The study of crustal thickness and Poisson s ratio on both sides of the Lijiang-Xiaojinhe fault by H-κ-c method
Using teleseismic waveform data recorded by 156 dense stations composed of different networks,we extracted P-wave receiver functions and calculated the crustal thickness and Poisson's ratio on both sides of the Lijiang-Xiaojinhe fault via the H-κ-c method.We analyzed and discussed the characteristics of the crustal material composition,seismogenic environment and seismic hazard potential of the Lijiang-Xiaojinhe fault.The results show that the crustal thickness gradually decreases from～70 km northwest to～39 km southeast in the study area.The crust is thicker to the north of 27°N and relatively thinner to the south.The Moho surface in the Yanyuan-Panzhihua zone is significantly uplifted.High Poisson's ratios(σ＞0.28)are found beneath the Xiangcheng—Derong—Xianggelila,Mianning,Lijiang—Heqing—Ninglang and Yanyuan-Panzhihua-Dechang areas.Low Poisson's ratios(σ＜0.26)are found beneath the districts between the Muli fault,Yanyuan fault and Jinhe—Qinghe fault,and the ares nearby Lancangjiang fault and Chenghai fault.Considering the characteristics of high heat flow and low S-wave velocity,we conclude that the ductile materials in the lower crust extruded laterally from the Tibetan Plateau caused the high Poisson's ratios and thick crust beneath Xiangcheng-Derong-Xianggelila and Mianning,and squeezed into Lijiang-Heqing-Ninglang along nearly NS or NW-trending faults.According to the properties of low heat flow,high Poisson's ratio,high density and high P-wave velocity,we speculate that the local uplift of the Moho in the Yanyuan-Panzhihua area is associated with the Permian mantle plume,that magmatic underplating resulted in the thinning of the crust,and that frozen magma led to a mafic or ultramafic layer at the base of the crust in the Yanyuan-Panzhihua-Dechang zone.The low crustal flow that is related to the southeastward escape of the Tibetan Plateau is blocked by the inner zone of the Emeishan Large Igneous Province,which turns southwest along the Lijiang-Xiaojinhe fault.Most Ms≥5.0 earthquakes occurred in the high-gradient belts of the Moho surface,in areas with high Poisson's ratios and in transition zones with low-high Poisson's ratios.The Muli-Mianning segment of the Lijiang-Xiaojinhe fault and the intersection of the Daju fault and Lijiang-Xiaojinhe fault are the junctions of high and low Poisson's ratios.Combined with the high-gradient belts of S-wave velocity,locking of faults,historical seismic gaps and long elapsed times of large earthquakes,we propose that these two segments of the Lijiang—Xiaojinhe fault are seismogenic environments with moderate to strong earthquakes and might have high seismic hazard potential in the near future.
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