Joint Study Of Source Parameters Of Small To Moderate Earthquake

Accurate source parameters (moment, depth, strike, dip and rake of fault planes)are important for understanding seismotectonics and ground motion simulation. ForM5.5-6.5 earthquakes, they can be recorded at local, regional and teleseismic distanceswith sufficiently high signal noise ratio, and they can be well approximated with pointsources. We developed a joint algorithm in inverting both depth and focal mechanismwith local/regional and teleseismic waveforms. First we employed the Cut and Paste(CAP) method developed by Zhao and Helmberger in modeling mechanism and depthwith local waveforms. Then we add teleseismic data to constrain the source parameterswithvariableweightbetweenlocalandteleseismicwaveforms. Inthisstudy,westudiedseveral events with different fault geometries。Firstly, Different sensitivities associated with local and teleseismic datasets wereanalysed by performing a CAP inversion for the focal depth and mechanism of twoMs6.6 earthquakes of 11th Jul, 2004 and 07th Apr,2005, using local and teleseismicdatasets respectively. Then we performed a joint inversion(CAPjoint)by taking theadvantage of local and teleseismic datasets. A robust result of focal mechanism canbe obtained by fully exploiting the amplitude ratio content of the different data sets,including amplitude ratio between Pnl and Surface wave, Rayleigh and Love wave, Pand SH wave. The CAPjoint method can achieve a stable and reliable focal depth, withutilization of depth phase such as sPL, sPg, sPn of near-field waveform and sP, pP offar-field waveform and free surface reflection wave of SH. Due to high-quality broad-band waveform data of Hi-Climb project, we employed CAP method to determined thefocal depth and mechanism of part of aftershocks of the two Zhongba earthquake. Theresults showed that the focal mechanisms of the main shock and aftershocks are basi-cally normal events with North-South strike, partof which with a slight slip component,which represent a East-West stretch action and consistent with regional tectonic struc-ture. The sequence with focal depth from 3km to 14km, is due to the brittle fracture ofseismogenic zone with earthquake nucleation in the upper crust.The co-seismic deformation field in the line of sight (LOS) associated with thesetwomainshockswasobtainedfromSARimagesrecordedbytheEuropeanSpaceAgency's (ESA) C-Band ENVISAT. We used the interferometric pair 20040317 and 20040908to obtain the co-seismic deformation of 11th July, 2004 main event. Correspondingly, the deformation of 7th April, 2005 main shock was resolved using acquisitions from thepair20040317and20040908. Weutilizedasensitivity-basediterativemethod(Wangetal. 2008) to derive the slip distribution from the InSAR data. The fault dimension of the11th July, 2004 was 16km×16km, in the along-strike and down-dip directions, respec-tively, while the fault dimension of 7th April, 2005 extended 27 km along-strike and18 km in the down-dip direction. Moveover, to better understand the rupture zone, werelocated parts of the aftershock. The results from seismological and geodetic methodshow satisfactory consistency , with adjacent rupture zone non-overlapped.we performed a joint inversion for the focal depth and mechanism of Ms6.1 Pan-zhihua-Huili, Sichuan, earthquakeofAug30, 2008, bytakingtheadvantageoflocalandteleseismic datasets. We also carry out a waveform fitting method to investigate the fo-cal depth of ML≥4.0 earthquake sequence of Panzhihua-Huili earthquake, using sPLphase, which is insensitive to epicentral distance, but sensitive with the focal depth.The focal mechanism solution of the main shock shows that the earthquake sequenceis associated with a left lateral strike-slip faulting with a small thrust component. Oneof two nodal planes of focal mechanism solution with the geometrical configuration:strikein194°,dipat78°andarakeof12°,isconsistentwiththeYuanMou-LuZhijiangfault.The focal depth of the main shock derived from sPL phase shows substantial con-sistency with that obtained from joint CAP method with the best fitting depth 11km andthe depths of the ML≥4.0 aftershock mainly flock around the vicinities of the depth11km and 16km,matching the focal depths distribution of historical seismic events ofwest Sichuan. We inferred that Panzhihua-Huili earthquake sequence is due to brittlefracture of seismogenic zone with earthquake nucleation in the upper crust. We alsosuggest that YuanMou-LuZhijiang fault is seismogenic fault and seimic focus locates atthe approximate vertical part which may prolongate to the middle crust.In the sixth chapter, by the analysis of surface wave, the 9th Oct, 2007 Katanningearthquake shows an ultra shallow seismicity, with focal depth lower than 1km. Weobtained a simple one-dimensional layered S velocity model based on the dispersioncurve of surface wave and consequently obtained a relatively robust focal mechanismwith strike in 54.4°,dip at 44.0°and a rake of 131°. Furthermore, we forward mod-eled the co-seismic deformation based on the One-dimension layered S wave velocitymodel. The predicted and observed LOS deformation of four cross-section across seis-mic zone show great consistency with the focal depth of 0.35km. The moment mag-nitude obtained from seismological method with Mw4.5 differed from which deducedfrom InSAR data with Mw4.7, probably due to a rapid post-seismic deformation, which represents that a 36.9% moment of the InSAR detection is due to post-seismic defor-mation. This may associate with rheological characteristics of the ultra shallow part ofweathered cap or laterite layer.