Earthquake Science最新文献

The Tian Shan is a vast range that spans several countries in Asia. Understanding its evolutionary history may provide valuable insights into intracontinental orogenic dynamics. In this study, we explored the crustal characteristics of the Tian Shan and their relationships to the tectonic evolution of the region. A new H-stacking method that combines the P receiver function and gravity anomalies was used to estimate the thickness and ratio of P- to S-wave velocities (v_P/v_S) for 91 broadband seismic stations in the central and western Tian Shan. Our results revealed significant lateral variations in crustal thickness and v_P/v_S. A ∼45-km-thick crust and an intermediate-high v_P/v_S (∼1.74–1.84) were found in the Kazakh Shield and Tarim Basin, which we interpreted to indicate a mafic crystalline basement and lower crust. The central Tian Shan varied greatly in crustal thickness (40–64 km) and v_P/v_S ratio (1.65–2.00), which may be due to crustal shortening, mafic underplating, and crustal melting. In contrast, we observed a relatively thin crust (42–50 km) with an intermediate v_P/v_S ratio (∼1.78) in the western Tian Shan. The differences in the crustal structures between the western and central Tian Shan imply that the Talas-Fergana Fault may be trans-lithospheric.

Strong ground motions caused by earthquakes with magnitudes ranging from 3.5 to 6.9 and hypocentral distances of up to 300 km were recorded by local broadband stations and three-component accelerograms within Georgia’s enhanced digital seismic network. Such data mixing is particularly effective in areas where strong ground motion data are lacking. The data were used to produce models based on ground-motion prediction equations (GMPEs), one benefit of which is that they take into consideration information from waveforms across a wide range of frequencies. In this study, models were developed to predict ground motions for peak ground acceleration and 5%-damped pseudo-absolute-acceleration spectra for periods between 0.01 and 10 s. Short-period ground motions decayed faster than long-period motions, though decay was still in the order of approximately 1/r. Faulting mechanisms and local soil conditions greatly influence GMPEs. The spectral acceleration (SA) of thrust faults was higher than that for either strike-slip or normal faults but the influence of strike-slip faulting on SA was slightly greater than that for normal faults. Soft soils also caused significantly more amplification than rocky sites.

We present results of a detailed analysis of data obtained from seismic geodynamic field studies conducted at proposed sites for the development of advanced seismic monitoring stations in the Republic of Armenia. These studies aim to determine the background seismic and geodynamic noise level around such sites. Finally, based on the received data and international standards, nine survey points were classified into respective classes according to their noise level. We also calculated minimum significant earthquake magnitude detectable by the proposed seismic network in different regions of Armenia and mapped it based on recorded regional earthquakes. The resulting map indicates that the proposed seismic monitoring network will provide homogenous initial data for the various seismically active regions of the territory of the Republic of Armenia.

Chao Lake is a Geoheritage site on the active Tan-Lu Fault between the Yangtze craton, the North China craton, and the Dabie orogenic belt in the southeast. This segment of the fault is not well constrained at depth partly due to the overprinting of the fault zone by intrusive materials and its relatively low seismic activity and sparse seismic station coverage. This study took advantage of a dense seismic array deployed around Chao Lake to delineate the P-wave velocity variations in the crust and uppermost mantle using teleseismic earthquake arrival time tomography. The station-pair double-difference with waveform cross-correlation technique was employed. We used a multiscale resolution 3-D initial model derived from the combination of high-resolution 3-D v_S models within the region of interest to account for the lateral heterogeneity in the upper crust. The results revealed that the velocity of the upper crust is segmented with structures trending in the direction of the strike of the fault. Sedimentary basins are delineated on both sides of the fault with slow velocities, while the fault zone is characterized by high velocity in the crust and uppermost mantle. The high-velocity structure in the fault zone shows characteristics of magma intrusion that may be connected to the Mesozoic magmatism in and around the Middle and Lower Yangtze River Metallogenic Belt (MLYMB), implying that the Tan-Lu fault might have formed a channel for magma intrusion. Magmatic material in Chao Lake is likely connected to the partial melting, assimilation, storage, and homogenization of the uppermost mantle and the lower crustal rocks. The intrusions, however, seem to have suffered severe regional extension along the Tan-Lu fault driven by the eastward Paleo-Pacific plate subduction, thereby losing its deep trail due to extensional erosion.

