Relocation Of Earthquakes Using Double Difference Algorithm And Its Application For Seismological Routine Location

With the increased density of the seismic monitoring network of China and theimplementation of earthquake science data sharing project and the development ofmodern technology for earthquake location, such as double difference earthquakelocation algorithm, which provide objective conditions for the precision focal locationdetermination. The research work of this dissertation is developed under thosecircumstances.The major content for this paper consists of three parts:The first part uses double difference algorithm (DDA) to relocate the earthquakesoccurred in China since 1985. According to the distribution of seismic activity andavailability of record for earthquakes, we consider Capital Circle, Xinjiang area andChuandian area with high frequency seismic activity and dense distribution of stationas subjects of scientific research. On the base of the present data for earthquake, inconjunction with arrival time from different origins, which increase in number ofrecord for earthquakes and enlarge the density of station distribution for those threeareas, we relocate the earthquakes from three regions by using DDA, analyzing therelated result, collecting the events with precision parameters for earthquake derivedfrom DDA as fundamental reference events, the results are summarized as follows:(1) The distribution of earthquakes of Capital Circle, Xinjiang area andChuandian area have great changes before and after relocating, earthquakes distributeover a considerable extent before relocating, we obtain a clearer view of seismicitydistribution after relocating, the image of relocated epicenters are consistent withmajor fault systems expressed at the surface, approaching the fracture zone, it showsspatial characteristics of relocation are in close correlation with the tectonic structure.The number of relocate earthquake are less than before relocating, the relocation foraverage RMS residual of three regions are reduced remarkably, the depth measuringrange are in coincidence with research results for those areas from predecessors. Theresults in many aspects show the DDA is an available method for seismic locationwith high precision determination.(2) There are significant differences between those three areas in the number ofrelocation events and average RMS residual. The number of relocation events accountfor 60.5%, 43.3 %, 62.6% of all events respectively, the average RMS residual forCapital Circle area has the lowest value, followed by Chuandian area, Xinjiang area'sis relatively larger. The prime reason for the difference is to be affected by stationsdistribution. The practical experience shows the relocation results are more precisewith more events and stations used in processing of relocation by DDA.(3) This paper provide a term of fundamental reference event, explaining thesignificance of it in the study of seismological science, we collect the relocation of8850 earthquakes derived from DDA with precision parameters as fundamentalreference events, these events have precision parameters of original time, latitude,longitude, focal depth, establishing a database for fundamental reference event thatwill be used in the study of seismological science by science research personnel. We attempt to apply DDA into the routine work of earthquake location in thesecond part. The results derive from seismological general work are revised throughmaking use of the DDA results. Practice has shown that not all of events derive theaccurate parameters for earthquakes from applying the DDA. We can obtain more fineresults with more events and stations in process of relocation by using DDA. Due toapplication of DDA requires strict condition, there exists some shortages whenapplying the DDA into the routne work of earthquake location, however, our researchwork is a successful exploration with good prospect to promote the use of modernmethod for earthquake location.The third part describes in detail the Winding-Number algorithm in topology anddata documentation required procedures. The geographical name of the Chinaearthquakes are determined by the Winding-Number algorithm, they are determined tothe level county and town. Query process is accurate, efficient and small error.According to the practical requirements of query procedure will be applied to theFlinn-Engdahl (F-E) regionalization scheme, The earthquakes occurred in china havebeen detailed geographical names, and better complied with the publicationrequirements of seismic observation report, with ease for the foundation research ofseismology.The Winding-Number algorithm with the following characteristics determinesthe geographical names of the China earthquakes:(1) The names of geographical location for earthquakes with high precisionretrieved by procedure are consistent with actual location of earthquakes.(2) According to different areas from the largest down to smallest to search thenames of geographical position for earthquakes until to output the name, to do so,which saves some time and speeds up the executive rate of procedure.(3) The error during retrieving derives chiefly from the digitizing process andsampling interval size for boundary line of China's Country-level Administration, inthis paper, sampling interval scale is five kilometer for border-regions, that is to say,the retrieval error is about five kilometer.