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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 and Uppermost Mantle Structure of the Northeastern Tibetan Plateau from Joint Inversion of Surface Wave Dispersions and Receiver Functions with P Velocity Constraints
Pei Zhang, Xiaodong Song, Jiangtao Li, Xingchen Wang, Xuezhen Zhang
Abstract Full HTML(0) PDF[11368KB](0)
Lithospheric structure beneath the northeastern Tibetan Plateau (NETP) is of vital significance for studying the geodynamic processes of crustal thickening and expansion of the Tibetan Plateau (TP).We conducted a joint inversion of receiver functions and surface wave dispersions with P-wave velocity constraints using data from the ChinArray II temporary stations deployed across the NETP. Prior to joint inversion, we applied the H-κ-c method (Li JT et al., 2019) to the receiver function data in order to correct for the back-azimuthal variations in the arrival times of Ps phases and crustal multiples caused by crustal anisotropy and dipping interfaces. High-resolution images of vS, crustal thickness, and vP/vS structures in the NETP were simultaneously derived from the joint inversion. The seismic images reveal that crustal thickness decreases outward from the NETP. The stable interiors of the Ordos and Alxa blocks exhibited higher velocities and lower crustal vP/vS ratios. While, lower velocities and higher vP/vS ratios were observed beneath the Qilian Orogen and Songpan–Ganzi terrane (SPGZ), which are geologically active and mechanically weak, especially in the mid-lower crust. Delamination or thermal erosion of the lithosphere triggered by hot asthenospheric flow contributes to the observed uppermost mantle low-velocity zones (LVZs) in the SPGZ. The crustal thickness, vS, and vP/vS ratios suggest that whole lithospheric shortening is a plausible mechanism for crustal thickening in the NETP, supporting the idea of coupled lithospheric-scale deformation in this region.
Transient postseismic slip and aftershock triggering: a case study of the 2008 MW7.9 Wenchuan Earthquake, China
Mengyu Xie, Baoping Shi, Lingyuan Meng
Abstract Full HTML(100) PDF[7736KB](17)
In this study, we investigate how a stress variation generated by a fault that experiences transient postseismic slip (TPS) affects the rate of aftershocks. First, we show that the postseismic slip from Rubin-Ampuero model is a TPS that can occur on the main fault with a velocity-weakening frictional motion, that the resultant slip function is similar to the generalized Jeffreys-Lomnitz creep law, and that the TPS can be explained by a continuous creep process undergoing reloading. Second, we obtain an approximate solution based on the Helmstetter-Shaw seismicity model relating the rate of aftershocks to such TPS. For the Wenchuan sequence, we perform a numerical fitting of the cumulative number of aftershocks using the Modified Omori Law (MOL), the Dieterich model, and the specific TPS model. The fitting curves indicate that the data can be better explained by the TPS model with a B/A ratio of approximately 1.12, where A and B are the parameters in the rate- and state-dependent friction law respectively. Moreover, the p and c that appear in the MOL can be interpreted by the B/A and the critical slip distance, respectively. Because the B/A ratio in the current model is always larger than 1, the model could become a possible candidate to explain aftershock rate commonly decay as a power law with a p-value larger than 1. Finally, the influence of the background seismicity rate r on parameters is studied; the results show that except for the apparent aftershock duration, other parameters are insensitive to r.
On the eigenvalues and eigendisplacement of the critical mode in horizontally layered media
Shaotong Wang, Laiyu Lu
Abstract Full HTML(5) PDF[8790KB](1)
Wave propagation in horizontally layered media is a classical problem in seismic-wave theory. In semi-infinite space, a nondispersive Rayleigh wave mode exists, and the eigen displacement decays exponentially with depth. In a layered model with increasing layer velocity, the phase velocity of the Rayleigh wave varies between the S-wave velocity of the bottom half-space and that of the classical Rayleigh wave propagated in a supposed half-space formed by the parameters of the top layer. If the phase velocity is the same as the P- or S-wave velocity of the layer, which is called the critical mode or critical phase velocity of surface waves, the general solution of the wave equation is not a homogeneous (expressed by trigonometric functions) or inhomogeneous (expressed by exponential functions) plane wave, but one whose amplitude changes linearly with depth (expressed by a linear function). Theories based on a general solution containing only trigonometric or exponential functions do not apply to the critical mode, owing to the singularity at the critical phase velocity. In this study, based on the classical framework of generalized reflection and transmission coefficients, the propagation of surface waves in horizontally layered media was studied by introducing a solution for the linear function at the critical phase velocity. Therefore, the eigenvalues and eigenfunctions of the critical mode can be calculated by solving a singular problem. The eigendisplacement characteristics associated with the critical phase velocity were investigated for different layered models. In contrast to the normal mode, the eigendisplacement associated with the critical phase velocity exhibits different characteristics. If the phase velocity is equal to the S-wave velocity in the bottom half-space, the eigendisplacement remains constant with increasing depth.
