Abstract

Multiplet-clustering analysis is a method for precise determination of microseismic event locations and is used to identify subsurface fractures and fracture networks. A multiplet is a group of microseismic events with very similar waveforms, despite different origin times, and it is likely the expression of stress release on the same structure. The relative source locations of similar events can be determined with high resolution and accuracy by using the moving-window cross-spectrum analysis technique. Deduced seismic clusters, called multiplet clusters, are indicative of seismically activated structures, and the orientations of these structures can be estimated using the seismic clusters even though the absolute locations of the multiplet clusters cannot themselves be determined. We examine methods of determining the relative locations of multiplet clusters and introduce the concept of clustering analysis. The clustering analysis method is used to estimate the relative location of multiplet clusters by detecting phase differences between similar stacked events. We describe the procedure for multiplet-clustering analysis, estimate relative locations of multiplet clusters, and apply the method to induced microseismic data from the Soultz Hot Dry Rock field, France. We show that a fracture network can be delineated through multiplet-clustering analysis, whereas it is difficult to identify detailed structures on the basis of source locations estimated by the joint hypocenter determination method.

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