Crustal P-wave tomographic study of the Yishu fault zone

doi:10.13745/j.esf.sf.2022.2.62

Abstract

Abstract:

The Yishu Fault zone is an important fault zone in the eastern North China Craton and historically experienced a magnitude 8¹/₂ earthquake. To protect against future strong earthquakes and reduce earthquake damage, it is helpful to study the regional seismic velocity model so as to improve the accuracy of seismogram and rapid reporting of seismic intensity. In this study we collect digital seismic data recorded between 2008-2020 in the Yishu Fault zone, and preprocess the data using declustering and normal distribution travel-time selection techniques to obtain the local epicenter parameters and travel-time data; then by tomographic inversion using FMTOMO software we obtained three-dimensional seismic velocity model of the Yishu Fault zone. According to the 3D model, the velocity distribution features in the near surface layer are closely related to the geological structural units, as the fold belt and bedrock outcropping areas often present high velocity distribution while low velocity distribution is generally associated with the sag or sea area with thick soil layers. In the middle crustal layer, seismicity is closely related to the velocity distribution features, and the earthquake epicenters are often densely distributed in the transition zone between high and low velocities. At the Moho depth, velocity distribution in the Yishu belt shows segmental differences and differs on both sides of the belt, this could mean that the fault zone reaches the mantle. High velocity distribution is present in the middle and southern part of the Yishu belt, which may be related to the regional upwelling of mantle material, or may constitute the seismogenic background of strong earthquakes. In the Tancheng area, high velocity anomalies are observed from the earth’s surface to the top of the mantle, suggesting that high stress could accumulate in this area, and an earthquake of magnitude 8 or above might occur, but the recurrence period is considered very long.

Key words: Shandong, Yishu Fault, P-wave, tomography

CLC Number:

P315.2

CUI Xin, SONG Xiuqing, SHI Yaolin, YIN Haitao, ZHU Yuanqing, DONG Tengchao. Crustal P-wave tomographic study of the Yishu fault zone[J]. Earth Science Frontiers, 2023, 30(2): 272-281.

Figures/Tables 8

Fig.1 Tectonic setting and distribution of observation stations in the study area

Fig.2 Earthquake epicenter distribution map

Fig.3 (a) Quantity and (b-i) angle distributions of seismic rays

Fig.4 Results of checkerboard tests

Fig.5 Seismic one-dimensional velocity model

Fig.6 Trade-off L-curve between model and travel-time residual variances

Fig.7 Three-dimensional P-wave velocity distribution around the Yishu Fault zone (horizontal slice)

Fig.8 Three-dimensional P-wave velocity distribution around the Yishu Fault zone (vertical slice)

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