| Abstract | Induced seismicity occurs both in conventional oil/gas
fields due to production and water injection and in
unconventional oil/gas fields due to hydraulic fracturing.
Source mechanisms of these induced earthquakes are of
great importance for understanding their causes and the
physics of the seismic processes in reservoirs. Previous
research on the analysis of induced seismic events assumed
a double-couple (DC) source mechanism. However, recent
studies have shown a non-negligible percentage of a nondouble-
couple (non-DC) component of source moment
tensor in hydraulic fracturing events (Rutledge et al. 2003,
Šílený et al., 2009; Warpinski and Du, 2010; Song and
Toksöz, 2011). In this study, we determined the full
moment tensor of a large number of earthquakes from an
oil/gas field. The seismicity of the field and source
mechanisms of events using DC assumption have been
studied extensively (Sarkar, 2008; Li et al., 2011, 2012).
Song and Toksöz (2011) developed a full waveform based
complete moment tensor inversion method to investigate
induced events. In this study, we inverted and compared the
source mechanisms of induced events with and without DC
constraints. We investigated the accuracy of moment
tensors on number of stations, azimuthal distribution, and
signal to noise ratio. We conducted tests with synthetic data
to validate the method before the application to the real
data. Our results show that the double-couple component of
the MT is determined most accurately. The accuracy of
isotropic and CLVD components depend on data quality
and station coverage. |
