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Articles in press have been peer-reviewed and accepted, which are not yet assigned to volumes /issues, but are citable by Digital Object Identifier (DOI).
Crustal structure beneath North China determined using the receiver function method
Xin Gao, YongHua Li, XiaoYu Yang, ZhiYuan Ren
Abstract Full HTML(0) PDF[9329KB](0)
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The North China Craton (NCC) is one of the oldest cratons on Earth. Several significant tectonic transformations during the Mesozoic-Cenozoic tectonic regime have led to the destruction of the NCC. Knowledge of its crustal structure could provide important constraints to elucidate the formation and evolution of a craton. Accordingly, we investigated the crustal structure of the central and western regions of the NCC using sequential H-k stacking. The P-wave receiver functions were calculated using teleseismic waveform data recorded by 405 densely distributed temporary seismic stations in the ChinArray project. Subsequently, we constructed new maps of the sediment and crustal thicknesses, as well as the vP/vS ratio in the study area. The sedimentary layers in North China are 0–6.4 km thick; the thickest sedimentary layer is located in the Ordos block and its surroundings (approximately 2.8–6 km). The sedimentary layers in the north of the Inner Mongolia fold belt and northeast of the Yinshan orogenic belt are relatively thin (not exceeding 1 km). The crustal thickness of the study area ranges between 27 and 48 km, with that of the North China Plain, central Taihang-Lüliang area, and Ordos block being approximately 30–33, 33–40, and 40–47 km, respectively. The average vP/vS ratio in the study area is between 1.66 and 1.88, 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 1.76, indicating the absence of a thick basaltic lower crust. The substantial negative correlation between crustal thickness and average vP/vS ratio within the Ordos block and Central Asia Orogenic Belt could be related to magmatic underplating during crustal formation. No significant correlation was found between crustal thickness and vP/vS in the Lüliang–Taihang Mountain fold belt, probably owing to multiple geological processes, such as underplating and crustal extension and thinning, occurring in this area. The lack of correlation between crustal thickness and topography in the central orogenic belt and the North China Basin indicates that the topography of these areas is controlled not only by crustal isostatic adjustment, but also by lithospheric mantle processes.
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Preface to the special issue on ground motion input at dam sites and reservoir earthquakes
Ruifang Yu, Xiao Hu, Ruizhi Wen
Abstract Full HTML(3) PDF[3296KB](0)
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Seismic hazard analysis for engineering sites based on the stochastic finite-fault method
Ruifang Yu, Yisheng Song, Xiangyun Guo, Qianli Yang, Xinjuan He, Yanxiang Yu
 doi: 10.1016/j.eqs.2022.05.007
Abstract Full HTML(141) PDF[5771KB](23)
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Seismic hazard analyses are mainly performed using either deterministic or probabilistic methods. However, there are still some defects in these statistical model-based approaches for regional seismic risk assessment affected by the near-field of large earthquakes. Therefore, we established a deterministic seismic hazard analysis method that can characterize the entire process of ground motion propagation based on stochastic finite-fault simulation, and we chose the site of the Xiluodu dam to demonstrate the method. This method can characterize earthquake source properties more realistically than other methods and consider factors such as the path and site attenuation of seismic waves. It also has high computational efficiency and is convenient for engineering applications. We first analyzed the complexity of seismogenic structures in the Xiluodu dam site area, and then an evaluation system for ground motion parameters that considers various uncertainties is constructed based on a stochastic finite-fault simulation. Finally, we assessed the seismic hazard of the dam site area comprehensively. The proposed method was able to take into account the complexity of the seismogenic structures affecting the dam site and provide multi-level parameter evaluation results corresponding to different risk levels. These results can be used to construct a dam safety assessment system of an earthquake in advance that provides technical support for rapidly and accurately assessing the post-earthquake damage state of a dam, thus determining the influence of an earthquake on dam safety and mitigating the risk of potential secondary disasters.
