A systematic analysis of correlation-based seismic location methods

Abstract

Waveform-based seismic location methods can reliably and automatically image weak seismic sources, such as microseismic events and microtremors. Besides the classical diffraction stacking operator which is based on the one-way traveltime, correlation-based imaging methods are another subcategory of waveform-based methods using differential traveltime. In this work, we systematically analyse the existing correlation-based methods and propose a novel hybrid correlation stacking method, which belongs to waveform-based relative location methods. The double differential traveltime from an event pair (i.e. a master event and a target event) to a receiver pair is used to stack the corresponding double correlation waveforms in this new approach. We generalize the correlation-based methods using a unified formula by describing cross-correlation stacking with beamforming. A thorough analysis of these imaging operators using synthetic and field data examples reveals their different characteristics of imaging resolution and level of redundancy, and a moderate level of redundancy can ensure both the accuracy and stability of correlation-based imaging methods, while an extremely high or low level of redundancy will hinder their performance in locating weak seismic events. The examples also demonstrate the potential disadvantage of using multiple phases with inaccurate velocity models for waveform-based location methods.