The ability to detect small microearthquakes and identify their P and S phase arrivals is akey issue in hydrofracture downhole monitoring because of the low signal-to-noise ratios.We apply an array-based waveform correlation approach (matched filter) to improve thedetectability of small magnitude events with mechanisms and locations similar to anearby master event. After detecting the weak events, we use a transformed spectrogrammethod to identify the phase arrivals. We have tested the technique on a downholemonitoring dataset of the microseismic events induced by hydraulic fracturing. We showthat, for this case, one event with a signal-to-noise ratio around 6dB, which is barelydetectable 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-stackedcorrelation traces. The transformed spectrogram analysis of the detected events improvesP and S phase picking.
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