Study on Method of Further Improving Epicenter Locating Precision Based on Pg Onsets of Three Stations in Earthquake Warning System

Aiming at the phenomenon of the larger error and instability that exits in the epicenter location based on Pg onsets of three stations,combined with virtual seismic network of Shandong Province,we analyze the influence of the difference of regional velocity structure and geometric distribution of stations on locating precision of epicenter,and give the apparent velocity model of direct Pg wave to put forward the integrated solutions scheme on epicenter location based on Pg onsets of three stations.The epicenter location results of 1 555 earthquakes recorded by the virtual seismic network of Shandong Province from 2009 to 2013 indicates that the average error of epicenter location is 8.7 km by Pg onsets of three stations( compared with the epicenter location in network),which can improve the precision of epicenter location and deduce the probability of epicenter cannot be determined.