Joint inversion of Rayleigh group and phase velocities for S-wave velocity structure of the 2021 MS6.0 Luxian earthquake source area, China
Wei Xu, Pingping Wu, Dahu Li, Huili Guo, Qiyan Yang, Laiyu Lu, Zhifeng Ding
 doi: 10.1016/j.eqs.2023.09.003
Abstract Full HTML(172) PDF[13672KB](48)
On September 16, 2021, a MS6.0 earthquake struck Luxian County, one of the shale gas blocks in the Southeastern Sichuan Basin, China. To understand the seismogenic environment and its mechanism, we inverted a fine three-dimensional S-wave velocity model from ambient noise tomography using data from a newly deployed dense seismic array around the epicenter, by extracting and jointly inverting the Rayleigh phase and group velocities in the period of 1.6–7.2 s. The results showed that the velocity model varied significantly beneath different geological units. The Yujiasi syncline is characterized by low velocity at depths of ~ 3.0–4.0 km, corresponding to the stable sedimentary layer in the Sichuan Basin. The eastern and western branches of the Huayingshan fault belt generally show high velocity in the NE-SW direction, excepting several local low-velocity zones. The Luxian MS6.0 earthquake epicenter is located at the boundary between the high- and low-velocity zones, and the earthquake sequences expand eastward from the epicenter at depths of 3.0–5.0 km. Integrated with the velocity variations around the epicenter, distribution of aftershock sequences, and focal mechanism solution, it is speculated that the seismogenic mechanism of the main shock might be interpreted as the reactivation of pre-existing faults by hydraulic fracturing.
Seismic prompt gravity strain signals in a layered spherical Earth
Shenjian Zhang, Rongjiang Wang, Xiaofei Chen
 doi: 10.1016/j.eqs.2023.09.002
Abstract Full HTML(90) PDF[7558KB](13)
Seismic waves generated by an earthquake can produce dynamic perturbations in the Earth’s gravity field before the direct arrival of P-waves. Observations of these so-called prompt elasto-gravity signals by ground-based gravimeters and broadband seismometers have been reported for some large events, such as the 2011 MW9.1 Tohoku earthquake. Recent studies have introduced prompt gravity strain signals as a new type of observable seismic gravity perturbation that can be used to measure the spatial gradient of the perturbed gravity field. Theoretically, these types of signals can be recorded by in-development instruments termed gravity strainmeters, although no successful detection has been reported as yet. Herein, we propose an efficient approach for simulating prompt gravity strain signals based on a multilayered spherical Earth model. We compared the simulated waveforms with analytical solutions obtained from a homogeneous half-space model, which has been used in earlier studies. This comparison indicates that the effect of the Earth’s structural stratification is significant. With the help of the new simulation approach, we also demonstrated how the prompt gravity strain signals depend on the magnitude of the seismic source. We further conducted synthetic tests estimating earthquake magnitude using gravity strain signals to demonstrate the potential application of this type of signal in earthquake early warning systems. These results provide essential information for future studies on the synthesis and application of earthquake-induced gravity strain signals.
The Accessible Seismological Dataset of the high-density 2D seismic Array along Anninghe Fault
Weifan Lu, Zeyan Zhao, Han Yue, Shiyong Zhou, Jianping Wu, Xiaodong Song
Abstract Full HTML(6) PDF[14228KB](0)
The scientific goal of the Anninghe seismic array is to investigate the detailed geometry of the Anninghe fault and the velocity structure of the fault zone. This 2D seismic array is composed of 161 stations forming sub-rectangular geometry along the Anninghe fault, which covers 50 km and 150 km in the fault normal and strike directions, respectively, with ~ 5 km intervals. The data were collected between June 2020 and June 2021, with some level of temporal gaps. Two types of instruments, i.e. QS-05A and SmartSolo, are used in this array. Data quality and examples of seismograms are provided in this paper. After the data protection period ends (expected in June 2024), researchers can request a dataset from the National Earthquake Science Data Center.
