, within the Jiangnan Orogenic Belt, M5+ earthquakes predominantly initiated in the high-velocity and low Poisson’s ratio perturbation zones. The primary factor contributing to seismotectonic features disparities are likely the variation in fluid content. We infer the rock matrix in the vicinity of the source region of the Jiangnan Orogenic Belt is presumed to be drier, more brittle, and possess greater mechanical strength.

Near-source ({kappa }_{s}), along-path (widetilde{kappa }), and near-site ({kappa }_{0}) contributions to the spectral parameter kappa ((kappa)) were studied from earthquakes located along the Canal de Ballenas-Guaymas fault system and recorded by stations sited around the central-north Gulf of California, Mexico. The dataset consists of 26 earthquakes (M 3.4-6.0) recorded by six stations with hypocentral distances ranging from 31 to 270 km. We used the Anderson and Hough (1984) approach to estimate (kappa), followed by a one-step least-squares inversion to separate (kappa) contributions. We found that (kappa) has a range of 0.0260 to 0.1012 s, with a mean of 0.0600 (pm) 0.0170 s, while ({kappa }_{s}) and ({kappa }_{0}) exhibit means of 0.0088 (pm) 0.0059 s and 0.0200 (pm) 0.0205 s, respectively. We also observed significant inter-event ({kappa }_{s}) and inter-station ({kappa }_{0}) variabilities. The (dwidetilde{kappa }/dr) regional average is 0.00023 (pm) 0.00001 s, equivalent to a regional quality factor of 1242 (pm) 54 for an S-wave velocity of 3.5 km/s. Furthermore, our results suggest that (dwidetilde{kappa }/dr) tends to decrease with distance. We demonstrate that a well-designed least-squares inversion scheme can effectively address the limitations associated with estimating ({kappa }_{0}) using the Anderson and Hough approach in situations where recordings per station have a narrow distance range and where no recordings at small source-site distances are available for most stations. We found no correlation of ({kappa }_{s}) with earthquake magnitude. Instead, relatively higher ({kappa }_{s}) values tend to cluster along the ridge flanks of the Canal de Ballenas Basin, where hydrothermal fluid circulation is expected.

Rock burst is one of the major disasters that endanger coal safety production. If a rock burst occurs, it will cause terrible casualties and significant property losses. Therefore, this article proposes to predict the sensitive characteristics of microseisms, which can achieve the prediction and early warning of rock burst disasters to a certain extent. To effectively improve the prediction accuracy and robustness of microseismic sensitive feature data, a hybrid model called VMD-Transformer is suggested in this study for predicting time series of microseismic sensitive features. This model is based on the variational mode decomposition (VMD) and transformer model and aims to predict future eigenvalue from the historical data of sensitive features. To a certain extent, the transformer model is used to predict the future eigenvalue, while the VMD is used to extract the features of the time series data at various frequency domain scales, which solves the problem of non-stationary time series data being difficult to predict accurately due to high fluctuations. This study extracts sensitive features from microseismic events that the same source registered by a certain geophone after locating, decomposes the time series of the sensitive features using VMD, predicts each component of the decomposition separately using the transformer model, and then combines the component prediction results to produce the final prediction results. Experimental results indicate that our method has the features of a simple algorithm, strong adaptivity, and high prediction accuracy and can effectively predict time series of sensitive features extracted from microseismic signals.

Using the three component acceleration records of the National Strong Motion Observation Network System (NSMONS) and the National Seismic Intensity Rapid Reporting and Earthquake Early Warning Network, the ground motion attenuation characteristics, spatial distribution, source rupture direction, and near-fault pulse characteristics of the Luding M_S6.8 earthquake were analyzed. Comparing the observed values of peak ground acceleration (PGA), peak ground velocity (PGV), pseudo-spectral acceleration (PSA), and 90% significant duration (SD) with several typical ground motion prediction equations (GMPE), it was found that the ground motion attenuation characteristics of this earthquake are consistent with GMPE for the southwest region, but overall lower than the global model average level. In the comparison of between-event residuals, this earthquake exhibits different characteristics from the same magnitude thrust type earthquake. The within-event residuals reflect that the anelastic attenuation in the Luding region is slightly weaker than that in the Menyuan region. In terms of spatial distribution of ground motion parameters, the PGV and PSA with a period of 1.0 to 8.0 s have significantly higher intensity in the southeast direction of the epicenter than in other directions. Based on PGV, it is speculated that the source rupture direction of the earthquake was 151°, which is close to the fault strike of 163°. Pulse-like ground motions were identified in up to 12 sets of near-fault records with pulse periods significantly lower than historical earthquakes of similar magnitudes. Stations with pulse peak values greater than 40 cm·s⁻¹ in the pulse dominant direction of the velocity time history all appeared in the narrow band area ahead of the rupture direction. The distribution area of near-fault pulses is highly correlated with the distribution of high macroseismic intensity areas and landslide areas, and it is necessary to pay attention to the impact of near-fault pulses in seismic fortification.

