A METHOD FOR IMPROVING THE DETERMINATION OF EARTHQUAKE HYPOCENTERS

In this paper, a hypocenter location method in the space domain is described. The major features of this method are: (1) it separates estimations of focal depth and origin time from estimations of epicenter location corrections; (2) in improving the epicenter location, the arrival time differences between double stations suggested by Romney and improved by Zeng Rong-sheng are used to lead to the least-squares condition, the normal equation are linear and the condition number is very low, so we obtain a fast and exact epicenter location almost independent of the velocity structure; (3) in determining the focal depth and origin time, the slope of arrival-time curve is used to estimate the focal depth and the time intercept of arrival time curve is found to estimate the origin time. Through testing and using this method, we find it is more valuable for the case needing more exact hypocenter location but understanding little about the structure of the district .The five industrial explosions Occurred in Sichuan province are used for testing the method and the results are good. Then, we have improved the fifty earthquake hypocentqrs occurred for last years. We have found: the modified epicenters are more closer to the faults; the travel-time residuals are decreased; a gradual increase in focal depth is shown from northeast to southwest along Longmen mountain faults.