Imaging of seismic events : The role of imaging conditions, acquisition geometry and source mechanisms

Abstract

Localization of seismic events can provide us valuable information about structures activated by tectonic stresses, geothermal or volcanic activity, reservoir stimulation, and other subsurface activities. In the last few years automatic stacking-based localization methods, which do not require any picking, have proved to be reliable localization tools. Localization results obtained by such techniques are influenced by various circumstances. Influence of three key factors is studied in this work such as imaging conditions, acquisition geometry and source mechanisms. First, a commonly used imaging condition is discussed and alternatives are introduced. Then, I illustrate their advantages, limitations and sensitivity to velocity uncertainties.

Secondly, influence of acquisition geometry on localization results is examined. I illustrate impact of regularly and irregularly distributed receivers. Ways of acquisition footprint reduction are discussed.

Furthermore, localization of events with different source mechanisms is illustrated. Events with a double-couple source mechanism represent a challenge for stacking-based localization techniques due to waveform differences among receivers. An alternative stacking-based approach, especially suitable for the localization of double-couple dominant events, is introduced. As the majority of seismic events can be best characterized by a combination of explosive, double-couple (DC) and compensated linear vector dipole (CLVD) components, localization of such sources is also illustrated.

Finally, an application to field data from Southern California is presented. Despite the sparse and irregular receiver distribution, localization result obtained by a stacking-based localization technique deviates less than 1% of the maximum receiver offset to the location yielded by California Earthquake Data Center using a method requiring picking of phases.