Earthquake Research Advances最新文献

With the continuous development of the oblique photography technique, it has been used more and more widely in the field of geological disasters. It can quickly obtain the three-dimensional (3D) real scene model of dangerous mountainous areas under the premise of ensuring the safety of personnel while restoring the real geographic information as much as possible. However, geological disaster areas are often accompanied by many adverse factors such as cliffs and dense vegetation. Based on this, the paper introduced the flight line design of oblique photogrammetry, analyzed the multi-platform data fusion processing, studied the multi-period data dynamic evaluation technology and proposed the application methods of data acquisition, early warning, disaster assessment and decision management suitable for geological disaster identification through the analysis of actual cases, which will help geologists to plan and control geological work more scientifically and rationally, improve work efficiency and reduce the potential personnel safety hazards in the process of geological survey, to offer technical support to the application of oblique photogrammetry in geological disaster identification and decision making and provide the scientific basis for personal and property safety protection and later-stage geological disaster management in disaster areas.

On December 18, 2023, the M_S 6.2 Jishishan earthquake occurred in the northeastern region of the Qinghai-Xizang Plateau, causing heavy casualties and property damage in Gansu and Qinghai Provinces. In this study, we integrate space imaging geodesy, finite fault inversion, and back-projection methods to decipher its rupture property, including fault geometry, coseismic slip distribution, rupture direction, and propagation speed. The results reveal that the seismogenic fault dips to the southwest at an angle of 29°. The major slip asperity is dominated by reverse slip and is concentrated within a depth range of 7–16 ​km, which explains the significant uplift near the epicenter observed by both the Sentinel-1 ascending and descending InSAR data. Moreover, the teleseismic array waveforms indicate a northwest propagating rupture with an overall slow rupture velocity of ∼1.91 ​km/s (AK array) or 1.01 ​km/s (AU array).

Shear wave splitting (SWS) is regarded as the most effective geophysical method to delineate mantle flow fields by detecting seismic azimuthal anisotropy in the earth's upper mantle, especially in tectonically active regions such as subduction zones. The Aleutian-Alaska subduction zone has a convergence rate of approximately 50 ​mm/yr, with a trench length reaching nearly 2800 ​km. Such a long subduction zone has led to intensive continental deformation and numerous strong earthquakes in southern and central Alaska, while northern Alaska is relatively inactive. The sharp contrast makes Alaska a favorable locale to investigate the impact of subduction on mantle dynamics. Moreover, the uniqueness of this subduction zone, including the unusual subducting type, varying slab geometry, and atypical magmatic activity and composition, has intrigued the curiosity of many geoscientists. To identify different sources of seismic anisotropy beneath the Alaska region and probe the influence of a geometrically varying subducting slab on mantle dynamics, extensive SWS analyses have been conducted in the past decades. However, the insufficient station and azimuthal coverage, especially in early studies, not only led to some conflicting results but also strongly limited the in-depth investigation of layered anisotropy and the estimation of anisotropy depth. With the completion of the Transportable Array project in Alaska, recent studies have revealed more detailed mantle structures and characteristics based on the dense station coverage and newly collected massive seismic data. In this study, we review significant regional- and continental-scale SWS studies in the Alaska region and conclude the mantle flow fields therein, to understand how a geometrically varying subducting slab alters the regional mantle dynamics. The summarized mantle flow mechanisms are believed to be conducive to the understanding of seismic anisotropy patterns in other subduction zones with a complicated tectonic setting.

Due to the joint development characteristic and macropore structure of loess, it is easy to cause structure collapse under earthquake or artificial vibration. The study on the loess disaster effect and its mechanism under earthquake action is insufficient due to its complexity. Hence, to study the deformation and mechanical properties more accurately, the dynamic characteristics of saturated remolded loess under cyclic dynamic load were tested using a GDS dynamic triaxial instrument in this paper. The test results show that strain and pore water pressure increase gradually at different rates with the development of vibration, and there is an obvious inflection point in the time-history curve of both. When the number of vibrations (N) exceeds this point, the strain increases rapidly, and pore water pressure tends to be stable. Under the action of large amplitude and low-frequency dynamic load, the strain and pore water pressure increase rapidly with fewer vibrations and the deviator stress (q) decreases rapidly, while the sample achieves damage faster with the increase of amplitude. During the application of a dynamic load, the effective stress (p) gradually decreases and its rate of change slows down. Finally, when the saturated remolded loess is subjected to a constant-amplitude dynamic load, the combination of large amplitude and low frequency leads to the failure of the sample in the shortest time.

