Source Parameters Of Small To Moderate Earthquakes In The Yunnan And Its Adjacent Area (2000-2007)

Yunnan province is located in the east edge of collision between the India and Eurasia plates in the mainland China, affected by the tectonic stress field in the north east India collision, intense crustal activity, which leads to a tectonic process in the region is very complicated, seismic activity with the characteristics of high frequency, high magnitude and wide distribution. The seismic events in Yunnan area there is a certain rule, and the earthquake disaster is one of the important reasons for the loss of people’s lives and property and social property in Yunnan. Focal mechanism solution can provide a large number of important seismic information, such as the spatial direction of origin time, focal location, focal depth, seismic moment (direct measurement of seismic energy), magnitude, and seismic moment tensor. The determination of the seismic source parameters:seismic moment, focal mechanism solution and depth can draw the seismogenic fault quickly, and serve for earthquake disaster assessment and earthquake emergency, stable regional source parameters also can effectively serve the earthquake early warning systems.Different from traditional by method of P wave initial motion information and amplitude ratio information to calculate the focal mechanism solution, in this study, seismic waveform inversion was used to determine focal mechanism solution of regional ML≥3.0 earthquakes (a total of 2202) in the Yunnan and its adjacent area from 2000 to 2007. After Artificial screening, remove the fitting result is bad, finally, the focal mechanism solutions of 766 earthquakes are obtained. In the course of study, we taken the two groups of amplitude parameters to remove the instrument response, at the same time, the three one dimensional velocity models is used to calculate the Green’s function.The purpose of this paper is to study a stable regional focal mechanism solution of Yunnan area from 2000 to 2007, the results can provide data for regional stress and fault. The 766 earthquake focal mechanism solutions obtained are mostly strike-slip type earthquake, conform to the characteristics of tectonic stress field in Yunnan region, explained to the reliability of waveform fitting method. The larger of the magnitude, the better of fitting in waveform fitting method. Using waveform fitting method to calculate focal mechanism solution of aftershock sequence are related to the occurrence of main time interval, the size of the earthquake magnitude, and frequency of seismic events during this period. We were able to successfully determine 33 source parameters down to Ml= 3.0, significantly lower than the moment tensor solution threshold of about Mw 5.0 for the Global CMT, the advantage of using waveform fitting method to calculate the focal mechanism is more obvious.