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Influence of seismic wave type and incident direction on the dynamic response of tall concrete-faced rockfill dams
Chen-guang Zhou, De-gao Zou, Xiang Yu
Abstract Full HTML(6) PDF[6451KB](1)
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Owing to the stochastic behavior of earthquakes and complex crustal structure, wave type and incident direction are uncertain when seismic waves arrive at a structure. In addition, because of the different types of the structures and terrains, the traveling wave effects have different influences on the dynamic response of the structures. For the tall concrete-faced rockfill dam (CFRD), it is not only built in the complex terrain such as river valley, but also its height has reached 300 m level, which puts forward higher requirements for the seismic safety of the anti-seepage system mainly comprising concrete face slabs, especially the accurate location of the weak area in seism. Considering the limitations of the traditional uniform vibration analysis method, we implemented an efficient dynamic interaction analysis between a tall CFRD and its foundation using a non-uniform wave input method with a viscous-spring artificial boundary and equivalent nodal loads. This method was then applied to investigate the dynamic stress distribution on the concrete face slabs for different seismic wave types and incident directions. The results indicate that dam-foundation interactions behave differently at different wave incident angles, and that the traveling wave effect becomes more evident in valley topography. Seismic wave type and incident direction dramatically influenced stress in the face slab, and the extreme stress values and distribution law will vary under oblique wave incidence. The influence of the incident direction on slab stress was particularly apparent when SH-waves arrived from the left bank. Specifically, the extreme stress values in the face slab increased with an increasing incident angle. Interestingly, the locations of the extreme stress values changed mainly along the axis of the dam, and did not exhibit large changes in height. The seismic safety of CFRDs is therefore lower at higher incident angles from an anti-seepage perspective. Therefore, it is necessary to consider both the seismic wave type and incident direction during seismic capacity evaluations of tall CFRDs.
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P-wave velocity structure in the crust and the uppermost mantle of Chao Lake region of the Tan-Lu Fault inferred from teleseismic arrival time tomography
Bem Shadrach Terhemba, Song Luo, Lei Gao, Haijiang Zhang, Junlun Li
Abstract Full HTML(4) PDF[9848KB](1)
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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 vS 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.
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Rupture process and aftershock mechanisms of the 2022 Luding M6.8 earthquake in Sichuan, China
Zhigao Yang, Danqing Dai, Yong Zhang, Xuemei Zhang, Jie Liu
 doi: 10.1016/j.eqs.2022.09.001
Abstract Full HTML(23) PDF[3199KB](4)
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On September 5, 2022, a strong earthquake of M6.8 occurred in Luding County (102.08°E, 29.59°N), Sichuan, China, with a focal depth of 16km, from the rapid earthquake information released by China Earthquake Networks Center:It is of great importance to quickly determine the source parameters of an earthquake sequence for earthquake rescue, disaster assessment and scientific research. Near-field seismic observations play a key role in the fast and reliable determination of source parameters. A large number of broadband and strong motion stations newly built by the National Intensity Rapid Report and Early Warning Project of China Earthquake Administration provide valuable near-field real-time observation data. Based on these near-field observations and traditional mid- and far-field seismic waveform data, we can use the waveform fitting method to determine the focal mechanism solutions of the mainshock and M≥3.0 aftershocks, and to quickly invert the rupture process of the mainshock. Combined with the focal mechanism solution of the main shock and the regional tectonic background, it is inferred that the M6.8 earthquake is associated with the Xianshuihe fault. The focal mechanism solutions of aftershocks show that there are obvious differences in focal mechanisms of three earthquake swarms of aftershocks, reflecting the segmentation characteristics of the Xianshuihe fault zone. The near-field strong motion data have better constraints on the absolute location of the rupture due to the use of more high-frequency information. The rupture process of main shock has a good correspondence with the spatial distribution of aftershocks, i.e., areas with large rupture slip correspond to weak aftershocks, and edges of large slips have strong aftershocks.