Strong pulse-like ground motions excited by a causative fault with a rupture propagation close to the shear wave velocity can induce significant earthquake hazards. The single original and horizontal rotation components of pulse-like ground motion were mainly considered in the last years, especially the generation mechanism of velocity pulse and its influence on engineering structures. Conversely, less attention is paid to the vertical component in such seismic events, so that the identification of pulses in arbitrary direction of space from multi-component motion is neglected. Furthermore, although extensive seismic record data have been obtained with the improvement of observation equipment and analysis technology, there are still few strong motion records carrying velocity pulse waveform. In order to obtain more pulse records and expand the range of pulse identification within limited strong motion data, we describe a spatial rotation technique to determine the velocity pulse in arbitrary direction from the three orthogonal components of ground motion. In this paper, the strong ground motions of 46 seismic events are processed, and the strongest velocity pulse is identified and extracted based on continuous wavelet transform. The extracted time history of the long-period velocity pulse is well matched with the rotated seismic record. To better represent the seismic hazard, we quantify the spatial pulse and spectral parameters that characterize pulse-like ground motion. The results indicate that velocity pulse-like motion exhibits marked systematic distribution characteristics, the spatially rotated component of ground motion is significantly larger than the strongest original and horizontal records, and the spatial orientation of velocity pulse is affected by various geological factors. This study supplements the long-period velocity pulse data and increases the pulse peak threshold range. The acceleration amplification factor is 1.2 times the seismic code value, especially the higher magnification values of velocity and acceleration occur in stiff soil and soft rock sites. The peak ratio of seismic ground motion increases with increasing hypocenter distance, which reflects that the attenuation of ground motion velocity is slower than that of motion acceleration. Thus, by combining the moment magnitude, source-site geometry, and site conditions, we provide a quantitative framework to better assess and simulate pulse-like ground motion in seismogenic regions.

Zagros, on the Alpine-Himalayan belt, has undergone significant tectonic tension due to the convergence of the Arabian and Eurasian plates, resulting in numerous faults, folds, and thrusts. Despite extensive research, uncertainties persist regarding its seismotectonic features and active faults. This study aims to identify causative faults for earthquakes within this region by calculating focal mechanisms of 47 earthquakes that occurred in northwest Zagros and examining seismicity at depth. In this pursuit, 12 cross-sections have been delineated within the region. The spatial distribution of earthquakes within these sections, coupled with the computed focal mechanisms, serves as indicators of the causative fault. The study attributes a significant proportion of the recorded earthquakes to different segments of the Mountain Front Fault and estimates the length of some segments to exceed what is depicted in geological maps. Clear trends in the depth distribution of earthquakes and alignment of some features with previous studies suggest the activity of hidden faults and the influence of an arc in the study area. The collective results provide a comprehensive understanding of the proposed arc, further reinforced by the identification of a strike-slip fault intersecting the High Zagros Fault, serving as tangible evidence of the arc’s existence.

For an ω²-source model, moment-based estimates of the stress drop are obtained by combining corner frequency and seismic moment source parameters. Therefore, the moment-based estimates of the stress drop are informative about the amount of energy radiated at high frequencies by dynamic rupture processes. This study aims to systematically estimate such stress drop from the harmonized dataset at the European scale and to characterize the distributions of the stress drop for application in future stochastic simulations. We analyze the seismological records associated with shallow crustal seismic events that occurred in Western Europe between January 1990 and May 2020. We processed 220,000 high-quality records and isolated the contributions of the source, site, and path contributions using the Generalized Inversion Technique. The source parameters, including the corner frequency, moment magnitude, and stress drop, of 6135 seismic events are calculated. The events processed are mainly tectonic events (e.g., earthquakes of the central Italy 2009–2016 sequence), although non-tectonic events associated with the Groningen gas field and mining activities in Western Europe are also included in the analysis. The impact of different attenuation models and reference site choices are evaluated. Most of the obtained source spectra follow the standard ω²-model except for a few events where the data sampling considered does not allow an effective spectral decomposition. The resulting stress drop shows a positive correlation with moment magnitude between 3 and 4, and a self-similarity for magnitudes greater than 4 with a mean stress drop of 13.8 MPa.

