| Together with a realistic velocity model and a well-designed seismic monitoring
system, the quality of arrival time measurements is one of the most important factors
to limit the uncertainty in the earthquake location problem. The accuracy of time
picks is generally increased by exloiting the waveform similarity. This allows to
calculate more precise differential arrival times which replace or improve the original
arrival time picks. Typically, the waveform data are processed either event-based or
receiver-based.
Here, we propose to combine the receiver- oriented and the event- oriented approaches to
optimize simultaneously arrival time picks for micro seismic events recorded by
multi-level borehole arrays. The method extends existing concepts by cross-linking
waveforms of different events in a multiplet recorded by closely spaced receivers, and the
increased interconnectivity of waveforms also increases the consistency of the arrival
time data. We apply the method to a hydraulic fracturing experiment, where micro
seismic data were recorded by two inclined borehole arrays consisting of 30 receivers.
It is shown that the picking accuracy is significantly improved compared to the
original picks and also compared to the adjusted picks obtained from single receiver
based processing. We also compare the improved event relocations with the original
locations. |