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Influence of the quality factor on simulated seismic waves: A case study of the 1994 Northridge earthquake
Qingpei Zeng, Xiangchao Wang, Jinting Wang
Abstract Full HTML(13) PDF[7415KB](37)
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In numerical simulations of ground motion, the constant quality factor Q of a viscoelastic medium can be determined using the time-domain constitutive approximation method of the generalized standard linear solid (GSLS) model. This study introduces a numerical seismic wavefield simulation method which combines the spectral element method with the constant-Q model. The method is used to simulate the seismic wavefield of the 1994 Northridge earthquake. The optimal attenuation coefficient for the simulated seismic waves in this study area is determined empirically based on a quantitative analysis of the deviation curve. Further, the effect of the quality factor on the simulated wavefield are analyzed according to the site characteristics of each seismic station. The quality factor shows a variable effect on the different frequency components of the simulated wavefield. The effect of the quality factor also varies with the characteristic parameters of each seismic station site, such as site velocity structure, fault distance, and azimuth angle.
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Influence of regional background stress fields on the spontaneous rupture of the major faults around Xiluodu Dam, China
Li Liao, Pingen Li, Jiansi Yang, Jianzhou Feng
Abstract Full HTML(10) PDF[8383KB](2)
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Simulations of the spontaneous rupture of potential earthquakes in the vicinity of reservoir dams can provide accurate parameters for seismic resilience assessment, which is essential for improving the seismic performance of reservoir dams. In simulations of potential spontaneous ruptures, fault geometry, regional stress fields, constitutive parameters of the fault friction law, and many other factors control the slip rate, morphology, and dislocation of the rupture, thereby affecting the simulated ground motion parameters. The focus of this study was to elucidate the effects of the background stress field on the nucleation and propagation of spontaneous ruptures based on the factors influencing potential M > 7 earthquake events on the Leibo Middle Fault (LBMF) and the Mabian-Yanjing Fault (MB-YJF) in the Xiluodu Dam (XLD) region. Our simulation results show that the magnitude of the regional background stress field plays a decisive role in whether a destructive earthquake exceeding the critical magnitude will occur. We found that the direction and magnitude of the regional stress significantly affect the range of rupture propagation on the fault plane, and fault geometry affects the spatial distribution of the rupture range. Under the same regional stress field magnitude and orientation, a more destructive, high-magnitude earthquake is more likely to occur on the LBMF than on the MB-YJF.
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Seismic analysis of the Xiluodu Reservoir area and insights into the geometry of seismogenic faults
Hongfu Lei, Qincai Wang, Cuiping Zhao, Ce Zhao, Jinchuan Zhang, Jun Li
Abstract Full HTML(6) PDF[11691KB](1)
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The Xiluodu (XLD) Reservoir is the second largest reservoir in China and the largest in the Jinsha River Basin. The occurrence of two M > 5 earthquakes after reservoir impoundment has aroused great interest among seismologists and plant operators. We comprehensively analyzed the seismicity of the XLD Reservoir area using precise earthquake relocation results and focal mechanism solutions and found that the seismicity of this area was weak before impoundment. Following impoundment, earthquake activity increased significantly. The occurrence of M ≥ 3.5 earthquakes within five years of impoundment also appear to be closely related to rapid rises and falls in water level, though this correlation weakened after five years because earthquake activity was far from the reservoir area. Earthquakes in the XLD Reservoir area are clustered; near the dam (Area A), small faults are intermittently distributed along the river, while Area B is composed of multiple NW-trending left-lateral strike–slip faults and a thrust fault and Area C is composed of a NW-trending left-lateral strike–slip main fault and a nearly EW-trending right-lateral strike–slip minor fault. The geometries of the deep and the shallow parts of the NW-trending fault differ. Under the action of the NW-trending background stress field, a series of NW-trending left-lateral strike–slip faults and NE-trending thrust faults in critical stress states were dislocated due to the stress caused by reservoir impoundment. The two largest earthquakes in the XLD Reservoir area were tectonic earthquakes that were directly triggered by impoundment.
