In this paper, we retrieved relative source time functions (RSTF) and estimated thesource parameters for microearthquakes (M= -1.9 to -2.6) induced by hydraulic injectionat Fenton Hill, New Mexico, using an empirical Green's function (EGF) method.Seismic waveform of a small event in seismic doublets or multiplets (Gelle and Meuller,1980), defined as co-located events with similar focal mechanisms, within a hydraulicfracture zone, is treated as the EGF and is deconvolved from that of a larger event in the doublets or multiplets to retrieve the relative source time function. Time domain analysis of the RSTFs reveals the source complexity of the induced microearthquakes. Theazimuthal variation of the RSTF indicates that the rupture propagates to the northwest,which is consistent with the growth direction of the hydraulic fracture zone determinedby Li and Cheng (1995) with a seismicity temporal-spatial distribution pattern. Thesource duration of the induced events ranges from 2 to 8 ms and the source radii areestimated to be 4 to 12 meters. Values of stress drops are from 1 to 19 bars. Significantvariation of the stress drops may reflect the heterogeneity of the stress field in thehydraulic fracture zone and its vicinity and indicate that the stress field heterogeneityextends down to a few meters.
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