High-resolution seismicity imaging and early aftershock migration of the 2023 Kahramanmaraş (SE Türkiye) MW7.9 & 7.8 earthquake doublet
Hongyang Ding, Yijian Zhou, Zengxi Ge, Tuncay Taymaz, Abhijit Ghosh, Haoyu Xu, Tahir Serkan Irmak, Xiaodong Song
 doi: 10.1016/j.eqs.2023.06.002
Abstract Full HTML(478) PDF[18798KB](164)
We build a high-resolution early aftershock catalog for the 2023 SE Türkiye seismic sequence with PALM, a seamless workflow that sequentially performs phase Picking, Association, Location, and Matched filter for continuous data. The catalog contains 29,519 well-located events in the two mainshocks rupture region during 2023-02-01-2023-02-28, which significantly improves the detection completeness and relocation precision compared to the public routine catalog. Employing the new PALM catalog, we analyze the structure of the seismogenic fault system. We find that the Eastern Anatolian Fault (EAF) that generated the first MW7.9 mainshock is overall near-vertical, whereas complexities are revealed in a small-scale, such as subparallel subfaults, unmapped branches, and stepovers. The seismicity on EAF is shallow (<15 km) and concentrated in depth distribution, indicating a clear lock-creep transition. In contrast, the Sürgü Fault (SF) that is responsible for the second MW7.8 mainshock is shovel-shaped for the nucleation segment and has overall low dip angles (~40–80°). Aftershocks on the SF distribute in a broad range of depth, extending down to ~35 km. We also analyze the temporal behavior of seismicity, discovering no immediate foreshocks within ~5 days preceding the first mainshock, and no seismic activity on the SF before the second mainshock.
CREDIT-X1local: A reference dataset for machine learning seismology from ChinArray in southwest China
Lu Li, Weitao Wang, Ziye Yu, Yini Chen
 doi: 10.1016/j.eqs.2023.08.001
Abstract Full HTML(358) PDF[10939KB](41)
High-quality datasets are critical for developing advanced machine learning algorithms in seismology. Here we present an earthquake dataset built from the records of ChinArray Phase I (X1), which was deployed in southern North-South Seismic Zone during 2011-2013 with 355 portable broadband seismic stations. As the first release of ChinArray Reference Earthquake Dataset for Innovative Technique (CREDIT), CREDIT-X1local organizes comprehensive information of 105,455 local events occurred in southern North-South Seismic Zone (20°-32°N, 95°-110°E) during array observation in one single HDF5 file. The original 100 Hz sampled three component waveforms are organized by each event for stations with epicenter distances up to 1,000 km, each waveform contains record of at least 200 seconds. Two types of phase labels are provided. The first includes manually picked labels for 5,999 events with magnitudes larger than 2.0, providing 66,507 Pg, 42,310 Sg, 12,823 Pn and 546 Sn phases. The second contains automatically labeled phases for 105,442 events with magnitudes ranging from −1.6 to 7.6. These phases are picked using a RNN phase picker and screened using corresponding travel-time curves, resulting in 1,179,808 Pg, 884,281 Sg, 176,089 Pn and 22,986 Sn phases. Additionally, first-motion polarities are also attached to 31,273 Pg phases. The events and station locations are provided, so that deep learning networks for both the conventional phase-picking and phase association can be trained and validated. CREDIT-X1local dataset is the first million-scale dataset built from the dense seismic array, which can serve as a basis for various multi-station deep-learning methods and high-precision focal mechanism inversion and seismic tomography studies. Additionally, benefiting from the high seismicity at the southern North-South Seismic Zone in China, CREDIT-X1local dataset has great potential for scientific discoveries in the future.