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Seismic activities before and after the impoundment of the Xiangjiaba and Xiluodu reservoirs in the lower Jinsha River
Ce Zhao, Cuiping Zhao, Hongfu Lei, Mengdi Yao
Abstract Full HTML(11) PDF[3391KB](5)
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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 MS5.2 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 ML3.7. So far, the impoundment of the Xiangjiaba and Xiluodu reservoirs has not triggered seismic activities on the large Jinyang-Ebian and Yanjin-Mabian faults nearby.
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Ground-Motion Prediction Equations Based on Shallow Crustal Earthquakes in Georgia and the Surrounding Caucasus
Jorjiashvili Nato, Shengelia Ia, Godoladze Tea, Gunia Irakli, Akubardia Dimitri
Abstract Full HTML(9) PDF[4895KB](1)
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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 s 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.
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Prediction and verification of earthquakes induced by the Xiluodu hydropower station reservoir
Tinggai CHANG, Baohua LI, Xinxiang ZENG
Abstract Full HTML(5) PDF[9714KB](0)
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Research has been conducted on reservoir-induced earthquakes in China since the Xinfengjiang reservoir-induced earthquakes in the 1960 s. Regulations now require the risk of reservoir-induced earthquakes to be evaluated in the pre-research stage of all hydropower projects. Although nearly 40 cases of reservoir-induced earthquakes have been reported in China, analyses comparing the changes in seismic activity following reservoir impoundment with predictions are rare. In this study, we compared seismic activities observed in the reservoir area before and after the impoundment of the Xiluodu hydropower station in terms of the spatial distribution, frequency, and focal depths of the earthquakes, and clarified the correlation between their frequency/timing and reservoir level after impoundment. We then concluded that the seismic events in the head region were karst-type earthquakes, while those in the second segment of the reservoir were tectonic earthquakes. The spatial distribution of the earthquake epicenters and the seismic intensities validated some of the results for the reservoir-induced seismic risk assessment for the Xiluodu hydropower station, indicating that the proposed earthquake triggers and predictive models are reasonable. This study can provide a valuable reference for investigating the mechanism (s) of reservoir-induced earthquakes, revising reservoir-induced earthquake hazard assessment codes, and predicting the hazard zones of reservoir-induced seismicity under similar conditions.
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Overview of the seismic input at dam sites in China
Houqun Chen
 doi: 10.1016/j.eqs.2022.05.006
Abstract Full HTML(211) PDF[4567KB](18)
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The current Chinese national standard, the Standard for Seismic Design of Hydraulic Structures (GB51247), released in 2018, is strictly based on China’s national conditions and dam engineering features. A comprehensive and systematic overview of the basis of the seismic fortification requirements, the framework of the fortification criteria, and the mechanisms of seismic input related to the seismic design of dams are presented herein. We first analyzed and clarified several conceptual aspects in traditional seismic design of dams. Then, for the seismic input at the dam site described in the first national standard for hydraulic structures, we expounded innovative concepts, ideas, and methods to make relevant provisions more realistic and practical and discussed whether reservoir earthquakes must be included in the seismic fortification framework of dams. This study seeks to incorporate seismic input at the dam site into traditional seismic design practice to promote its improvement from the quasi-static method to the dynamic method and from the closed vibration system to an open wave propagation system, to ensure that the seismic design of dams becomes more reasonable, reliable, scientific, and economic.
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Simulation of strong earthquake characteristics of a scenario earthquake (MS7.5) based on the enlightenment of 2022 MS6.9 earthquake in Menyuan
Zhiwei Ji, Zongchao Li, Mengtan Gao, Jize Sun, Xiangyun Guo
Abstract Full HTML(62) PDF[6181KB](19)
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The Menyuan area is an important transportation hub in the Hexi Corridor. The Menyuan MS6.9 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 (MS7.5). Seismic records of aftershocks of the 2016 Menyuan MS6.4 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.
