Earthquake Research Advances最新文献

Quantitative geomorphic analyses are usually powerful in identifying active tectonics across global orogenic belts. Our present study will focus on the Anatolian Plate which hosts a lot of recent catastrophic earthquakes in Türkiye. Six geomorphic indices for 100 sub-basins around Türkiye have been computed including local relief, slope, normalized steepness index (k_Sn)), hypsometric curve and integral (HI), transverse topographic symmetry factor (Tf), and the basin asymmetry factor (Af). The averaged k_Sn and Af values have shown four high-value anomalous zones, suggesting relatively high uplift rates featured by high river incision and regional tilting. The values of 0.35 ​≤ ​HI ​< ​0.6 for basins with S-shaped curves imply intensive tectonic activities along the eastern part of the North Anatolian Fault Zone (NAFZ), the Northeast Anatolian Fault Zone (NEAFZ), the East Anatolian Fault Zone (EAFZ), and the Central Anatolian Fault Zone(CAFZ). All results of the geomorphic indices analysis suggest a relatively high degree of tectonic activity in the following four areas, the Isparta Angle, the Eastern Black Sea Mountains, the South-eastern Anatolia Region, and the Central Anatolian fault zone. We further suggest that the eastern part of the NAFZ, NEAFZ, EAFZ, and CAFZ will be more active in tectonic activities, with a greater potential for strong earthquake occurrence.

Both M_W 7.8 and M_W 7.5 earthquakes occurred in southeastern Türkiye on February 6, 2023, resulting in numerous buildings collapsing and serious casualties. Understanding the distribution of coseismic surface ruptures and secondary disasters surrounding the epicentral area is important for post-earthquake emergency and disaster assessments. High-resolution Maxar and GF-2 satellite data were used after the events to extract the location of the rupture surrounding the first epicentral area. The results show that the length of the interpreted surface rupture zone (part of) is approximately 75 ​km, with a coseismic sinistral dislocation of 2–3 ​m near the epicenter; however, this reduced to zero at the tip of the southwest section of the East Anatolia Fault Zone. Moreover, dense soil liquefaction pits were triggered along the rupture trace. These events are in the western region of the Eurasian Seismic Belt and result from the subduction and collision of the Arabian and African Plates toward the Eurasian Plate. The western region of Chinese mainland and its adjacent areas are in the eastern section of the Eurasian Seismic Belt, where seismic activity is controlled by the collision of the Indian and Eurasian Plates. Both China and Türkiye have independent tectonic histories.

When evaluating an area's seismic risk or resilience, it is necessary to use the spatial correlation to analyze the ground motion parameters of multiple sites together in an earthquake. These two large earthquakes in Türkiye provided the possibility for spatial correlation analysis of ground motion intensity measurements in this area. Based on the strong motion records provided by The Disaster and Emergency Management Authority of Türkiye (AFAD), this study uses the local ground motion prediction equation ​in Türkiye to give spatial correlation analysis of Intensity Measurements. This study gives an exponential model based on a semivariogram and compares it with the correlation model obtained from previous studies.

We collected high-quality teleseismic events recorded by 12 broadband seismographs deployed in the Anyuan Coal Mine and its adjacent areas in Pingxiang City, Jiangxi Province for nearly two years. The H-κ-c stacking method was employed to obtain the crustal thickness and Poisson's ratio distribution, then the characteristics of crustal structure below the stations were obtained by using the time-domain linear inversion method. The crustal thickness in the Anyuan Coal Mine and its adjacent areas ranges from approximately 32 $\sim$ 35 ​km, with an average thickness of 33 ​km, which is consistent with the crustal thickness results in South China from previous studies using the receiver function method. The average Poisson's ratio of the crustal bulk composition in the study area varies between 0.22 and 0.25, which is lower than the global value with a 0.27 average, indicating a predominantly intermediate-acidic or felsic crustal composition. There is a weak negative correlation between Poisson's ratio and crustal thickness estimates in the Anyuan Coal Mine and its adjacent areas, suggesting that the absence of mafic-ultramafic materials in the lower crust is associated with the process of crustal delamination. The velocity inversion results indicate that the crustal structure including three velocity discontinuity interfaces, with the first at a depth of approximately 1.5 ​km, the second at about 10 $\sim$ 15 ​km, and the third being the Moho. The study also indicates that the results obtained by the H-κ-c stacking method are significantly better than those obtained by the H-κ method, effectively reducing the standard deviation and dispersion of crustal thickness and v_P/v_S ratio.

