Earthquake Science最新文献

In this study, the vertical components of broadband teleseismic P wave data recorded by China Earthquake Network are used to image the rupture processes of the February 6th, 2023 Turkish earthquake doublet via back projection analysis. Data in two frequency bands (0.5–2 Hz and 1–3 Hz) are used in the imaging processes. The results show that the rupture of the first event extends about 200 km to the northeast and about 150 km to the southwest, lasting ∼90 s in total. The southwestern rupture is triggered by the northeastern rupture, demonstrating a sequential bidirectional unilateral rupture pattern. The rupture of the second event extends approximately 80 km in both northeast and west directions, lasting ∼35 s in total and demonstrates a typical bilateral rupture feature. The cascading ruptures on both sides also reflect the occurrence of selective rupture behaviors on bifurcated faults. In addition, we observe super-shear ruptures on certain fault sections with relatively straight fault structures and sparse aftershocks.

High-quality datasets are critical for the development of advanced machine-learning algorithms in seismology. Here, we present an earthquake dataset based on the ChinArray Phase I records (X1). ChinArray Phase I was deployed in the southern north-south seismic zone (20° N–32° N, 95° E–110° E) in 2011–2013 using 355 portable broadband seismic stations. CREDIT-X1local, the first release of the ChinArray Reference Earthquake Dataset for Innovative Techniques (CREDIT), includes comprehensive information for the 105,455 local events that occurred in the southern north-south seismic zone during array observation, incorporating them into a single HDF5 file. Original 100-Hz sampled three-component waveforms are organized by event for stations within epicenter distances of 1,000 km, and records of ≥ 200 s are included for each waveform. Two types of phase labels are provided. The first includes manually picked labels for 5,999 events with magnitudes ≥ 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 of −1.6 to 7.6. These phases were picked using a recurrent neural network phase picker and screened using the 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 included for 31,273 Pg phases. The event and station locations are provided, so that deep learning networks for both conventional phase picking and phase association can be trained and validated. The CREDIT-X1local dataset is the first million-scale dataset constructed from a dense seismic array, which is designed to support various multi-station deep-learning methods, high-precision focal mechanism inversion, and seismic tomography studies. Additionally, owing to the high seismicity in the southern north-south seismic zone in China, this dataset has great potential for future scientific discoveries.

Lithospheric structure beneath the northeastern Qinghai-Xizang Plateau is of vital significance for studying the geodynamic processes of crustal thickening and expansion of the Qinghai-Xizang Plateau. 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 Qinghai-Xizang Plateau. 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 v_S, crustal thickness, and v_P/v_S structures in the Qinghai-Xizang Plateau were simultaneously derived from the joint inversion. The seismic images reveal that crustal thickness decreases outward from the Qinghai-Xizang Plateau. The stable interiors of the Ordos and Alxa blocks exhibited higher velocities and lower crustal v_P/v_S ratios. While, lower velocities and higher v_P/v_S 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, v_S, and v_P/v_S ratios suggest that whole lithospheric shortening is a plausible mechanism for crustal thickening in the Qinghai-Xizang Plateau, supporting the idea of coupled lithospheric-scale deformation in this region.

Large earthquakes frequently occur along complex fault systems. Understanding seismic rupture and long-term fault evolution requires constraining the geometric and material properties of fault zone structures. We provide a comprehensive overview of recent advancements in seismological methods used to study fault zone structures, including seismic tomography, fault zone seismic wave analysis, and seismicity analysis. Observational conditions limit our current ability to fully characterize fault zones, for example, insufficient imaging resolution to discern small-scale anomalies, incomplete capture of crucial fault zone seismic waves, and limited precision in event location accuracy. Dense seismic arrays can overcome these limitations and enable more detailed investigations of fault zone structures. Moreover, we present new insights into the structure of the Anninghe-Xiaojiang fault zone in the southeastern margin of the Qinghai-Xizang Plateau based on data collected from a dense seismic array. We found that utilizing a dense seismic array can identify small-scale features within fault zones, aiding in the interpretation of fault zone geometry and material properties.