The development of machine learning technology enables more robust real-time earthquake monitoring through automated implementations. However, the application of machine learning to earthquake location problems faces challenges in regions with limited available training data. To address the issues of sparse event distribution and inaccurate ground truth in historical seismic datasets, we expand the training dataset by using a large number of synthetic envelopes that closely resemble real data and build an earthquake location model named ENVloc. We propose an envelope-based machine learning workflow for simultaneously determining earthquake location and origin time. The method eliminates the need for phase picking and avoids the accumulation of location errors resulting from inaccurate picking results. In practical application, ENVloc is applied to several data intercepted at different starting points. We take the starting point of the time window corresponding to the highest prediction probability value as the origin time and save the predicted result as the earthquake location. We apply ENVloc to observed data acquired in the southern Sichuan Basin, China, between September 2018 and March 2019. The results show that the average difference with the catalog in latitude, longitude, depth, and origin time is 0.02°, 0.02°, 2 ​km, and 1.25 ​s, respectively. These suggest that our envelope-based method provides an efficient and robust way to locate earthquakes without phase picking, and can be used in earthquake monitoring in near-real time.

On December 18, 2023, the Jishishan area in Gansu Province was jolted by a M_S 6.2 earthquake, which is the most powerful seismic event that occurred throughout the year in China. The earthquake occurred along the NW-trending Lajishan fault (LJSF), a large tectonic transformation zone. After this event, China Earthquake Networks Center (CENC) has timely published several reports about seismic sources for emergency responses. The earthquake early warning system issued the first alert 4.9 ​s after the earthquake occurrence, providing prompt notification that effectively mitigated panics, injuries, and deaths of residents. The near real-time focal mechanism solution indicates that this earthquake is associated with a thrust fault. The distribution of aftershocks, the rupture process, and the recorded amplitudes from seismic monitoring and GNSS stations, all suggest that the mainshock rupture predominately propagates to the northwest direction. The duration of the rupture process is ∼12 ​s, and the largest slip is located at approximately 6.3 ​km to the NNW from the epicenter, with a peak slip of 0.12 ​m at ∼8 ​km depth. Seismic station N0028 recorded the highest instrumental intensity, which is 9.4 on the Mercalli scale. The estimated intensity map shows a seismic intensity reaching up to IX near the rupture area, consistent with field survey results. The aftershocks (up to December 22, 2023) are mostly distributed in the northwest direction within ∼20 ​km of the epicenter. This earthquake caused serious casualties and house collapses, which requires further investigations into the impact of this earthquake.

We have developed an automatic regional focal mechanism inversion system based on the Earthquake Rapid Report (ERR) system and the real-time three-component seismic waveform stream of 1 000 broadband seismic stations provided by the China Earthquake Networks Center (CENC). The system can rapidly provide a double couple solution and centroid depth within 5–15 ​min after receiving earthquake information from the ERR system. The data processing is triggered by earthquake information obtained from the ERR system. The system is capable of determining the focal mechanism of all shallow-depth earthquakes in the Chinese mainland with a magnitude of 5.5–6.5. It utilizes waveform data recorded by seismic stations located within 500 ​km from the epicenter, enabling the reporting of a focal mechanism solution within 5–15 ​min of an earthquake occurrence. Additionally, the system can assign a corresponding grade (A B C) to the focal mechanism solution. We processed a total of 301 earthquakes that occurred from 2021 to June 2022, and after the quality control, 166 of them were selected. These selected solutions were manually checked, and 160 of them were compiled in a focal mechanism catalog. This catalog can be conveniently downloaded online via the Internet. The automatic focal mechanism solution of earthquakes in eastern China exhibits a good agreement with that provided by the Global Centroid Moment Tensor (GCMT), when available. The average Kagan angle between this catalog and GCMT is 22°, and the average difference in M_W is 0.17. Furthermore, compared with GCMT, the minimum magnitude of our catalog has been reduced from approximately 5.0 to 4.0. The correlation between the centroid depth and crustal thickness in the Chinese mainland confirms the distribution of the centroid depth.