An automated local and regional seismic event detection and location system using waveform correlation

We report on the development of an automated Local Waveform. Correlation Ev ent Detection System (LWCEDS) and its application to the New Mexico Tech Se ismic Network. LWCEDS is,an adaptation of a global system, WCEDS, a matched filtering algorithm for global Comprehensive Test Ban Treaty (CTBT) monito ring applications developed at Sandia National Laboratories and New Mexico Tech. Although the current CTBT monitoring system is based on teleseismic p hase detection, effort is being placed on research to highlight specific ar eas of the globe for which local and regional seismic networks could be emp loyed. An automated waveform correlation regional location system could als o serve as a rapid alert and automated location system by providing magnitu de and hypocenter information within a few minutes of the occurrence of a h azardous earthquake. In the LWCEDS algorithm, processed waveforms are correlated with theoretica l travel-time envelopes, and a grid search is. performed to identify the sp ace-time solutions that yield the highest correlations. High correlation in dicates that an event has occurred and that a good approximation to the cor rect origin time and hypocenter has been determined; explicit phase identif ication is not required. To avoid the large computational expense of calcul ating la complete correlation for each grid point, we use a laterally homog eneous velocity model and reformulate the problem into a single matrix mult iplication and matrix assessment for each time step. LWCEDS has been succes sfully tested on a suite of local and regional seismic events selected to s pan the range of expected event quality. Preliminary results from our spars e network show typical epicentral errors of less than 3 km for local events and, with notable exceptions, to within 10 to 20 km for regional events. S imilar results were obtained during an on-line experiment conducted to gene rate daily bulletins during the time period from 3 December 1996 through 7 January 1997. Data from 156 triggers were processed, including 33 teleseism s, 102 regional events (includes explosions), and 21 local earthquakes. Res ults from this expanded test set are encouraging but reveal the need for a method to mask or flag various electronic and telemetry spikes.