The Application Of Wavelet Transform And Earthquake Location In Zipingpu Reservoir Area

Around the12May2008Wenchuan earthquake, the Zipingpu SeismographNetwork and Dense Seismograph Network (constructed by Institute of Geology,China Earthquake Administration) have completely recorded the Wenchuan8.0earthquake and its aftershocks. As both the networks are very close to the epicenterthe data recorded are extremely valuable. Based on these high-accuracy seismic data,this thesis carried out wavelet transform analysis and earthquake relocation for theZipingpu Reservoir area.The wavelet transform is a new time-frequency analysis method, which wasdeveloped from the end of the20th century. It can reflect the characteristic changeswith time in the frequency domain, and is suitable for analysis of non-stationaryseismic signals. This work used the Matlab to write and debug the wavelet transformprogram, and calculated wavelet packet transform spectra of31earthquake events(magnitude2.0) recorded by the Zipingpu Seismograph Network, then it identifiedand classified the types of seismic ruptures. After a brief discussion and summary ofseveral common phase identification methods, this work combined the wavelettransform method and seismic wave polarization characteristics to carry out theautomatic picking of seismic phases for part data of the network.After the Wenchuan earthquake, seismologists have relocated the Wenchuan greatearthquake and its aftershocks, yielding different focal depths (6-19km) of the mainshock. Such a big uncertainty cannot meet the needs of the following study. This workused the double-difference hypocenter locating method to relocate the Wenchuanmain shock and6478small events recorded by the Zipingpu Seismograph Network.In this method, the impact of ray path velocity model imprecise on locations results isreduced, and the events which cannot be paired are removed. Finally, this processingobtained4307events as precise results with EW average error0.062km, NS average error0.063km, and UD average error0.612km.This work has made the following conclusions:1. Through the relocations of earthquakes recorded in by the ZipingpuSeismograph Network, the focal depth of Wenchuan main shock is determinedto be about7km. And most aftershocks are located in a depth range2-12km..2. The analysis of wavelet packet transform shows that there are three event typesof single rupturing, repeated rupturing and double rupturing in the ZipingpuReservoir area. The results show that the wavelet packet transform is a usefultool to identify types of earthquakes.