Journal of Seismology最新文献

The northeastern region of Algeria is renowned for its significant seismic activity within the North African context. The high seismicity rate in this area can generate a high level of earthquake hazard, emphasizing the pressing need for a reliable seismic hazard assessment to design structures capable of withstanding such catastrophic events. In fact, conducting a seismic hazard assessment, achievable through deterministic or probabilistic methods, requires a comprehensive, updated, unified earthquake dataset. This dataset serves as the primary and essential information source for delineating seismic source zones and comprehensively characterizing them. Accordingly, the main objective of this study is to conduct an improved Probabilistic Seismic Hazard Assessment (PSHA) for the northeast region of Algeria, spanning 35°–37° N latitude and 4°–8,5° E longitude, while establishing a unified earthquake catalog for the region in terms of moment magnitude scale (M_w). New data from national and international agencies and findings from recent scientific publications inform the development of a unified seismicity catalog with the least amount of uncertainties. Subsequently, the catalog is declustered to filter out foreshocks and aftershocks from the earthquake data. This refined catalog is used to delineate five seismic zones and to estimate the seismicity parameters for each seismic source zone. For the seismic hazard calculations, three suitable Ground Motion Prediction Equations (GMPEs) are used for the area under study. The code (REASSESS V2.0), a new software for single and multi-site PSHA, was used to carry out the seismic hazard analysis for the area under study. The PSHA was performed using a standard logic tree methodology, allowing for a systematic consideration of model-based uncertainties and their effects on the estimated ground motion parameters. The hazard is quantified in terms of peak ground acceleration (PGA), short-period (0.2 s), and long-period (1s) spectral acceleration maps, as well as uniform hazard spectra for return periods of 100 and 475 years. The outcomes gained from this study are anticipated to significantly contribute to future land-use planning and the development of facilities and infrastructure in the region.

This paper focuses on a study of the source of the Morocco September 8, 2023, earthquake (M_w= 6.9) using seismic and geodetic data. We have used 46 P-wave and 11 S-wave teleseismic data to obtain a model of a kinematic extended seismic source. The rupture occurred on a near-vertical plane dipping 67° to the NNW and striking 247°, with a thrusting motion with a strike-slip component (rake=73°). The rupture was 10s, with the maximum energy released at the first 3, and the rupture occurred at 24 km depth, which doesn’t reach the surface, stopping approximately at 12 km depth. The slip distribution is an elliptical patch of an area of 568 km², a maximum slip of 2.6 m and a scalar seismic moment of 2.5 x 10¹⁹ Nm. The radiated seismic energy is 5.4 x 10¹⁴ J, stress drop 4 MPa and apparent stress 0.98 MPa. Synthetic ground deformations obtained from the source model agree with DInSAR observed deformations, showing a maximum uplift of 16.4 cm and subsidence of 4.2 cm. This study enhances understanding of stress accumulation and release processes in the High Atlas and contributes to a better seismic risk assessment in the area, and highlighting that low seismicity zones are not immune to large, destructive earthquakes.

Ground motion prediction equations (GMPEs) are effectively used in seismic hazard analysis to estimate peak ground accelerations (PGAs). They exhibit reduced accuracy when applied to a wide range of earthquake magnitudes and hypocentral distances, as they are often developed using datasets with limited coverage of extreme values. This study employs machine learning (ML) techniques to develop a region-specific ground motion model (GMM) for north and northeast India, capable of determining PGA accurately over a broader range of seismic source parameters. This study evaluates the performance of four widely used ML models, namely random forest (RF), extreme gradient boosting (XGB), support vector regression (SVR), and artificial neural network (ANN), to determine the most suitable approach for predicting the PGA. A dataset of 445 recorded ground motion records from 116 earthquake events is used to train and test the models. The RF model achieved the highest predictive performance with a coefficient of determination (R²) value of 0.9056. The performance indices further confirm the superiority of the RF model over the traditional GMPEs and GMMs.

