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Automated epicenter locations from a quadripartite array

Joint ESSA-U of H Tsunami Research Effort Environmental Science Services AdministrationUNIVERSITY OF HAWAII, HONOLULUHAWAII INSTITUTE OF GEOPHYSICS

Abstract

A quadripartite seismic array has been installed on the island of Oahu, Hawaii, to supply additional data for the Tsunami Warning System of the USCGS. The nuclear explosion LONGSHOT on October 29, 1965, on Amchitka Island served in calibrating the epicenter location system. A moving cross-correlation determined the P wave time delays between the various station pairs. Time delays were then used in a least-squares method to obtain azimuth and emergence angles. The emergence angle is used with the Jeffreys-Bullen travel-time curve to obtain the distance to the source. The emergence angles obtained by using the observed station-pair time delays should be corrected to the emergence angles obtained by using the station-pair time delays as computed from the Jeffreys-Bullen travel-time curve. This comparison will then compensate for the anomalies of the Pacific area. With the values for azimuth and distance, one can then arrive at an approximate epicenter location for earthquakes of normal depth. This method can be used for those situations which require an epicenter location within minutes after the earthquake has been recorded. Methods developed here are designed for an on-line computer.