Intrinsic and scattering attenuations of the Sichuan-Yunnan region in China from S coda waves
Tian Li, Lei Zhang, Xiaodong Song, Qincai Wang, Xinyu Jiang, Jinchuan Zhang, Hanlin Chen
Abstract Full HTML(45) PDF[16511KB](4)
Seismic attenuation is a fundamental property of the earth's media. Attenuation structure for the complicated geological structures with strong seismicity in the Sichuan-Yunnan region is poorly studied. In this study, we collected 108,399 waveforms of 11,517 local small earthquakes with magnitudes between 1.5 and 3.5 from January 2014 to September 2021 in the Sichuan-Yunnan region and its adjacent areas. We employed an envelope inversion technique for separating the intrinsic and scattering attenuations of the S coda wave, and obtained the intrinsic and scattering attenuation structures for frequencies between 0.25 and 8.00 Hz. The attenuation structures correlate well with the geological units, and some major faults mark the attenuation variations where historic large earthquakes have occurred. The regional average attenuation shows a negative frequency dependence. The average scattering attenuation has a faster descending rate the average intrinsic attenuation, and is dominant at low frequencies, while at high frequencies the average intrinsic attenuation is stronger. The lateral variation in the intrinsic attenuation is consistent with the variation in heat flow, the scattering attenuation may be related to the scatter distribution and size. The total attenuation is consistent with the previous studies in this region, and the separate intrinsic and scattering attenuation may be useful in understanding regional tectonics and important in earthquake prevention and disaster reduction.
Analysis of faulting destruction and water supply pipeline damage from the first mainshock of the February 6, 2023 Turkey earthquake doublet
Fan Xiaoqing, Zhang Libao, Wang Juke, Ren Yefei, Liu Aiwen
Abstract Full HTML(92) PDF[15881KB](14)
In 2023, two consecutive earthquakes exceeding a magnitude of 7 occurred in Turkey, causing severe casualties and economic losses. The damage to critical urban infrastructure and building structures, including highways, railroads, and water supply pipelines, was particularly severe in areas where these structures intersected the seismogenic fault. Critical infrastructure projects that traverse active faults are susceptible to the influence of fault movement, pulse velocity, and ground motions. In this study, we used a unique approach to analyze the acceleration records obtained from the seismic station array (9 strong ground motion stations) located along the East Anatolian Fault (the seismogenic fault of the Mw 7.8 mainshock of the 2023 Turkey earthquake doublet). The acceleration records were filtered and integrated to obtain the velocity and displacement time histories. We used the results of an on-site investigation, jointly conducted by China Earthquake Administration and Turkey’s AFAD, to analyze the distribution of PGA, PGV, and PGD recorded by the strong motion array of the East Anatolian Fault. We found that the maximum horizontal PGA in this earthquake was 3.0 g, and the maximum co-seismic surface displacement caused by the East Anatolian Fault rupture was 6.50 m. As the fault rupture propagated southwest, the velocity pulse caused by the directional effect of the rupture increased gradually, with the maximum PGA reaching 162.3 cm/s. We also discussed the seismic safety of critical infrastructure projects traversing active faults, using two case studies of water supply pipelines in Turkey that were damaged by earthquakes. We used a three-dimensional finite element model of the PE (polyethylene)water pipeline at the Islahiye State Hospital and fault displacement observations obtained through on-site investigation to analyze pipeline failure mechanisms. We further investigated the effect of the fault-crossing angle on seismic safety of a pipeline, based on our analysis and the failure performance of the large-diameter Thames Water pipeline during the 1999 Kocaeli earthquake. The seismic method of buried pipelines crossing the fault were summarized.
Apparent stress as an indicator of stress meta-instability: The 2021 MS6.4 Yangbi earthquake in Yunnan, China
Yane Li, Xuezhong Chen, Lijuan Chen, Yaqiong Ren, Xiangyun Guo
Abstract Full HTML(43) PDF[8312KB](7)
Investigating spatiotemporal changes in crustal stress associated with major earthquakes has implications for understanding seismogenic processes. However, in individual earthquake cases, the characteristics of the stress after it reaches its maximum value are rarely discussed. In this study, we use the 2021 MS6.4 Yangbi earthquake in Yunnan, China and events of magnitudes ML ≥ 3.0 occurred in the surrounding area in the previous 11 years to investigate the spatiotemporal evolution of apparent stress. The results indicate that apparent stress began to increase in January 2015 and reached a maximum in January 2020. Apparent stress then remained at a high level until October 2020, after which it declined considerable. We suggest that the stress was in the accumulation stage from January 2015 to January 2020, and entered the meta-instability stage after October 2020. During the meta-instability stage, the zone of decreasing stress expanded continuously and the apparent stress increased around the Yangbi earthquake source region. These features are generally consistent with the results of laboratory rock stress experiments. We propose that apparent stress can be a good indicator for determining whether the stress at a specific location has entered the meta-instability stage and may become the epicenter of an impending strong earthquake.