On December 27, 2022, a moderate earthquake (M_L = 5.0) struck the western coast of the Gulf of Suez at 28.03° N and 33.47° E. The event was felt up to 500 km away and was recorded by the Egyptian National Seismological Network (ENSN) and the Egyptian National Strong Motion Network (ENSAN). The epicenter was located about 53 km from a previous M_L = 5.1 earthquake that occurred in June 2013. This study determines the source parameters, focal mechanism, and moment tensor of the December 27, 2022 earthquake to better understand its rupture characteristics and tectonic context. Displacement spectra were analyzed to estimate the long-period spectral level and corner frequency, from which the seismic moment was derived (1.96 × 10²⁰–1.44 × 10²² dyne·cm) and converted to moment magnitude. The estimated source radius ranged from 136 to 254 m, with stress drop values between 2.3 MPa and 61.3 MPa. The corner frequency, inversely related to rupture duration, varied from 5.2 Hz to 9.8 Hz. Moment tensor analysis of the mainshock and three aftershocks (M_L ≈ 4.0) revealed predominantly normal faulting with minor strike-slip components, aligned mainly along NNW–SSE and NW–SE directions. This mechanism is consistent with the regional tectonic framework and previously reported fault structures of the Gulf of Suez. The results contribute valuable information for updating seismic hazard assessments in this economically strategic region.

In this research, we used the 2006–2024 seismic catalog from the Iranian Seismological Center for a comprehensive analysis of the seismicity parameters (b -value, the magnitude of completeness (M_C), Fractal Dimension (D_C), Seismic Moment (M₀), and seismic quiescence (Z -value)) in the vicinity of Mw 6.2 Murmuri Earthquake of August 18, 2014, in the Zagros region of Iran. The M_C exhibits spatial heterogeneity, with values ranging from 2.0–2.5 near Dehloran to 3.0–3.5 near the Mountain Front Fault (M.F.F.), reflecting detection challenges in complex fault zones. Spatial b -value distribution indicates low values near the mainshock epicenter and M.F.F., suggesting high-stress accumulation. The D_C -value shows higher values near the epicenter, reflecting clustered seismicity. An orthogonal regression analysis reveals a strong negative correlation (r = -0.71) between b-value and D_C -value in the region. The Z -value distribution in early 2014, using a 2-year time window, identifies significant quiescence near the epicenter, a precursor to the mainshock, transitioning to post-event activation. The spatial distribution of Z -values exhibits a complex pattern, with lower values (z ≈ − 1.0 to − 1.5) concentrated near the Murmuri epicenter, indicating a moderate decrease in seismic activity relative to the reference period. These findings highlight the M.F.F. as a high-hazard zone, with integrated parameter analysis enhancing precursory detection and post-event stress mapping.

The high pressure Guwahati–Siliguri Pipeline (GSPL) passes through the densely populated Guwahati city in northeast India. This study evaluates response of the GSPL segment within Guwahati city with a focus on the effect of seismic wave induced failure. Seismic sources within a 500 km radius of the Guwahati city are identified and classified into four seismic source regions of (1) Shillong Seismogenic Zone (SSZ), (2) Indo-Burmese Orogenic Front (IBOF), (3) Bengal Deltaic Seismic Block (BDSB), and (4) Eastern Himalayan Seismotectonic Belt (EHSB). The b-values are 1.00 ± 0.03 (SSZ), 1.03 ± 0.02 (IBOF), 0.66 ± 0.06 (BDSB), and 0.93 ± 0.02 (EHSB), indicating elevated seismic activity in BDSB. Deterministic Seismic Hazard Assessment (DSHA) reveal Oldham fault as the source for high level of ground shaking. Peak Ground Accelerations at bedrock level (PGA_b) obtained from DSHA range between 0.219 g to 0.239 g. Probabilistic Seismic Hazard Assessment (PSHA) results reveal that for 2% probability of exceedance in 50 years the PGA_b range between 0.202 g to 0.242 g. At 10% probability of exceedance in 50 years the PGA_b range between 0.126 g to 0.146 g. Hazard curves identify Kopili fault as the contributor for high levels of ground motion at Guwahati city. Further, the study shows that the cumulative strain experienced by the GSPL as a result of tension against axial strain due to seismic wave passage remains below the allowable limit of 3% for worst case scenario, 2% probability of exceedance in 50 years as well as 10% probability of exceedance in 50 years.