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DiTing: A large-scale Chinese seismic benchmark dataset for artificial intelligence in seismology
Ming Zhao, Zhuowei Xiao, Shi Chen, Lihua Fang
Abstract Full HTML(305) PDF[4716KB](100)
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In recent years, artificial intelligence technology has exhibited great potential in seismic signal recognition, setting off a new wave of research. Vast amounts of high-quality labeled data are required to develop and apply artificial intelligence in seismology research. In this study, based on the 2013–2020 seismic cataloging reports of the China Earthquake Networks Center, we constructed an artificial intelligence seismological training dataset (“DiTing”) with the largest known total time length. Data were recorded using broadband and short-period seismometers. The obtained dataset included 2,734,748 three-component waveform traces from 787,010 regional seismic events, the corresponding P- and S-phase arrival time labels, and 641,025 P-wave first-motion polarity labels. All waveforms were sampled at 50 Hz and cut to a time length of 180 s starting from a random number of seconds before the occurrence of an earthquake. Each three-component waveform contained a considerable amount of descriptive information, such as the epicentral distance, back azimuth, and signal-to-noise ratios. The magnitudes of seismic events, epicentral distance, signal-to-noise ratio of P-wave data, and signal-to-noise ratio of S-wave data ranged from 0 to 7.7, 0 to 330 km, –0.05 to 5.31 dB, and –0.05 to 4.73 dB, respectively. The dataset compiled in this study can serve as a high-quality benchmark for machine learning model development and data-driven seismological research on earthquake detection, seismic phase picking, first-motion polarity determination, earthquake magnitude prediction, early warning systems, and strong ground-motion prediction. Such research will further promote the development and application of artificial intelligence in seismology.
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Article
Using the match-and-locate method to characterize foreshocks of the July 2019 MW6.4 Ridgecrest, California earthquake
Min Liu, Miao Zhang, Hongyi Li
2022, 35(4): 213-242.   doi: 10.1016/j.eqs.2022.08.005
Abstract Full HTML(279) PDF[45619KB](77)
The July 2019 MW6.4 Ridgecrest, California earthquake and its distinct foreshocks were well recorded by local and regional stations, providing a great opportunity to characterize its foreshocks and investigate the nucleation mechanisms of the mainshock. In this study, we utilized the match-and-locate (M&L) method to build a high-precision foreshock catalog for this MW6.4 earthquake. Compared with the sequential location methods (matched-filter + cross-correlation-based hypoDD), our new catalog contains more events with higher location accuracy. The MW6.4 mainshock was preceded by 40 foreshocks within ~2 h (on July 4, 2019 from 15:35:29 to 17:32:52, UTC). Their spatiotemporal distribution revealed a complex seismogenic structure consisting of multiple fault strands, which were connected as a throughgoing fault by later foreshocks and eventually accommodated the 2019 MW6.4 mainshock. To better understand the nucleation mechanism, we determined the rupture dimension of the largest ML4.0 foreshock by calculating its initial rupture and centroid points using the M&L method. By estimating Coulomb stress change we suggested that the majority of foreshocks following the ML4.0 event and MW6.4 mainshock occurred within regions of increasing Coulomb stress, indicating that they were triggered by stress transfer. The nucleation process before the ML4.0 event remains unclear due to the insufficient sampling rate of waveforms and small magnitude of events. Thus, our study demonstrates that the M&L method has superior detection and location ability, showing potential for studies that require high-precision location (e.g., earthquake nucleation).