Monitoring seismicity in real time provides significant benefits for timely earthquake warning and analyses. In this study, we propose an automatic workflow based on machine learning (ML) to monitor seismicity in the southern Sichuan Basin of China. This workflow includes coherent event detection, phase picking, and earthquake location using three-component data from a seismic network. By combining PhaseNet, we develop an ML-based earthquake location model called PhaseLoc, to conduct real-time monitoring of the local seismicity. The approach allows us to use synthetic samples covering the entire study area to train PhaseLoc, addressing the problems of insufficient data samples, imbalanced data distribution, and unreliable labels when training with observed data. We apply the trained model to observed data recorded in the southern Sichuan Basin, China, between September 2018 and March 2019. The results show that the average differences in latitude, longitude, and depth are 5.7 ​km, 6.1 ​km, and 2 ​km, respectively, compared to the reference catalog. PhaseLoc combines all available phase information to make fast and reliable predictions, even if only a few phases are detected and picked. The proposed workflow may help real-time seismic monitoring in other regions as well.

Large earthquakes can cause both casualties and economic losses, but they also provide invaluable opportunities for earthquake scientific research. Geofluids, due to their wide distribution, sensitive response to underground conditions, and ease of observation, are widely applied in field investigations after earthquakes. Analyzing the origin of fluids, energy transfer processes, temperature/pressure conditions, and the spatial-temporal evolution of geofluids can provide valuable information concerning the mechanism of earthquake precursor anomalies, short-term prediction methods, identification of the seismogenic faults, determination of earthquake risk, and the environmental impact of post-earthquake fluids. This article details post-earthquake scientific expeditions and research on fluid geochemistry in China and abroad, aimed at providing ideas and guidance for future scientific expedition work and geochemistry-related earthquake studies.

Decoding the variation laws of the deformation field before strong earthquakes has long been recognized as an essential issue in earthquake prediction research. In this paper, the temporal and spatial distribution characteristics of deformation anomalies in the northeastern margin of the Qinghai-Tibetan Plateau before and after the Menyuan M_S 6.9 earthquake were studied by using the Fisher statistical test method. By analyzing the characteristics of these anomalies, we found that: 1) The deformation anomalies are mainly distributed in the marginal front area of the Qinghai-Tibetan Plateau, where short-term deformation anomalies are prone to occur due to a high gradient of gravity; 2) The deformation anomalies along the northeastern margin of the Qinghai-Tibetan Plateau are characterized by spatial propagation, and the migration rate is about 2.4 ​km/d. The propagation pattern is counterclockwise, consistent with the migration direction of M_S ​≥ ​6.0 earthquakes; 3) The time and location of the Menyuan earthquake are related to the group migration of earthquakes with M_S ​≥ ​6.0. Finally, based on the results of gravity field variation and the theory of crust stress wave, the law of deformation anomaly distribution was discussed. We suggest that both the deformation propagation along the northeastern margin of the Qinghai-Tibetan Plateau and the earthquake migration are possibly associated with the variation of the stress field caused by subsurface mass flow.

The central-southern part of the eastern border of the Sichuan-Yunnan rhombic block provides the research strategy of ‘trade space for time’ with an interesting fault system, where the segments have similar focal mechanisms and cover almost continuous spectra of elapse rates. We experiment to study the seismological characteristics of different segments with different elapse rates. We employed the de-clustered earthquake catalog for the calculation of b values for each segment. The analysis revealed that different segments have similar b values, which implies that, although different segments have different periods of earthquake recurrence, the 'natural time' for the whole fault system elapses with a homogeneous pace. We extended the earthquake potential score (EPS) for nowcasting earthquakes to a quasi-EPS (qEPS). It is found that qEPS increases with the increase of elapse rates, albeit for those fault segments whose elapse rates have exceeded 1, qEPS may better reflect the seismic hazard.

After the occurrence of destructively strong earthquakes, rapid acquisition of the source rupture process can provide important reference information for post-earthquake disaster relief and aftershock trend determination. An M 6.9 earthquake occurred in Menyuan County, Qinghai Province on January 8, 2022. The epicenter is located in the seismic gap in the middle section of the Haiyuan fault belt. Such a typical strong earthquake was taken as an example to investigate the rupture process of strong earthquakes. Three days after the earthquake, the InSAR (Interferometric Synthetic Aperture Radar) coseismic deformation field was obtained by Sentinel radar, indicating that the surface ruptured obviously. The southern block of the earthquake faces towards the satellite about 95 ​cm along the LOS (line of sight) direction, and the northern block is away from the satellite by ​∼ ​74 ​cm, consistent with the characteristic of left-lateral strike-slip motion. In this study, InSAR coseismic deformation data and far-field waveform data were used to jointly invert the earthquake rupture process, and a four-segment finite fault model was constructed by referring to the surface deformation. The inversion results show that the focal depth of the Menyuan earthquake is about 7 ​km, and the strike of the seismogenic fault is 89.0°, 104.0°, 119.0° and 131.0° from west to east, respectively. It is a high-dip left-lateral strike-slip earthquake event lasting about 14 ​s. The rupture propagation mode is a bilateral extension. The maximum slip along the fault is about 380 ​cm, and the seismic moment magnitude is 6.7. The surface rupture length is about 24 ​km, which is consistent with that measured in the field survey. The detailed seismic source model can provide basic data for the aftershock trend determination and seismic risk analysis of the adjacent active faults.