A complete microseismic event catalog with accurate source parameters can lead to a more thorough understanding of the temporal and spatial variation of stress during hydraulic fracturing operations. We detect, locate, and characterize repeating microseismic events by determining their source parameters such as magnitude, stress drop, and rupture size, and analyze the continuous microseismic data recorded by one borehole array during a hydraulic injection process. With an existing microseismic event catalog, we first re-calculate accurate moment magnitude and stress drop using estimated source spectra for all events. In addition, we detect and locate smaller events that show only clear S-wave arrivals using a template-matching and waveform cross-correlation technique to identify repeating microseismic activities. We obtain the template waveforms by stacking similar waveforms from repeating microseismic families. Among the ~1300 re-computed events, the moment magnitude calculated from the P- and S-waves spectra analysis ranges between Mw −1.5 and −3.5. These events are located within a 700m by 200m area as much as 250m deep. Our results indicate a fault radius on the order of one to six meters and fault slip between 10−5 to 10−3 cm around the fracturing region. In addition, using a matching-filter technique, we detect and locate low signal-to-noise ratio events that we consider repeating microseismic events. Our observations indicate that most repeating families occur at later times in shallower layers. Also, we observe a strong magnitude dependence of the stress drop, with larger magnitude events exhibiting significantly greater stress drops than smaller ones, in contrast to tectonic events in California or Japan. Our estimations of source parameters provide a key to a more in-depth understanding of the relationship between hydraulic fracturing and microseismic activity.

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