The Indo-Gangetic Plain (IGP) is one of the most seismically vulnerable areas due to its proximity to the Himalayas. Geographic information system (GIS)-based seismic characterization of the IGP was performed based on the degree of deformation and fractal dimension. The zone between the Main Boundary Thrust (MBT) and the Main Central Thrust (MCT) in the Himalayan Mountain Range (HMR) experienced large variations in earthquake magnitude, which were identified by Number-Size (NS) fractal modeling. The central IGP zone experienced only moderate to low mainshock levels. Fractal analysis of earthquake epicenters reveals a large scattering of earthquake epicenters in the HMR and central IGP zones. Similarly, the fault fractal analysis identifies the HMR, central IGP, and south-western IGP zones as having more faults. Overall, the seismicity of the study region is strong in the central IGP, south-western IGP, and HMR zones, moderate in the western and southern IGP, and low in the northern, eastern, and south-eastern IGP zones.

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.

We developed a modified stochastic finite-fault method for estimating strong ground motions. An adjustment to the dynamic corner frequency was introduced, which accounted for the effect of the location of the subfault relative to the hypocenter and rupture propagation direction, to account for the influence of the rupture propagation direction on the subfault dynamic corner frequency. By comparing the peak ground acceleration (PGA), pseudo-absolute response spectra acceleration (PSA, damping ratio of 5%), and duration, the results of the modified and existing methods were compared, demonstrating that our proposed adjustment to the dynamic corner frequency can accurately reflect the rupture directivity effect. We applied our modified method to simulate near-field strong motions within 150 km of the 2008 M_W7.9 Wenchuan earthquake rupture. Our modified method performed well over a broad period range, particularly at 0.04–4 s. The total deviations of the stochastic finite-fault method (EXSIM) and the modified EXSIM were 0.1676 and 0.1494, respectively. The modified method can effectively account for the influence of the rupture propagation direction and provide more realistic ground motion estimations for earthquake disaster mitigation.

On August 6, 2023, a magnitude M_W5.5 earthquake struck Pingyuan County, Dezhou City, Shandong Province, China. This event was significant as no large earthquakes had been recorded in the region for over a century, and no active fault had been previously identified. This study collects 1309 P-wave arrival times and 866 S-wave arrival times from 74 seismic stations less than 200 km to the epicenter to constrain the spatial distribution of the mainshock and its 125 early aftershocks by the double difference earthquake relocation method, and selects 864 P-waveforms from 288 stations located within 800 km of the epicenter to constrain the focal mechanism solution of the mainshock through centroid moment tensor inversion. The relocation and the inversion indicate, the Pingyuan M_W5.5 earthquake was caused by a rupture on a buried fault, likely an extensive segment of the Gaotang fault. This buried fault exhibited a dip of approximately 75° to the northwest, with a strike of 222°, similar to the Gaotang fault. The rupture initiated at the depth of 18.6 km and propagated upward and northeastward. However, the ground surface was not broken. The total duration of the rupture was ∼6.0 s, releasing the scalar moment of 2.5895 × 10¹⁷ N·m, equivalent to M_W5.54. The moment rate reached the maximum only 1.4 seconds after the rupture initiation, and the 90% scalar moment was released in the first 4.6 s. In the first 1.4 seconds of the rupture process, the rupture velocity was estimated to be 2.6 km/s, slower than the local S-wave velocity. As the rupture neared its end, the rupture velocity decreased significantly. This study provides valuable insights into the seismic characteristics of the Pingyuan M_W5.5 earthquake, shedding light on the previously unidentified buried fault responsible for the seismic activity in the region. Understanding the behavior of such faults is crucial for assessing seismic hazards and enhancing earthquake preparedness in the future.

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 eigendisplacement 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.