On January 7, 2025, an Ms 6.8 earthquake struck Dingri County, Shigatse, Tibet Autonomous Region, causing severe casualties and property losses. This study utilized Sentinel-1 satellite data and Interferometric Synthetic Aperture Radar (InSAR) technology to obtain the co-seismic surface deformation field, invert the fine geometric parameters and slip distribution of the seismogenic fault, and calculate regional co-seismic Coulomb stress changes. Results show that both ascending and descending orbit radar satellites captured the co-seismic deformation, with a field range of 160 km × 100 km and surface rupture of the seismogenic fault. The maximum Line-of-Sight (LOS) deformations were -1.73 m (ascending) and -1.26 m (descending), while azimuth deformations reached -1.11 m and -1.10 m, respectively. Three-dimensional deformation revealed significant subsidence (1.69 m vertical) on the west-side hanging wall and uplift (0.22 m max) on the east-side footwall, indicating normal fault movement along the Dengmocuo Fault. Inversion constrained by InSAR data showed the fault is 32 km long, 14 km wide, with a strike of 187°, dip angle of 56°, and slip angle of -68°, rupturing mainly at 0–16 km depth. The maximum slip was 3.93 m, seismic moment 4.03 × 10¹⁹ N·m, and moment magnitude Mw 7.04. More than 80 aftershocks with M ≥ 3.0 near the Dengmocuo fault were mainly caused by the increase in Coulomb stress caused by the Dingri Mw7.04 earthquake. Considering the influence of historical earthquakes and background tectonic stress, the Coulomb stress change value of the Dingjie County seat will increase by 0.01 MPa after 2047, indicating the possibility of earthquakes occurring. The increase in Coulomb stress change value in the county seat of Gangba is greater than 0.3 MPa, indicating a high possibility of earthquake occurrence.

We used accelerograms from foreshocks recorded by the closest strong-motion stations to the epicentral location of the 2010 El Mayor-Cucapah earthquake (Mw7.2) to estimate S-wave near-source attenuation and to investigate the spatial–temporal evolution of the spectral decay parameter kappa (κ). We found that κ estimated from the foreshocks has significantly higher values compared with those estimated using the mainshock recordings. Since κ is inversely proportional to the quality factor Q and this may vary depending on the state of stress and the presence of fluids, this observation indicates that Q was higher in the epicentral region during the mainshock rupture process, probably due to a higher concentration of stress. We calculated the average regional S-wave attenuation (widetilde{kappa }(r)) before and during the mainshock using a nonparametric approach, and we also found higher attenuation before the occurrence of the main event, suggesting a possible role of fluid flow in the rupture process of the main rupture. Before and during the mainshock (widetilde{kappa }(r)) increased with increasing hypocenter distance, but at short distances (r < 17 km) (widetilde{kappa }(r)) increased faster before the main shock. However, during the main rupture (widetilde{kappa }(r)) increased faster than during the foreshock sequence for r > 17 km, suggesting that the tectonic stress probably decreased beyond that distance. 17 days before the mainshock the near-source attenuation (({kappa }_{s})) was very low in the ruptured area, ({kappa }_{s}=0.0374) s, increasing during the next 30 h to ({kappa }_{s}=) 0.0490 s, then ({kappa }_{s}) started to decrease to the value of ({kappa }_{s}=0.0024) s during the occurrence of the main event. We interpret this decrease in ({kappa }_{s}) as due to increasing Q resulting from an important increase of tectonic stress before the occurrence of the Mw7.2 earthquake. We conclude that κ, in combination with other geophysical parameters, it is useful to understand the preparatory phases of the earthquake rupture process.