Characterizing Source Properties Of Historical Earthquakes Using Macro-Seismic Data

Characterizing seismic source properties using macro-seismic data has long been a 'classical' topic in seismology,as can be shown by the works from Shabalin(1973), Chen(1975),Koyama and Zheng(1991) and Panza et al(1991) to Sirovich(1996,1997), Molchan et al(2002,2004) and Fitzko et al(2005).Being a complicated problem,it deals with earthquake rupture,propagation of seismic waves in heterogeneous media, site effect of strong ground motion,destruction of buildings,determination of intensity,and plotting of isoseismals.In this thesis,balancing the models in use and the quality and availability of observation data,relatively simple models are used to retrieve source properties from isoseismals.To this end the KF-method proposed by Sirovich(1996,1997) was systematically analyzed and reproduced using MatLab. Considering the plotting of isoseiamals in China,taking the method of Chen(1975) as a reference,a rectangle seismic source was used,with the theoretical consideration that radiation directivity degenerating for high frequencies(Satoh,2002;Castro et al., 2006),to several earthquakes in China.The algorithm modified from KF-method can also act as a simplified version of ShakeMap.Collecting the intensity data of north China,conducting map-projection correction and sampling/digitalizing using MapInfo, programming using MatLab,and adding the 30"(about 1km resolution) topography data in the mapping,a user-oriented database was constructed,with 111 historical earthquakes in north China in the Ming and Qing Dynasty(1477～1911) and 52 earthquakes in north China in the late 20^th century(1966～2000).The database is indexed by time with detailed users guide.Using trail-and-error approach retrieve source parameters from isoseismal contours,an interactive program was written implementing the method of Chen(1975) and the modified KF-method.Discussion on the effect of focal depth,strike and dip on the plotting of isoseismals gives the estimate of the uncertainties of the source parameter retrieval.The program was applied in a testing mode to the 1668 Juxian-Tancheng earthquake,the 1679 Sanhe-Pinggu earthquake,the 1830 Cixian earthquake,the 1966 Xingtai earthquake, 1976 Tangshan earthquake,and the 2008 Wenchuan earthquake.