The Menyuan area is an important transportation hub in the Hexi Corridor. The Menyuan M_S6.9 earthquake that occurred on January 8, 2022 had a major impact on the local infrastructure and transportation of this region. Due to the high possibility of similar strong earthquakes occurring in this area in the future, preliminary assessment of the seismic intensity characteristics of destructive earthquakes in this region is essential for effective disaster control. This paper uses the empirical Green′s function (EGF) method as a numerical simulation tool to predict the ground motion intensity of Datong Autonomous County under the action of the scenario earthquake (M_S7.5). Seismic records of aftershocks of the 2016 Menyuan M_S6.4 earthquake were used as Green’s functions for this simulation. The uncertainties associated with various source parameters were considered, and 36 possible earthquake scenarios were simulated to obtain 72 sets of horizontal ground motions in Datong County. The obtained peak ground acceleration (PGA) vs. time histories of the horizontal ground motion were screened using the attenuation relationships provided by the fifth-edition of China's Seismic Ground Motion Parameter Zoning Map and the NGA-West2 dataset. Ultimately, 32 possible acceleration-time histories were selected for further analysis. The screened PGA values ranged from 78.8 to 153 cm/s². The uncertainty associated with the initial rupture point was found to greatly affect the results of the earthquake simulation. The average acceleration spectrum of the selected acceleration-time history exceeded the expected spectrum of a intermediate earthquake, which means that buildings in Datong County might sustain some damage should the scenario earthquake occur. This research can provide reliable ground motion input for urban earthquake damage simulation and seismic design in Datong County. Growing the dataset of small earthquakes recorded in this region will facilitate the large-scale simulation of ground motions under different earthquake scenarios.

The North China Craton (NCC) is one of the oldest cratons on earth. Several important tectonic transformations of Mesozoic-Cenozoic tectonic regime led to the destruction of the North China craton. The knowledge of crustal structure can provide important constraints for the formation and evolution of cratons. New maps of sediment thickness, crustal thickness (H) and v_P/v_S (κ) in the central and western NCC were obtained using sequential H-κ stacking. P-wave receiver functions are calculated using teleseismic waveform data recorded by 405 stations from ChinArray project. Benefiting from the densely distribution of temporary seismic stations, our results reveal details of the crustal structure in the study area. The thickness of sedimentary layer in North China ranges from 0–6.4 km, and the thickest sedimentary layer is in Ordos block and its surroundings (about 2.8–6 km); The thickness of sedimentary layer in the Mongolia fold belt and Yinshan orogenic belt is relatively thin (less than 1 km). The crustal thickness of the study area varies between 27–48 km, of which the crust of the North China Plain is about 30–33 km, the central NCC is about 33–40 km, and the Ordos block is 40–48 km thick. The average v_P/v_S ratios in the study area is mostly between 1.66 and 1.90, and that in the Yanshan-Taihang mountain fold belt is between 1.70 and 1.85, and that in the Ordos block is between 1.65 and 1.90, with an average value of 1.77, indicating the absence of a thick basaltic lower crust. The obvious negative correlation between crustal thickness and average v_P/v_S ratio within Ordos and Central Asia orogenic belt may be related to magmatic underplating during the crustal formation. There is no significant correlation between the crustal thickness and the v_P/v_S ratio in the Lüliang-Taihang mountain fold belt, which may be related to the multiple geological processes such as underplating and crustal extension and thinning in this area. The lack of correlation between crust thickness and topography in the central orogenic belt and the North China Basin indicates the topography of these areas are controlled not only by crustal isostatic adjustment but also by the lithospheric mantle processes.

