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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).
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
Abstract Full HTML(3) PDF[5101KB](0)
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 regional 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 and IBC 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 using BCP-SP 2007, and the BCP-SP 2007 spectrum should be enhanced when considering a period 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.
Evaluation of numerical earthquake forecasting models
Zhongliang Wu
Abstract Full HTML(4) PDF[3335KB](0)
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.
DiTing: A large-scale Chinese seismic benchmark dataset for artificial intelligence in seismology
Ming Zhao, Zhuowei Xiao, Shi Chen, Lihua Fang
Abstract Full HTML(203) PDF[4716KB](64)
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.
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, Chen Su
Abstract Full HTML(7) PDF[11932KB](2)
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 the MW5.4 and MW6.2 earthquakes 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.
Eastward subduction of the Indian plate beneath the Indo-Burmese arc revealed by teleseismic P-wave tomography
Yu Gao, Jiansi Yang, Yu Zheng
Abstract Full HTML(17) PDF[10207KB](43)
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.
Overview of the seismic input at dam sites in China
Houqun Chen
 doi: 10.1016/j.eqs.2022.05.006
Abstract Full HTML(162) PDF[4741KB](13)
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.
Using the match-and-locate method to characterize foreshocks of the July 2019 Mw 6.4 Ridgecrest, California earthquake
Min Liu, Miao Zhang, Hongyi Li
Abstract Full HTML(37) PDF[8433KB](15)
The July 2019 Mw 6.4 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 Mw 6.4 earthquake. Compared with the sequential location methods (matched-filter + cross-correlation-based hypoDD), our new catalog contains more events with higher location accuracy. The Mw 6.4 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 Mw 6.4 mainshock. To better understand the nucleation mechanism, we determined the rupture dimension of the largest ML 4.0 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 ML 4.0 event and Mw 6.4 mainshock occurred within regions of increasing Coulomb stress, indicating that they were triggered by stress transfer. The nucleation process before the ML 4.0 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).
Seismogenic environment and mechanism of the Yangbi MS6.4 earthquake in Yunnan, China
Mengqiao Duan, Kezhen Zuo, Cuiping Zhao, Lianqing Zhou
Abstract Full HTML(7) PDF[12110KB](2)
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.
Influence of the quality factor on simulated seismic waves: A case study of the 1994 Northridge earthquake
Zeng Qingpei, Wang Xiangchao, Wang Jinting
Abstract Full HTML(7) PDF[7920KB](37)
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.
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
Abstract Full HTML(106) PDF[7157KB](16)
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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Investigation on variations of apparent stress in the region in and around the rupture volume preceding the occurrence of the 2021 Alaska MW8.2 earthquake
Xuezhong Chen, Yane Li, Lijuan Chen
2022, 35(3): 147-160.   doi: 10.1016/j.eqs.2022.06.002
Abstract Full HTML(168) PDF[10315KB](46)
On July 29, 2021, a large earthquake of MW8.2 occurred south of the Alaska Peninsula. To investigate the spatial-temporal changes of crustal stress in the earthquake-stricken area before this event, we selected 159 earthquakes of 4.7 ≤ MW ≤ 6.9 that occurred in the epicentral region and its surroundings between January 1980 and June 2021 to study the temporal variation and spatial distribution of their apparent stress. In addition, we analyzed the correlation between seismic activities and Earth’s rotation and explored the seismogenic process of this earthquake. The crustal stress rose from January 2008 to December 2016. This period was followed by a sub-instability stage from January 2017 until the occurrence of the MW8.2 earthquake. The average rate of apparent stress change in the first five years of the stress increase period was roughly 2.3 times that in the last four years. The lateral distribution of the apparent stress shows that the areas with apparent stress greater than 1.0 MPa exhibited an expanding trend during the seismogenic process. The maximum apparent stress was located at the earthquake epicenter during the last four years. The distribution of the apparent stress in the E-W vertical cross section revealed that an apparent stress gap formed around the hypocenter during the first five years of the stress increase period, surrounded by areas of relatively high apparent stress. After the Alaska earthquake, most parts of this gap were filled in by aftershocks. The seismic activities during the sub-instability stage exhibited a significant correlation with Earth’s rotation.
