A Case Study In Focal Mechanism And Rupture Directivity Of The 2009 Yaoan Ms6.0 Earthquake

Source parameters is quantitative expression of seismic source characteristics according to the analysis of seismic data.lt includes the basic parameters of the earthquake epicenter location (longitude and latitude), focal depth, seismic moment and magnitude of earthquakes or earthquake energy and seismic mechanism solutions and focal parameters.Accurate determination of source parameters on the cause of the earthquake research has important significance.Earthquake rupture directivity is an important parameter to describe the earthquake rupture process, through the earthquake rupture direction, can determine the focal mechanism solutions of two nodal plane which actual physical fault rupture,thus better understanding seismogenic mechanism.Determination of seismogenic faults, is the base of the research on the seismogenic process and the disaster mechanism, can also provide key information for post disaster reconstruction and long-term economic and social plans.The method of solving the focal mechanism is varied, but it mainly includes the following, namely, using the P wave first to seek the fault plane solution, the P wave and the S wave amplitude ratio, and the waveform inversion method. First motion of P wave method is simple and quick, but obtained from the waveform data in seismic information less, so the method for P wave first motion clarity and dense network of have a high requirements, and only in a large number of station data and uniform distribution of stations in order to get reliable results.P wave and S wave amplitude ratio method can improve the seismic source parameters, so as to reduce the uncertainty of the fault parameters, but it is limited by the station distribution, which is influenced by the medium. Body waveform inversion method has low dependence on velocity structure , so the result is relatively stable, the method through suitable for earthquake, teleseismic inversion, but the amplitude of the waveform is relatively weak, the signal-to-noise ratio is low using the methods of inversion of focal mechanism solutions more difficult. Seismic surface wave with high signal-to-noise ratio and large amplitude, can be used for effective inversion of seismic focal mechanism solutions.But the resolution of focal depth and the time function is low ,and the surface wave velocity dependent on the propagation path of the structure.lt can be found that the use of body wave and surface wave inversion of seismic source mechanism solutions may bring a large error, the integrated use of body wave and surface wave information to carry out the inversion of focal mechanism solutions is necessary.Zhao and helmberger in 1994 proposed cap (cut and paste) method. the method has been improved. The method is a representative of the full waveform inversion method has, along with the improvement of the cap method of continuous development. Now it has been widely used in the inversion of focal mechanism and source depth.In this paper,we carried out data collection and analysis in Yaoan and Dayao area of yunnan province. Including the earthquakes more than mag 6 during 2000, the regional geological structure and earthquake faults around.Using the focal mechanism of Yaoan Ms6.0 earthquake CAP inversion solutions in 2009, the results show that the earthquake to strike slip type earthquake, the two group nodal plane parameters were:Section 1 295° /76 ° /-174 ° ; section 2 203° /84° /-14° and the results with gcmt gives results consistent, the focal depth of 7km, and the result is close to the results given by GCMT.Focal depth is 7.6km,which is closed to the depth obtained in the study of Qin Shuanglong.In this paper, the method is based on the relative centroid to measure the rupture directivity. The results indicate that the fault plane heading for the 294 degree fault plane is a real seismic surface.And the study of different reference earthquakes indicate that the different reference earthquakes do not affect the determination of rupture direction. The inaccuracy of the mainshock epicenter location and the time earthquake occurs, mechanism solution difference.The results show that he above factors have no influence on the rupture direction, but have a certain influence on the calculated fracture length.And the verification shows that using the stations of less than 30 degrees to the difference of mechanism solutions to inverse mainshock mechanism solution generate less error than using all stations.