| After an earthquake, for ordinary people, the first concern is the occurrence time, epicenter, magnitude of the earthquake, known as "The three elements of earthquake". Magnitude size reflects the size of the energy released by an earthquake. According to the different methods, the magnitude is generally including body wave magnitude, surface wave magnitude, moment magnitude, the determination of magnitude is relatively mature in seismology. The other two parameters of "the three elements of earthquake":the origin time of earthquake, epicenter and earthquake focal depth, that is to say the spatial and temporal parameters of seismic source. The location of hypocenter is equal to solve the focal spatial and temporal parameters of an earthquake or an earthquake sequence. It is a classical problem in seismic inversion. The accuracy of the earthquake spatial and temporal parameters is the basis of the earth science to study seismic structure, preparation process and understanding of an earthquake. Therefore, earthquake location has been one of the most basic problems in seismology.Earthquake location methods including absolute location and relative location method are mainly developed from a classical absolute location method put forward by Geiger. Modern earthquake precise location method usually use the double difference relocation method, which is a relative location method. The method is particularly suitable for the earthquake sequences that hypocenter position concentrated, and one of the most important characteristics of reservoir induced earthquake is the earthquake cluster distribution. we have used accurate location and analysis combined the double difference relocation method and waveform cross-correlation of seismic sequence of Xiaowan reservoir.We relocated the earthquakes which are ML≥1.5occurred before and after the impoundment of Xiaowan reservoir. After analyzing the relocated epicenter and focal depth and frequency of the earthquakes, the results are as follows: 1. One of the main factors influencing the result of earthquake location accuracy is the time-delay of the phase, we can obtain more accurate time-delay by using waveform cross-correlation technique which calculate the cross-correlation function which the phases of two earthquake waveforms to the same stations. At the same time the structure of crustal velocity in Yunnan area detected by people of former times, localization based on velocity model within Xiaowan reservoir area, further improve the location accuracy.2. The result of relocation used the double difference relocation method in the earthquakes of Xiaowan reservoir from2005to2012shows that:after relocation, the epicenter of Xiaowan reservoir’s earthquakes are more centralized in the area of the two river basin, focal depth relative to the original depth distribution is more continuous. The result of relocation which use double difference relocation method with waveform cross-correlation has a significant improvement by the relocation process and error analysis,3. By comparing the activity frequency of10clusters of earthquakes in the reservoir area, network records the epicenter distribution location, depth distribution of image before and after impoundment, we can get a preliminary judge that the cluster number1,5,10of earthquakes which occurred after impoundment are reservoir-induced earthquakes, and the others are basically background earthquakes of Xiaowan reservoir area.4. We can have a conclusion that the earthquakes are reservoir-induced earthquakes which occurred in the reservoir area after July of2010with seismic depth-frequency, depth-time as well as the seismic activity with the change of reservoir water level analysis, and the reservoir-induced earthquakes began to occur after the reservoir water-level reaching1150m in altitude, and the seismic activity in Heihui River Basin and the process of impoundment are closely correlative, the earthquakes which occurred in Heihui River Basin are typical reservoir-induced earthquakes. |
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