Theories and applications of earthquake-induced gravity variation: Advances and perspectives
He Tang, Wenke Sun
Abstract Full HTML(134) PDF[14870KB](32)
Earthquake-induced gravity variation refers to changes in the earth’s gravity field associated with seismic activities. In recent years, development in the theories of earthquake-induced gravity variation has greatly promoted seismic deformation research, laying a solid theoretical foundation for the interpretation and application of seismological gravity monitoring. Traditional terrestrial gravity measurements continue to play a significant role in studies of interseismic, co-seismic, and post-seismic gravity field variations. For instance, superconducting gravimeter networks can detect co-seismic gravity change at the sub-micro Gal level. At the same time, the successful launch of satellite gravity missions (e.g., the Gravity Recovery and Climate Experiment or GRACE) has also facilitated applied studies of the gravity variation associated with large earthquakes, and several remarkable breakthroughs have been achieved. The progress in gravity observation technologies (e.g., GRACE and superconducting gravimetry) and advances in the theories of earthquake-induced gravity variation have jointly promoted seismic deformation studies and raised many new research topics. For example, superconducting gravimetry has played an important role in analyses of episodic tremor, slow-slip events, and interseismic strain patterns; the monitoring of earthquake-induced transient gravity signals and related theories have provided a new perspective on earthquake early warning systems; the mass transport detected by the GRACE satellites several months before an earthquake has brought new insights into earthquake prediction methods; the use of artificial intelligence to automatically identify tiny gravity change signals is a new approach to accurate and rapid determination of earthquake magnitude and location. Overall, many significant breakthroughs have been made in recent years in the study of earthquake-induced gravity changes, in terms of the theory, application, and observation measures. This article summarizes the progress made in the theoretical, observational, and applied research of earthquake-induced gravity variation, with the aim of providing a reference for seismologists and geodetic researchers studying the phenomenon of earthquake-induced gravity variation, advances in related theories and applications, and future research directions in this discipline.
Topography of the 660-km Discontinuity within the Izu–Bonin Subduction Zone and Evidence of Slab Penetration near the Bonin Super Deep Earthquake (~680 km)
Gang Hao
Abstract Full HTML(109) PDF[12405KB](7)
The Izu–Bonin subduction zone in the Northwest Pacific is an ideal location for understanding mantle dynamics such as cold lithosphere subduction. The slab produces a lateral thermal anomaly, inducing local topographic changes at the boundary of a post-spinel phase transformation, considered to be the origin of the ‘660-km discontinuity.’ In this study, the short-period (1~2 Hz) S-to-P conversion phase S660P was used to obtain the fine-scale structure of the discontinuity. More than 100 earthquakes that occurred from the 1980s to the 2020s and were recorded by high-quality seismic arrays in the United States and Europe were analyzed. A discontinuity in the ambient mantle with an average depth of ~670 km was found beneath the 300–400-km event zone in the northern Bonin region near 33°N. Meanwhile, the ‘660-km discontinuity’ has been pushed upward, away from the slab, possibly because of a hot upwelling mantle plume. In the central part of the subduction zone, the 660-km discontinuity is depressed to an average depth of 690 ± 5 km within the slab at approximately 150 km below the coldest slab core, indicating a 300 ± 100 °C cold anomaly estimated using a post-spinel transformation Clapeyron slope of −2.0 ± 1.0 MPa/K. In southern Bonin near 28°N, the discontinuity was found to be further depressed at an average depth of 695 ± 5 km below the deepest event and with a focal depth of ~550 km. The discontinuity is located where the slab bends abruptly to become sub-horizontal toward the west-southwest. Near the zone of the isolated Bonin Super Deep Earthquake, which occurred at ~680 km on May 30, 2015, the discontinuity is depressed to ~700 km, suggesting a near-vertical penetrating slab and an S-to-P conversion in the coldest slab core, where a large low-temperature anomaly should exist.
