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

Abstract

We report on the development of an automated Local Waveform Correlation Event Detection System (LWCEDS) and its application to the New Mexico Tech Seismic Network. LWCEDS is an adaptation of a global system, WCEDS, a matched filtering algorithm for global Comprehensive Test Ban Treaty (CTBT) monitoring applications developed at Sandia National Laboratories and New Mexico Tech. Although the current CTBT monitoring system is based on teleseismic phase detection, effort is being placed on research to highlight specific areas of the globe for which local and regional seismic networks could be employed. An automated waveform correlation regional location system could also serve as a rapid alert and automated location system by providing magnitude and hypocenter information within a few minutes of the occurrence of a hazardous earthquake. In the LWCEDS algorithm, processed waveforms are correlated with theoretical travel-time envelopes, and a grid search is performed to identify the space-time solutions that yield the highest correlations. High correlation indicates that an event has occurred and that a good approximation to the correct origin time and hypocenter has been determined; explicit phase identification is not required. To avoid the large computational expense of calculating a complete correlation for each grid point, we use a laterally homogeneous velocity model and reformulate the problem into a single matrix multiplication and matrix assessment for each time step. LWCEDS has been successfully tested on a suite of local and regional seismic events selected to span the range of expected event quality. Preliminary results from our sparse 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. Similar results were obtained during an on-line experiment conducted to generate daily bulletins during the time period from 3 December 1996 through 7 January 1997. Data from 156 triggers were processed, including 33 teleseisms, 102 regional events (includes explosions), and 21 local earthquakes. Results from this expanded test set are encouraging but reveal the need for a method to mask or flag various electronic and telemetry spikes.

Preliminary Analysis of Source Physics Experiment Explosion‐Triggered Microseismicity Using the Back‐Projection Method

“…Stacking raw amplitudes from distant receivers alone creates issues with amplitude, phase, and polarity, particularly with uncorrelated signals. Correcting these issues requires preprocessing techniques that transforms continuous raw amplitudes to envelopes (Withers et al, 1998(Withers et al, , 1999, continuous short-term-average long-term-average ratios (STA/LTA) (e.g., Joswig, 1990;Vanderkulk et al, 1965), and continuous kurtosis (e.g., Baillard et al, 2014;Ross & Ben-Zion, 2014), all which rectify the waveforms before stacking. Artifacts in BP images can be caused by incorrect velocity models used in CF time-shifting and stacking or using P-wave travel-times to shift and stack CF containing mostly S-waves.…”

Multiband array detection and location of seismic sources recorded by dense seismic networks

“…The transformed signal is then converted into time-series of 3-D spatial images representing an energy or likelihood function, through delay-and-sum (or migration) techniques, using arrival time prediction combined with a grid search strategy. Early examples of this second class of methods involve CFs based on short-term over long-term average (STA/LTA) in the context of earthquake location at regional and local scales (Withers et al 1999), and the Source Scanning Algorithm, initially developed by Kao & Shan (2004 in the context of tectonic tremors location, extended by Liao et al (2012) to earthquake aftershocks.…”