Study Of Source Parameters And Rupture Directivity Of Moderate Earthquakes Based On Waveform Inversion

Determination of source parameter of earthquake is the basic topic of seismology. Focal mechanism shows regional stress state and focal depth reflects rheology feature of medium, rupture directivity can be used to confirm the fault on which the earthquake occurs.In chapter1, we first introduce inversion methods of source parameters.In chapter2,we invert for focal mechanisms of Xinyuan Ms6.6earthquake on June30th,2012with the "Cut and Paste"(CAP) method (CAPloc、CAPtel、 CAPjoint), using broadband localseismic data from Xinjiang seismological network and broadband teleseismic data from GSN seismological network. The result shows that the best double-couple solutions of this Ms6.6event is293°,62°,152°for strike,dip,rake, respectively. The other nodal plane is37°,66°,30°with19km focal depth and6.3moment magnitude. We also relocated earthquake sequences with double-difference location algorithm (HypoDD) to get accurate information of spatial distribution of aftershocks, and the result shows that the earthquake sequences show a NWW trend. So, we concluded that the nodal plane:293°/62°/152°is possible to be the physical rupture surface. The Xinyuan Ms6.6earthquake is very likely to be caused by the movement of Kashi river fault, a right-lateral thrust strike slip fault, resulting from the N-S compressional stress field in Tianshan region.In chapter3, we adopt the CAP method to develop a system, which can rapidly determine the focal mechanisms automatically in the East-Tianshan area.The Green’s functions are computed utilizing the Frequency-Wavenumber method and the layered velocity structure is based on the1-D velocity model. To reduce the computational time of the procedure, Green’s functions are already computed in advance at a1km interval from20up to500km along epicentral distance and a1km interval from1down to50km along source depth, and stored in a library. To test the effectiveness of the procedure, we study10earthquakes with magnitude greater than5, which occurred within the survey region between2006and2013. Focal mechanisms and moment magnitudes of all the events are comparable to the results from the Global Centroid-Moment-Tensor (CMT) Project, indicating that the system has certain feasibility.In chapter4, we develope a techniqueto determine the rupture planevia measuring the spatial difference between the centroid location and hypocenter, and apply the approach to the2008Yingjiang Ms6.0earthquake. We also discuss the influence of the error of absolute earthquake location and origin time, as well as the inaccuracy of velocity model.