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(820) PDF[3199KB](359)
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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Simulating the strong ground motion of the 2022 MS6.8 Luding, Sichuan, China Earthquake
Libao Zhang, Lei Fu, Aiwen Liu, Su Chen
2023, 36(4): 283-296.   doi: 10.1016/j.eqs.2023.05.001
Abstract Full HTML(370) PDF[5703KB](70)
Stochastic finite-fault simulations are effective for simulating ground motions and are widely used in engineering to determine the impacts of ground motion and develop relevant predictive equations. In this study, the source, path, and site amplification coefficient of western Sichuan Province, China, and stochastic finite-fault simulations were used to simulate the acceleration time series, Fourier amplitude spectra, and 5% damped response spectra of 28 strong-motion stations with rupture distances within 300 km of the 2022 MS6.8 Luding earthquake. The simulation results of 14 stations at rupture distances of 45–185 km match the observation. However, the simulation results of 3 near- and 6 far-field stations at rupture distances of 12–36 km and 222–286 km, respectively, were obviously deviated from the observations. Simulation results of the near-field stations are larger than the observations at high frequencies (>6 Hz). The discrepancy likely comes from the nonlinear site effect of near-field stations, which reduced the site amplification at high frequencies. Simulation result of the far-field stations is smaller than the observation at frequencies above 1 Hz. As these stations are located close to the Longmenshan Fault Zone (LFZ), thus, we obtained a new quality factor (Q) from data of historical events and stations located around LFZ. Using the new Q value, the discrepancies of the high-frequency simulation results of the far-field stations were corrected. This result indicated that the laterally varying Q values can be used to address the impact of strong crustal lateral heterogeneity on simulation.
Upper crustal deformation characteristics in the northeastern Tibetan Plateau and its adjacent areas revealed by GNSS and anisotropy data
Shuyu Li, Yuan Gao, Honglin Jin
2023, 36(4): 297-308.   doi: 10.1016/j.eqs.2023.05.003
Abstract Full HTML(213) PDF[5381KB](35)
The northeastern part of the Tibetan Plateau is a region where different tectonic blocks collide and intersect, and large earthquakes are frequent. Global Navigation Satellite System (GNSS) observations show that tectonic deformation in this region is strong and manifests as non-uniform deformation associated with tectonic features. S-wave splitting studies of near-field seismic data show that seismic anisotropy parameters can also reveal the upper crustal medium deformation beneath the reporting station. In this paper, we summarize the surface deformation from GNSS observations and crustal deformation from seismic anisotropy data in the northeastern Tibetan Plateau. By comparing the principal compressive strain direction with the fast S-wave polarization direction of near-field S-wave splitting, we analyzed deformation and its differences in surface and upper crustal media in the northeastern Tibetan Plateau and adjacent areas. The principal compressive strain direction derived from GNSS is generally consistent with the polarization direction of fast S-waves, but there are also local tectonic regions with large differences between them, which reflect the different deformation mechanisms of regional upper crustal media. The combination of GNSS and seismic anisotropy data can reveal the depth variation characteristics of crustal deformation and deepen understanding of three-dimensional crustal deformation and the deep dynamical mechanisms underlying it. it.
Data Products
An accessible strong-motion dataset (PGA, PGV, and site vS30) of 2022 MS6.8 Luding, China Earthquake
Jian Zhou, Nan Xi, Chuanchuan Kang, Li Li, Kun Chen, Xin Tian, Chao Wang, Jifeng Tian
2023, 36(4): 309-315.   doi: 10.1016/j.eqs.2023.01.001
Abstract Full HTML(404) PDF[2581KB](71)
A MS6.8 earthquake occurred on 5th September 2022 in Luding county, Sichuan, China, at 12: 52 Beijing Time (4:52 UTC). We complied a dataset of PGA, PGV, and site vS30 of 73 accelerometers and 791 Micro-Electro-Mechanical System (MEMS) sensors within 300 km of the epicenter. The inferred vS30 of 820 recording sites were validated. The study results show that: (1) The maximum horizontal PGA and PGV reaches 634.1 Gal and 71.1 cm/s respectively. (2) Over 80% of records are from soil sites. (3) The vS30 proxy model of Zhou J et al. (2022) is superior than that of Wald and Allen (2007) and performs well in the study area. The dataset was compiled in a flat file that consists the information of strong-motion instruments, the strong-motion records, and the vS30 of the recording sites. The dataset is available at https://www.seismisite.net.
