Application Of VELEST In Earthquake Location

The Yunnan region is located in the southwest of China.Its geological structure is complex,and the internal activities of the earth are frequent and intense.Not only that,but there are many staggered fault structures in the Yunnan region.This special geological background makes the Yunnan region become a rich source of research on the internal activities of the Earth in China.One of the regions.In 2003,two strong earthquakes occurred successively in the Dayao region of Yunnan—the 6.2-magnitude earthquake on July 23 and the 6.1-magnitude earthquake on October 16.The Dayao area in Yunnan is located within the Central Yunnan structural block,with the Chenghai fault to the west,the Lijiang-Xiaojinhe fault to the north,and the Nanhua-Chuxiong fault and the Hongge fault and other fault belts in the east and south,respectively.There is no obvious fracture in the earthquake area.This paper integrates the earthquake catalog data of Dayao area in 2003 and uses VELEST program to calibrate the velocity models of PREM,WWJ,and YNU three prior models with different parameter conditions,and uses the minimum one-dimensional velocity structure model obtained under each condition.Double-difference positioning.While comparing the effects of different velocity models on the accuracy of the double-difference location,the earthquake activity in the Dayao area of Yunnan and the connection between the two earthquakes are discussed.The following conclusions have been obtained:1.Double-difference positioning cannot completely eliminate the effect of velocity structure blur on seismic inversion accuracy.When the theoretical velocity model and the actual model differ greatly,there is a certain deviation in the distribution of the source,and there is a phenomenon that the depth of the source diverges to a deeper region.2.The VELEST program can obtain the station correction result of the same prior information while correcting the speed structure,and theaccurate model and station information obtained are conducive to the improvement of the accuracy of the seismic positioning.VELEST has a unique role in the correction of velocity models in areas with complex structural backgrounds.3.In the Dayao area,the two earthquake sequences are in a linear strip-like distribution in NW-SE.The two earthquakes are controlled by the same seismogenic fault and show a unilateral rupture trend.4.Concealed faults may exist in Dayao region.Due to the problem of underground internal tectonic environment,the existing means did not find obvious faults in this area,and it needed to resort to artificial seismic exploration and other means.In the two regions with underground depths of 4-14 km and 22-44 km in this area,activities on the Earth are active.5.In 2003,after two strong earthquakes in Dayao,and after the6.2-magnitude earthquake ruptured to NW,the energy in the SE direction was not completely released.The remaining energy was accumulated as a basis to a certain degree,and a subsequent 6.1-magnitude earthquake was formed.