Earthquake Research Advances最新文献

Displacement control algorithms commonly used to evaluate axial force-bending moment (PM) diagrams may lead to incorrect interpretations of the strength envelopes for asymmetric sections. This paper aims to offer valuable insights by comparing existing displacement control algorithms with a newly proposed force control algorithm. The main focus is on the PM diagrams of three example sections that exhibit varying degrees of asymmetry. The comparative study indicates that conventional displacement control algorithms inevitably introduce non-zero out-of-plane bending moments. The reported PM diagram in such cases erroneously neglects the out-of-plane moment and fails to represent the strength envelope accurately. This oversight results in significant and unconservative errors when verifying the strength of asymmetric sections.

To enhance the understanding of the geometry and characteristics of seismogenic faults in the Beijing-Tianjin-Hebei region, we relocated 14 805 out of 16 063 earthquakes (113°E−120°E, 36°N–43°N) that occurred between January 2008 and December 2020 using the double-difference tomography method. Based on the spatial variation in seismicity after relocation, the Beijing–Tianjin–Hebei region can be divided into three seismic zones: Xingtai–Wen'an, Zhangbei–Ninghexi, and Tangshan. (1) The Xingtai–Wen'an Seismic Zone has a northeast-southwest strike. The depth profile of earthquakes perpendicular to the strike reveals three northeast-striking, southeast-dipping, high-angle deep faults (>10 ​km depth), including one below the shallow (<10 ​km depth) listric, northwest-dipping Xinghe fault in the Xingtai region. Two additional deep faults in the Wen'an region are suggested to be associated with the 2006 M 5.1 Wen'an Earthquake and the 1967 M 6.3 Dacheng earthquake; (2) The Zhangbei-Ninghexi Seismic Zone is oriented north-northwest. Multiple northeast-striking faults (10–20 ​km depth), inferred from the earthquake-intensive zones, exist beneath the shallow (<10 ​km depth) Xiandian Fault, Xiaotangshan Fault, Huailai-Zhuolu Basin North Fault, Yangyuan Basin Fault and Yanggao Basin North Fault; (3) In the Tangshan Seismic Zone, earthquakes are mainly concentrated near the northeast-striking Tangshan-Guye Fault, Lulong Fault, and northwest-striking Luanxian-Laoting Fault. An inferred north-south-oriented blind fault is present to the north of the Tangshan-Guye Fault. The 1976 M 7.8 Tangshan earthquake occurred at the junction of a shallow northwest-dipping fault and a deep southeast-dipping fault. This study emphasizes that earthquakes in the region are primarily associated with deep blind faults. Some deep blind faults have different geometries compared to shallow faults, suggesting a complex fault system in the region. Overall, this research provides valuable insights into the seismogenic faults in the Beijing–Tianjin–Hebei region. Further studies and monitoring of these faults are essential for earthquake mitigation efforts in this region.

This study analyzed and summarized in detail the spatial and temporal distributions of earthquakes, tidal responses, focal mechanisms, and stress field characteristics for the M 7.3 Haicheng earthquake sequence in February 1975. The foreshocks are related to the main fault and the conjugate faults surrounding the extension step-over in the middle. The initiation timing of the foreshock clusters and the original time of the mainshock were clearly modulated by the Earth's tidal force and coincided with the peak of dilational volumetric tidal strain. As a plausible and testable hypothesis, we proposed a fluid-driven foreshock model, by which all observed seismicity features can be more reasonably interpreted with respect to the results of existing models. Together with some other known examples, the widely existing step-over along strike-slip faults and associated conjugate faults, especially for extensional ones in the presence of deep fluids, favor the occurrence of short-term foreshocks. Although clustered seismicity with characteristics similar to those of the studied case is not a sufficient and necessary condition for large earthquakes to occur under similar tectonic conditions, it undoubtedly has a warning significance for the criticality of the main fault. Subsequent testing would require quantification of true/false positives/negatives.

To enable the experimental assessment of the seismic performance of full-scale nonstructural elements with multiple engineering parameters (EDPs), a three-layer testbed named Nonstructural Element Simulator on Shake Table (NEST) has been developed. The testbed consists of three consecutive floors of steel structure. The bottom two floors provide a space to accommodate a full-scale room. To fully explore the flexibility of NEST, we propose a novel control strategy to generate the required shake table input time histories for the testbed to track the target floor motions of the buildings of interest with high accuracy. The control strategy contains two parts: an inverse dynamic compensation via simulation of feedback control systems (IDCS) algorithm and an offline iteration procedure based on a refined nonlinear numerical model of the testbed. The key aspects of the control strategy were introduced in this paper. Experimental tests were conducted to simulate the seismic responses of a full-scale office room on the 21^st floor of a 42-story high-rise building. The test results show that the proposed control strategy can reproduce the target floor motions of the building of interest with less than 20% errors within the specified frequency range.

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.