Eastward subduction of the Indian plate beneath the Indo-Myanmese arc revealed by teleseismic P-wave tomography
Yu Gao, Jiansi Yang, Yu Zheng
2022, 35(4): 243-262.   doi: 10.1016/j.eqs.2022.08.002
Abstract Full HTML(100) PDF[8325KB](70)
The deep structure of the eastward-subducting Indian plate can provide new information on the dynamics of the India-Eurasia collision. We collected and processed waveform data from temporary seismic arrays (networks) on the eastern Tibetan Plateau, seismic arrays in Northeast India and Myanmar, and permanent stations of the China Digital Seismic Network in Tibet, Gansu, Qinghai, Yunnan, and Sichuan. We combined these data with phase reports from observation stations of the International Seismological Center on the Indian plate and selected 124,808 high-quality P-wave relative travel-time residuals. Next, we used these data to invert the 3-D P-wave velocity structure of the upper mantle to a depth of 800 km beneath the eastern segment of the arcuate Himalayan orogen, at the southeastern margin of the Tibetan Plateau. The results reveal a high-angle, easterly dipping subducting plate extending more than 200 km beneath the Indo-Myanmese arc. The plate breaks off at roughly 96°E; its fragments have passed through the 410-km discontinuity (D410) into the mantle transition zone (MTZ). The MTZ beneath the Tengchong volcanic area contains a high-velocity anomaly, which does not exceed the Red River fault to the east. No other large-scale continuous subducted plates were observed in the MTZ. However, a horizontally spreading high-velocity anomaly was identified on the D410 in some regions. The anomaly may represent the negatively buoyant 90°E Ridge plate or a thickened and delaminated lithospheric block experiencing collision and compression at the southeastern margin of the Tibetan Plateau. The Tengchong volcano may originate from the mantle upwelling through the slab window formed by the break-off of the subducting Indian continental plate and oceanic plate in the upper mantle. Low-velocity upper mantle materials on the west side of the Indo-Myanmese arc may have supplemented materials to the Tengchong volcano.
Determination and application of path duration of seismic ground motions based on the K-NET data in Sagami Bay, Japan
Shiyang Chen, Xiaojun Li, Lei Fu, Su Chen
2022, 35(4): 263-279.   doi: 10.1016/j.eqs.2022.08.003
Abstract Full HTML(48) PDF[10020KB](9)
Duration models are one of the important parameters in ground-motion simulations. This model varies in different study areas, and plays a critical role in nonlinear structural response analysis. Currently, available empirical models are being globally used in ground-motion simulations, with limited research focusing on path duration in specific regions. In this study, we collected 6,486 sets of three-component strong-motion records from 29 K-NET stations in the Sagami Bay, Japan, and its surrounding areas between January 2000 to October 2018. We extracted the effective duration of 386 pieces of ground-motion records by manually picking up the S-wave arrival time and calculating the significant duration. We then obtained the path duration model of the study area based on the empirical equation of dynamic corner frequency and source duration of Boore (2009). Compared with the results of the available empirical models, the Fourier spectrum of the simulated ground motion from our effective duration model showed higher accuracy in the long-term range, with less fitting residuals. This path duration model was then applied to simulate two earthquakes of MW5.4 and MW6.2, respectively, in the region using the stochastic finite-fault method with a set of reliable source, path, and site parameters determined for the study area. The simulation results of most stations fit well with observation records in the 0–30 Hz frequency band. For the MW5.4 earthquake, the simulated ground motions at KNG005/KNG010/SZO008 stations were relatively weak in the mid to high frequency band (1–30 Hz) because the quality factor and geometric diffusion model used in the simulation were the averages of the entire Sagami Bay region, causing a bias in the results of a few stations owing to local crustal velocity anomalies and topographic effects. For the MW6.2 earthquake, the simulated ground motions were relatively weak at all SZO and TKY stations, mainly because of the close distance from these stations to the epicenter and the complex seismic-wave propagation paths. The analysis suggests that the differences between the simulation results of the two earthquakes were mainly related to complex geological conditions and seismic-wave propagation paths.
