The Rapid And Precise Location Methods Of Continental Earthquakes

With the popularizing of digital seismic observation network and the development of electronic communication network, determining earthquake location rapidly and releasing information about the earthquake quickly have become the urgent requirements. Therefore, it is the direction of long term efforts to improve the accuracy of the earthquake location, especially focal depth. Rapid determination of location can provide pivotal guidance for earthquake early warning and dibaster assistance. And precise location can provide important information of continental seismicity, which is helpful to understand internal stress environment of focal area and mechanism of the earthquake to provide important references for earthquake regularity, disaster evaluation and trend judgment. It is mostly based on the observational data of mobile stations near the epicenter to study rapid and precise location method. For instance, mobie station near Suining earthquake is used to study single station location method and focal depth determination. For another example, mobile stations monitoring aftershocks of Anqing quake are used to study precise location method with clock error. In addition, the aftershock sequences of two earthquake dublets such as Dayao earthquakes and Zhongba earthquake have been location precisely to study whether strong shock’s fracture zone can occur another sizable rupture.Accurate positions by using traditional multiple stations method are obtained dependent of correct crustal structure and dense and uniform seismic network. However, many continental earthquake, especially small and moderate earthquake, do not have perfect stations’distribution and reliable three dimensional structure, which resulted in great system errors of rapid earthquake information report, particularly focal depth. As the gradatim intensiving of global and regional seismic network, in most places sigle station has a good cover, then using single three-component seismic records to determine earthquake position information has become the direction of pratical significance. By using the frequences and phases of digital broadband seismic waves, this paper has located some M2earthquake sequences shocked in Suining with single station method.Accurate locations of aftershocks are helpful to understanding ruptured process of main shock. The arrival-time differences between Sg and Pg by temporary seismic array installed after the January19th,2011Anqing quake were used to reconstruct the travel-time data of Pg and Sg, in order to suppress the impact of instrumental clock error. Furthermore, more accurate locations of main shock and aftershock sequences were obtained by using master event and double difference method. An algorithm was proposed to estimate the range of clock error. More reliable depth distribution of aftershocks was obtained via analysing sPL, a depth phase at near epicentral distance. This study shows that the Anqing earthquake happened near Susong-Zongyang fault zone, and aftershocks were concentrated in the depth range about5km underground nearly horizontally, spreading in the shape of a thin slab which is around1.5kilometer long,1.0kilometer wide and a thickness of0.3kilometer. Moreover, the sequence spreaded to the north-east with the time. It is suggested that the influence of clock error can be eliminated by S-P arrival-time difference method effectively, which can provide reliable location results for moderate and minor earthquakes, as well as aftershocks.After the shock, has strain energy of the rupture zone already been released enough? Or has an other earthquake with the like magnitude shocked again inside the plane of the first fracture? These questions are the important issues concerning earthquake doublets. It is to be found that aftershock zones have been expanded, although aftershock zones have hardly any overlapped in both depth direction and horizontal direction by using the relocation method of double difference (hypoDD) to2003Dayao two earthquake sequences. And the July21Quake to the October16Quake is from the North West. In addition, it is also to be found that the strike directions of two rupture zones might vary slightly analyzing initial motion of P wave, coinciding with the relocated results of aftershock zones. These results imply that the two Dayao earthquakes, which are near enough, may occur inside the different segments of a fault system. It can be said that these two rupture zones have not overlapped.