We study the strong 12 October 2021, (M_W)=6.4, offshore Zakros, Crete earthquake, and its seismotectonic implications. We obtain a robust location (azimuthal gap equal to 17(^{circ })) for the mainshock by combining all freely available local, regional and teleseismic phase arrivals (direct and depth phase arrivals). Based on our location and the spatial distribution of the poor aftershock sequence we parameterise the fault area as a 30 km (times ) 20 km planar surface, and using three-component strong motion data we calculate slip models for both earthquake nodal planes. Our preferred solution shows a simple, single slip episode on a NE-SW oriented, NW shallow-dipping fault plane, instead of a N-S oriented, almost vertical nodal plane. An anti-correlation of the aftershocks spatial distribution versus the maximum slip ((sim ) 27 cm) of our model further supports this, although the accuracy of the aftershock hypocentral locations could be somewhat questionable. Coulomb stress changes calculated for both kinematic models do not show substantial differences, as the aftershock seismicity within the first 3 months after the mainshock is distributed along the stress shadow zone and over the stress enhanced areas developed at the southern fault edge, induced by the mainshock. The Kasos island tide gauge record analysis shows a small signal after the earthquake, but it can hardly demonstrate the existence of tsunami waves due to the low signal-to-noise ratio. Tsunami simulations computed for the two nodal planes do not yield conclusive evidence to highlight whether the causative fault plane is NE-SW oriented, NW shallow-dipping plane, or the N-S oriented plane, nevertheless, the power spectrum analysis of the NW shallow-dipping nodal plane matches the spectral peak at 8 s period and is overall closer to the spectrum of the tide gauge record. A USGS Shakemap was also produced with all available local strong motion data and EMSC testimonies. This was also investigated in an effort to document the responsible fault. The overall analysis in this study, slightly suggests a rather westward, shallow-dipping offshore fault zone, being antithetic to the main Zakros almost vertical normal fault which shapes the coast of eastern Crete and is perpendicular to the direction of Ptolemy Trench in this area. This result agrees with seismotectonic and bathymetric evidence which support the existence of approximately N-S trending grabens, east and northeast of Crete.

The 14 April 1895 (Mw 6.1, in the area of Ljubljana, Slovenia) earthquake is still not fully understood. The aim of this work is to derive information about its source from the inversion of an updated dataset of intensities (evaluated with EMS-98). This was done via automatic non-linear geophysical inversion KF-NGA, which was performed using a Niching Genetic Algorithm and has been presented in other articles. The distribution of damage caused by this earthquake is not homogeneous and often shows significant intensity differences between neighbouring sites. Statistical analysis of the intensities, epicentral distances and geologic nature of the sites suggests some site effects. Nevertheless, the resulting solution is consistent with regional seismotectonics, i.e. an almost pure dip-slip mechanism: strike 282° ± 5°, dip 38° ± 7°, rake 86° ± 9° (± 180° because of the intrinsic ambiguity of the KF-NGA-inversion). Since the rake angle is close to 90°, there is an almost perfect ambiguity between the two planes of the focal mechanism. Therefore, our solution has a Dinaric direction and could be associated either with a fault plane that dips NE or with one that dips SW.

The 2017 Malard and 2020 Damavand moderate crustal earthquakes (M_w 4.8) occurred about 40 km west and about 55 km northeast of Tehran, the capital and economic heart of Iran, with a metropolitan population of over 15 million. Seismic hazard assessment in the region has been affected by few historically documented destructive earthquakes with magnitudes around 7.0 (e.g., 312–280 B.C, 958, 1177, and 1830 A.D.); however, in the absence of large contemporary earthquakes, a detailed analysis of moderate earthquakes is essential. In this study, seismic sources of the two earthquakes are characterized in terms of focal mechanism, fault geometry, and rupture directivity through waveform inversion, hypocenter relocation, and empirical Green’s function methods. The eastern segment of the well-known Mosha fault is responsible for the 2020 Damavand earthquake, with a left-lateral strike-slip mechanism ruptured unilaterally westward where Tehran is situated. The 2017 Malard earthquake is a peculiar case in a poorly studied region. For this event, we propose a left-lateral strike-slip mechanism corresponding to E-W trending Mahdasht fault. This event was preceded by a swarm of events, 12 km northward, that started a few months earlier and terminated right before the mainshock. The energy released due to this precursory activity was higher than the Malard mainshock and its aftershocks. The events seem to align along an N-S transverse basement fault that, further southward, may intersect with the Mahdasht fault system.