According to the China Earthquake Networks Center, a strong earthquake of M6.8 occurred in Luding County, Ganzi Tibetan Autonomous Prefecture, Sichuan Province, China (102.08°E, 29.59°N), on September 5, 2022, with a focal depth of 16 km. Rapid determination of the source parameters of the earthquake sequence is vital for post-earthquake rescue, disaster assessment, and scientific research. Near-field seismic observations play a key role in the fast and reliable determination of earthquake source parameters. The numerous broadband seismic stations and strong-motion stations recently deployed by the National Earthquake Intensity Rapid Report and Early Warning project have provided valuable real-time near-field observation data. Using these near-field observations and conventional mid- and far-field seismic waveform records, we obtained the focal mechanism solutions of the mainshock and M ≥ 3.0 aftershocks through the waveform fitting method. We were further able to rapidly invert the rupture process of the mainshock. Based on the evaluation of the focal mechanism solution of the mainshock and the regional tectonic setting, we speculate that the Xianshuihe fault formed the seismogenic structure of the M6.8 strong earthquake. The aftershocks formed three spatially separated clusters with distinctly different focal mechanisms, reflecting the segmented nature of the Xianshuihe fault. As more high-frequency information has been applied in this study, the absolute location of the fault rupture is better constrained by the near-field strong-motion data. The rupture process of the mainshock correlates well with the spatial distribution of aftershocks, i.e., aftershock activities were relatively weak in the maximum slip area, and strong aftershock activities were distributed in the peripheral regions.

The lower Jinsha River basin is located at the junction of Sichuan and Yunnan provinces in Southwest China, a region with intense tectonic movements and frequent moderate to strong seismic activities. Cascade hydropower stations have been constructed along the lower Jinsha River since 2012. However, research on the effect of the impoundment of large-scale cascade reservoirs in a river basin on local seismic activities is currently lacking. Accurately identifying earthquake locations is essential for studying reservoir-induced earthquakes. Analyzing the spatiotemporal migration process of seismic activities based on complete and precise earthquake relocation is fundamental for determining the fluid diffusion coefficient, constructing fault models for reservoir areas, identifying earthquake types, exploring earthquake mechanisms, and evaluating seismic hazards. The seismicity pattern in the Xiangjiaba and Xiluodu reservoir areas, where seismic activities had been weak for a long time, has changed with the successive impoundment of the two reservoirs, showing microseismic events and seismic clusters. We investigated the spatiotemporal characteristics of seismic activities in the Xiangjiaba and Xiluodu reservoir areas using the waveform cross-correlation-based double-difference relocation technique and the b-value analysis method. We discovered that seismic events after the impoundment of these two reservoirs exhibited different characteristics in different regions. The seismic activities at the Xiluodu dam quickly responded to the rising water level, with the seismic intensity decaying rapidly afterward. These events were concentrated in the limestone strata along both sides of the Jinsha River, with a shallow focal depth, generally within 5 km, and a high b-value of approximately 1.2. Such features are close to those of karst-type earthquakes. Microseismic activities frequent occur on the eastern bank of the Yongshan reservoir section downstream of the Xiluodu dam, with two parallel NW-trending earthquake strips visible after precise earthquake relocation. The M_S5.2 earthquake near Wuji town on August 17, 2014, had prominent foreshocks and aftershocks distributed in a clear NW-trending 20-km-long strip, perpendicular to the riverbank. These seismic events had a low b-value of approximately 0.7. The orientation of the node plane revealed by the strike-slip focal mechanism of the mainshock is consistent with that of the strip formed by the foreshock-mainshock-aftershock sequence, indicating the existence of a NW-striking concealed fault. Seismic activities near the Yanjin-Mabian fault upstream of the Xiangjiaba reservoir area since 2013 were concentrated in a NW-trending strip, with several near EW-trending seismic clusters on its western side, and with the largest event having a magnitude of M_L3.7. So far, the impoundment of the Xiangjiaba and Xiluodu reservoirs has not trigg