Quasi-waveform seismic tomography of crustal structures in the capital circle region of China
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asi-waveform seismic tomography of crustal structures in the capital circle region of China 1
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Xueyuan HUANG , Dinghui YANG , Ping TONG , Yuan GAO , Yutao SHI & Hao WU 1
Department of Applied Statistics, School of Mathematics and Statistics, Beijing Technology and Business University, Beijing 100048, China; 2 Department of Mathematical Sciences, Tsinghua University, Beijing 100084, China; 3 Division of Mathematical Sciences, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore 637371, 4
Singapore; Asian School of the Environment, Nanyang Technological University, Singapore 637371, Singapore; 5 Institute of Earthquake Science, China Earthquake Administration, Beijing 100036, China
Received November 24, 2019; revised June 10, 2020; accepted July 20, 2020; published online November 2, 2020
Abstract Seismic tomography is one of the main tools to explore the interior of the earth. In this study, the quasi-waveform seismic tomographic method is used for the first time to reveal the crustal structures in the capital region of China. 3-D highresolution VP, VS and the Poisson’s ratio models are generated by inverting 29839 direct P- and 29972 direct S-wave traveltimes selected from 3231 local earthquakes. The results reveal strong crustal heterogeneities. The velocity anomalies at shallow depths are well consistent with surface geologic structures. The relatively low-velocity anomaly layer in the middle crust may be the result of multiple phases of tectonic activity. Earthquakes generally occurred on the boundaries of high- and low-velocity and Poisson’s ratio anomalies. There are obvious low-velocity anomalies below the hypocenters of the Tangshan earthquake and the historical Sanhe-Pinggu earthquake, implying the existence of fluids. The similar velocity structures around the hypocenters of the two earthquakes indicate that the occurrences of the two earthquakes may be related to the same mechanism. The highresolution velocity models provide important observational constraints on the small-scale heterogeneities and dynamic mechanism of the crust in the capital region of China. Keywords Citation:
Quasi-waveform inversion, Capital circle region, Seismic tomography, Crustal velocity structure, Heterogeneity
Huang X, Yang D, Tong P, Gao Y, Shi Y, Wu H. 2020. Quasi-waveform seismic tomography of crustal structures in the capital circle region of China. Science China Earth Sciences, 63, https://doi.org/10.1007/s11430-019-9663-4
1. Introduction On May 26, 2020, an M3.6 earthquake with a focal depth of 18 km occurred in Mentougou, west of Beijing City. In April 2019, two earthquakes, with magnitudes 2.9 (on April 7 at a focal depth of 17 km) and 3.0 (on April 14 at a focal depth of 19 km), occurred in Haidian and Huairou, respectively. These earthquakes could be felt in most of the urban areas of Beijing. The earthquakes, especially the two earthquakes occurred just one week apart in 2019, drew public attention * Corresponding author (email: [email protected])
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