Generalized Beamforming, Phase Association and Threshold Monitoring using a Global Seismic Network

Abstract

Generalized beamforming is an approach to multi-channel processing of data recorded by a network of seismic stations which represents an extension of the delay-and-sum beam-forming traditionally applied in array processing. A number of geographical beam-steering points are defined, and for each beam a set of time-aligned traces derived from the network of stations are processed together so as to extract, for each step in time, a set of features corresponding to that particular beam. Applying this approach to the various regional and global network configurations, we demonstrate its usefulness for associating phases detected at individual stations and originating from the same event. The method differs from traditional phase association techniques as it provides an exhaustive search algorithm that is computationally efficient and well suited for parallel processing. We also address the problem of using a network to continuously monitor the seismic noise field. The purpose here is to determine to what extent interfering events affect the monitoring of events within a target region. In this regard, we show that one can obtain, at a given confidence level, a continuous assessment of the upper limit of magnitudes of seismic events in the target region that would go undetected by such a network.