Abstract
A procedure to locate seismic events uses the value of the crosscorrelation
coefficient between waveforms of different events. First, an empirical
relation between spatial event separation and maximum crosscorrelation
coefficient is established for a subset of a priori located reference
events. Then this relation is used to determine the hypocenters of
an increasing number of events by a grid-search strategy. Measured
arrival-time differences between S- and P-waves also constrain the
location. Although the reference events are located by a standard
method using the arrival-time measurements at three or more receivers,
the correlation-based location requires only one receiver. The method
has been applied to microseismic data recorded at a single borehole
sensor during the 2004/05 injection experiment at the Continental
Deep Drilling Site (KTB) in Germany. With the approach, significantly
more weak seismic events were located, compared to the number of
events recorded by a near-surface receiver array and by inversion
of arrival times. The proposed location method is particularly well
suited to locate small-magnitude earthquakes within dense event clouds
when too few arrival-time observations for part of the events are
available and standard location methods fail. These conditions are
frequently met in the case of microseismic monitoring of geothermal
or enhanced oil recovery experiments.
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