Location Estimation Using Regional Array Data

摘要

A location estimation procedure for locating regional seismic events with a network including arrays and single element seismometers is described. The method incorporates back azimuth estimates, arrival time data and associated uncertainties into a generalized-inverse location estimate. The formulation allows the use of both a priori and a posteriori information about data uncertainties to compute confidence ellipsoids for the location estimates. This is important for obtaining realistic confidence ellipsoids for solutions based on few data. It provides for a refinement of the confidence ellipsoid calculations as experience accumulates for events in a particular area, and this is an important element of our regional location estimation procedure. Small arrays like NORESS in Norway provide accurate estimates for the back azimuth of regional phases. These azimuth data provide a strong constraint on the location for events detected by a small number of stations, including at least one array. The strength of the constraint depends on the geometry, and in some situations azimuth data are as important as arrival time data. Synthetic examples illustrating this are given for a network including two arrays. Comparing one array and two array locations and their confidence ellipses with these independent locations provides a preliminary validation of our estimates of the (signal-dependent) a priori arrival-time and azimuth variances and demonstrates the effectiveness of our location procedure for a sparse network of regional arrays.