Dizhi lixue xuebao (Apr 2021)
Numerical simulation of the present seismic risk of the HaiyuanLiupanshan fault zone
Abstract
In this study, the orthotropic theory-based characterization of fault deformation behavior was made, with the ratio of the shear modulus parallel to fault plane to the shear modulus of surrounding media as the inversion parameters and the present-day crust horizontal movement velocity field observed by GPS near the Haiyuan-Liupanshan fault as the constrain. We built a 3D finite element model, using the genetic algorithm, to estimate the shear moduls distribution parallel to the Haiyuan-Liupanshan fault plane. The inversion results show that the shear modulus parallel to the Liupanshan fault plane is close to that of the surrounding media, and the seismic activities are sparsely distributed along the fault plane, reflecting a small deformation difference on both sides of the Liupanshan near the fault, which is similar to the situation of the Longmenshan fault before the Wenchuan Earthquake. The fault zone may be in a state of strong locking. The shear modulus parallel to the fault plane of the Hanyuan fault in the narrow sense is much smaller than that of the surrounding media, all below 0.4, and the shear modulus within 0~5 km is larger than that of the deep, which may reflect that the entire fault has still been in post-earthquake adjustment since the Haiyuan 8.5-magnitude earthquake in 1920. The shear modulus of the Jinqianghe, Maomaoshan and Laohushan faults in the western section is relatively low at the shallow section of the faults (0~5 km), while the shear modulus of 5~20 km is relatively high. Combined with the fault surface seismic activity distribution characteristics, it is considered that creep slips may exist in the shallow sections of the Jingqianghe and Maomaoshan faults; however, there is strain energy accumulation in the depth of 5~20 km, which has the background of strong earthquake. Seismic activity of the Laohushan fault is relatively intensive from the surface to the deep, and there may be creep through, with a small probability of strong earthquake.
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