Analysis of Seismic Activity in the Middle Part of the North-South Seismic Belt——Joint Study on Deep Seismic Sounding Profile and Seismicity Parameters

摘要

Using the rich deep seismic sounding data recorded in the middle part of the NorthSouth Seismic Belt in China,the horizontal and vertical profiles are constructed to obtain the seismic velocity structure,analyze the seismic distribution and calculate the seismic energy and the thickness of the seismogenic layer at the same time.On this basis,the seismicity parameters are calculated using the earthquake catalogue of the study area for the past 40 years,and the relationship between the b-value distribution and the velocity structure is analyzed.The results show an uneven b-value distribution in the study area and a segmented feature along the Longmenshan fault zone.Most of the earthquakes occur in the transition zone anomalies from the positive to the negative.In addition,the thickness of the crust drops from ~60 km to ~48 km from the Southeastern to the Northeastern Qinghai-Tibetan Plateau,but the thickness of the seismogenic layer increases gradually.It is speculated that the crustal composition of the Northeastern margin contains more felsic materials and has relatively stronger seismic activities than the Southeastern Qinghai-Tibetan Plateau,possibly associated with the subduction and compression of the Indian Ocean Plate.