Abstract
The ability to detect small microearthquakes and identify their P-
and S-phase arrivals is a key issue in hydrofracture downhole monitoring
because of the low signal-to-noise ratios (S/N). An array-based waveform
correlation approach (matched filter) is applied to improve the detectability
of small magnitude events with mechanisms and locations similar to
a nearby master event. After detecting the weak events, a transformed
spectrogram method is used to identify the phase arrivals. The technique
has been tested on a downhole monitoring data set of the microseismic
events induced by hydraulic fracturing. It is shown that, for this
case, one event with a S/N around 6 dB, which is barely detectable
using an array-stacked short-time average/long-time average (STA/LTA)
detector under a reasonable false alarm rate, is readily detected
on the array-stacked correlation traces. The transformed spectrogram
analysis of the detected events improves P- and S-phase picking.
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