A comparative study of seismic tomography models of the Chinese continental lithosphere
Xuezhen Zhang, Xiaodong Song, Jiangtao Li
2022, 35(3): 161-185.   doi: 10.1016/j.eqs.2022.05.005
Abstract Full HTML(89) PDF[18471KB](35)
The Chinese mainland is subject to complicated plate interactions that give rise to its complex structure and tectonics. While several seismic velocity models have been developed for the Chinese mainland, apparent discrepancies exist and, so far, little effort has been made to evaluate their reliability and consistency. Such evaluations are important not only for the application and interpretation of model results but also for future model improvement. To address this problem, here we compare five published shear-wave velocity models with a focus on model consistency. The five models were derived from different datasets and methods (i.e., body waves, surface waves from earthquakes, surface waves from noise interferometry, and full waves) and interpolated into uniform horizontal grids (0.5° × 0.5°) with vertical sampling points at 5 km, 10 km, and then 20 km intervals to a depth of 160 km below the surface, from which we constructed an averaged model (AM) as a common reference for comparative study. We compare both the absolute velocity values and perturbation patterns of these models. Our comparisons show that the models have large (> 4%) differences in absolute values, and these differences are independent of data coverage and model resolution. The perturbation patterns of the models also show large differences, although some of the models show a high degree of consistency within certain depth ranges. The observed inconsistencies may reflect limited model resolution but, more importantly, systematic differences in the datasets and methods employed. Thus, despite several seismic models being published for this region, there is significant room for improvement. In particular, the inconsistencies in both data and methodologies need to be resolved in future research. Finally, we constructed a merged model (ChinaM-S1.0) that incorporates the more robust features of the five published models. As the existing models are constrained by different datasets and methods, the merged model serves as a new type of reference model that incorporates the common features from the joint datasets and methods for the shear-wave velocity structure of the Chinese mainland lithosphere.
Emergence of non-extensive seismic magnitude-frequency distribution from a Bayesian framework
Ewin Sánchez
2022, 35(3): 186-192.   doi: 10.1016/j.eqs.2022.06.004
Abstract Full HTML(30) PDF[9275KB](8)
Non-extensive statistical mechanics has been used in recent years as a framework in order to build some seismic frequency-magnitude models. Following a Bayesian procedure through a process of marginalization, it is shown that some of these models can arise from the result shown here, which reinforces the relevance of the non-extensive distributions to explain the data (earthquake’s magnitude) observed during the seismic manifestation. In addition, it makes possible to extend the non-extensive family of distributions, which could explain cases that, eventually, could not be covered by the currently known distributions within this framework. The model obtained was applied to six data samples, corresponding to the frequency-magnitude distributions observed before and after the three strongest earthquakes registered in Chile during the late millennium. In all cases, fit parameters show a strong trend to a particular non-extensive model widely known in literature.
Gorkha earthquake (MW7.8) and aftershock sequence: A fractal approach
Ram Krishna Tiwari, Harihar Paudyal
2022, 35(3): 193-204.   doi: 10.1016/j.eqs.2022.06.001
Abstract Full HTML(77) PDF[9840KB](31)
On April 25, 2015, Nepal was struck by the MW7.8 Gorkha earthquake followed by an intense aftershock sequence. It was one of the most destructive earthquakes in the Himalayan arc, causing more than 8900 fatalities. In this study, we analyzed the dataset (429 events, magnitude of completeness (Mc) ≥ 4.2 local magnitude) of the first 45 days after the Gorkha earthquake to estimate the seismicity parameters b-value, D-value, and p-value. We used the maximum likelihood method to estimate the b-value and Omori-Utsu parameters, whereas the correlation integral method was applied to estimate the fractal dimension (D-value). The analysis was carried out using running and sliding window techniques. The lowest b-value (0.57 ± 0.04) and the highest D-value (1.65 ± 0.02) were computed at the time of the Gorkha earthquake, after which the b-value significantly increased to a maximum of 1.57. It again dropped to 0.93 at the time of the major aftershock on May 12, 2015. The D-value showed an initial quick drop and then decreased in a wavy pattern until the end of the study period, indicating the clustering and scattering of earthquakes in a fault region. The b-value contour map identified the eastern part of the study area as a high stress region (b = ~0.8), implying that the stress shifted to that region. The D-value contour map reveals that the seismogenic structure shifted from linear to planar in the region. The rate of aftershock decay (p = 0.86 ± 0.04) for a short period reflects that the level of stress decreased rapidly. This study helps to understand the level of stress and seismicity pattern of a region, which could be useful for aftershock studies.
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Correlation between the tilt anomaly on the vertical pendulum at the Songpan station and the 2021 MS7.4 Maduo earthquake in Qinghai province, China
Anfu Niu, Zhengyi Yuan, Jin Wei, Jing Zhao, Wei Yan
2022, 35(3): 205-212.   doi: 10.1016/j.eqs.2022.06.003
Abstract Full HTML(98) PDF[9634KB](42)
Understanding the relationship between precursory deformation anomalies and strong earthquakes is vital for physical earthquake prediction. Six months before the 2021 MS7.4 Maduo earthquake in Qinghai province, China, the vertical pendulum at the Songpan station was observed to tilt southward with a high rate and large amplitude. Studies conducted before the 2021 MS7.4 Maduo earthquake inferred the tilt anomaly to be an earthquake precursor. However, after the earthquake, the relation between the earthquake and the anomaly became controversial, partly because the Songpan station is located at a great distance from the epicenter. In this study, based on the deformation anomaly characteristics, relationship between the seismogenic fault and the fault near the anomaly, and associated quantitative analyses, we concluded that this anomaly may be associated with the 2021 MS7.4 Maduo earthquake. The duration and amplitude of this anomaly matched with the magnitude and epicenter distance of the Maduo earthquake. We have also interpreted the reason why the anomaly occurred near a fault that is obliquely intersected with the seismogenic fault and why the anomaly is located far from the earthquake epicenter.
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