Comparison of DSHA-based response spectrum with design response spectrum of building code of Pakistan (BCP-SP-2007) for a site in Muzaffargarh area, Pakistan
Naseer Ahmed, Shahid Ghazi
2022, 35(4): 280-292.   doi: 10.1016/j.eqs.2022.08.004
Abstract Full HTML(71) PDF[3373KB](17)
The building code of any country is considered to be a basic technical guidance document for the seismic design of structures. However, building codes are typically developed for the whole country, without considering site specific models that incorporate detailed site-specific data. Therefore, the adequacy of the design spectrum for building codes may sometimes be questionable. To study the sufficiency of the building codes of Pakistan (BCP-SP-2007), a deterministic seismic hazard analysis (DSHA) based spectrum was developed for a site in the Muzaffargarh area, Pakistan, using an updated earthquake catalogue, seismic source model, and a next generation attenuation model (NGA-WEST-2). Further, an International Building Code (IBC-2000) spectrum was developed for the study area to compare the results. The DSHA-based response spectrum resulted in a peak ground acceleration (PGA) value of 0.21 g for the Chaudwan fault. The evaluation of BCP-SP-2007 and IBC-2000 spectra provided a critical assessment for analyzing the associated margins. A comparison with the DSHA-based response spectrum showed that the BCP-SP-2007 design spectrum mostly overlapped with the DSHA spectrum unlike IBC-2000. However, special attention is needed for designing buildings in the study area when considering earthquake periods longer than 1 s, and the BCP-SP-2007 spectrum can be enhanced when considering a period range of 0.12–0.64 s. Finally, BCP-SP-2007 is based on a probabilistic approach and its comparison with deterministic results showed the significance of both methods in terms of design.
Seismogenic environment and mechanism of the Yangbi MS6.4 earthquake in Yunnan, China
Mengqiao Duan, Kezhen Zuo, Cuiping Zhao, Lianqing Zhou
2022, 35(4): 297-310.   doi: 10.1016/j.eqs.2022.08.001
Abstract Full HTML(46) PDF[10196KB](7)
The Yangbi MS6.4 earthquake occurred on May 21, 2021 in western Yunnan, China, where moderate earthquakes strike frequently. It exhibited a typical “foreshock-mainshock-aftershock” sequence and did not occur on a pre-existing active fault. The seismogenic environment and mechanism of this earthquake have aroused considerable research attention. In this study, we obtain the three-dimensional vP, vS and vP/vS images using the vP/vS consistency-constrained double-difference tomography method, which improves the accuracy of vP/vS models. We focus on characteristics of vP/vS images in areas with a lateral resolution of 0.1°, and reveal the seismogenic environment of the Yangbi MS6.4 earthquake. The conclusions are as follows: (1) Low velocity and high-vP/vS anomalies are revealed at different depths around the northern segment of the Red River fault. vS and vP/vS images along the Weixi-Qiaohou-Weishan fault and the buried faults on its west show obviously segmented feature. (2) The source region of the Yangbi MS6.4 earthquake is located in a low-vP/vS zone implying high medium strength. High-vP/vS anomalies in its NW direction indicate cracks development and the existence of fluids or partial melts, which are unfavorable for stress accumulation and triggering large earthquakes. Such conditions have also prevented the earthquake sequence from extending northwestward. (3) With the southeastward extrusion of materials from the Tibetan Plateau, fluid migration was blocked by the low-vP/vS body in the source region. The high-vP/vS anomaly beneath the source region may implies that the fluids or partial melts in the middle and lower crust gradually weakened medium strength at the bottom of the seismogenic layer, and preparing the largest foreshock in the transition zone of high to low vP/vS. Meanwhile, tectonic stress incessantly accumulated in the brittle upper crust, eventually led to the MS6.4 earthquake occurrence.
Opinion
Evaluation of numerical earthquake forecasting models
Zhongliang Wu
2022, 35(4): 293-296.   doi: 10.1016/j.eqs.2022.08.006
Abstract Full HTML(70) PDF[1603KB](10)
Evaluation of numerical earthquake forecasting models needs to consider two issues of equal importance: the application scenario of the simulation, and the complexity of the model. Criterion of the evaluation-based model selection faces some interesting problems in need of discussion.
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