Special Focus/Rapid Communication
Rapid source inversions of the 2023 SE Türkiye earthquakes with teleseismic and strong-motion data
Chenyu Xu, Yong Zhang, Sibo Hua, Xu Zhang, Lisheng Xu, Yuntai Chen, Tuncay Taymaz
2023, 36(4): 316-327.   doi: 10.1016/j.eqs.2023.05.004
Abstract Full HTML(407) PDF[4595KB](98)
We conducted rapid inversions of rupture process for the 2023 earthquake doublet occurred in SE Türkiye, the first with a magnitude of MW7.8 and the second with a magnitude of MW7.6, using teleseismic and strong-motion data. The teleseismic rupture models of the both events were obtained approximately 88 and 55 minutes after their occurrences, respectively. The rupture models indicated that the first event was an asymmetric bilateral event with ruptures mainly propagating to the northeast, while the second one was a unilateral event with ruptures propagating to the west. This information could be useful in locating the meizoseismal areas. Compared with teleseismic models, the strong-motion models showed relatively higher resolution. A noticeable difference was found for the MW7.6 earthquake, for which the strong-motion models shows a bilateral event, rather than a unilateral event, but the dominant rupture direction is still westward. Nevertheless, all strong-motion models are consistent with the teleseismic models in terms of magnitudes, durations, and dominant rupture directions. This suggests that both teleseismic and strong-motion data can be used for fast determination of major source characteristics. In contrast, the strong-motion data would be preferable in future emergency responses since they are recorded earlier and have a better resolution ability on the source ruptures.
Pulse-like ground motion observed during the 6 February 2023 MW7.8 Pazarcık Earthquake (Kahramanmaraş, SE Türkiye)
Fan Wu, Junju Xie, Zhao An, Chenghao Lyu, Tuncay Taymaz, Tahir Serkan Irmak, Xiaojun Li, Zengping Wen, Baofeng Zhou
2023, 36(4): 328-339.   doi: 10.1016/j.eqs.2023.05.005
Abstract Full HTML(651) PDF[5432KB](154)
In this study, we analyzed 100 three-component strong ground motion records observed within 200 km of the causative fault of the 6 February 2023 MW7.8 Pazarcık (Kahramanmaraş) Earthquake in SE Türkiye. The wavelet method was utilized to identify and analyze the characteristics of pulse-like ground motions in the near-fault region, while considering the uncertainty of the pulse orientation during the analysis. Our investigation focused on the effects of the focal mechanism and rupture process on the spatial distribution, pulse orientation, and maximum pulse direction of the observed pulse-like ground motion. We also analyzed the amplitude and period of the observed ground pulses and the effect of long-period amplification on the ground motion response spectra. Our results indicated the following: (1) A total of 21 typical ground velocity pulses were observed during this earthquake, exhibiting complex characteristics due to the influence of the strike-slip mechanism and rupture directivity. Most ground pulses (17 out of 21) were recorded within 20 km of the fault, in a wide range of orientations, including normal and parallel to the fault direction. The waveforms exhibited unidirectional features, indicating the effects of left-lateral fault slip. Distinct pulses observed more than 20 km from the fault were mainly oriented normal to the fault. The waveforms were bidirectional with double- or multi-round trips as a result of rupture directivity. (2) The amplitudes of the observed pulses ranged from 30.5 to 220.0 cm/s, with the largest peak velocity of 220.0 cm/s observed at Station 3138. The pulse periods ranged from 2.3 to 14.5 s, with the longest pulse period of 14.5 s observed at Station 3116. The amplitude and period of the pulses observed during this earthquake were comparable to those of similar-magnitude global earthquakes. The amplitude of the pulses decreased significantly with increasing fault distance, whereas the pulse period was not significantly affected by the fault distance. (3) Compared with non-pulse records, the velocity pulse records had a pronounced amplification effect on the acceleration response spectra near the pulse period, with factors ranging from 2.1 to 5.8. The larger velocity pulses also significantly amplified the velocity response spectra, particularly over the long periods. This significant amplification effect of the pulses on the response spectra leads to empirical models underestimating the long-period earthquake ground motion.
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