TY  - JOUR
ID  - epos1685
UR  - http://doi.org/10.1002/2014JB011385
IS  - 11
A1  - Martinez-Garzon, Patricia
A1  - Kwiatek, Grzegorz
A1  - Sone, Hiroki
A1  - Bohnhoff, Marco
A1  - Dresen, Georg
A1  - Hartline, Craig
Y1  - 2014/11//
N2  - The spatiotemporal, kinematic, and source characteristics of induced seismicity occurring at
different fluid injection rates are investigated to determine the predominant physical mechanisms responsible
for induced seismicity at the northwestern part of The Geysers geothermal field, California. We analyze a
relocated hypocenter catalog from a seismicity cluster where significant variations of the stress tensor orientation
were previously observed to correlate with injection rates. We find that these stress tensor orientation changes
may be related to increased pore pressure and the corresponding changes in poroelastic stresses at reservoir
depth. Seismic events during peak injections tend to occur at greater distances from the injection well,
preferentially trending parallel to themaximum horizontal stress direction. In contrast, at lower injection rates the
seismicity tends to align in a different direction which suggests the presence of a local fault. During peak
injection intervals, the relative contribution of strike-slip faulting mechanisms increases. Furthermore, increases
in fluid injection rates also coincide with a decrease in b values. Our observations suggest that regardless of the
injection stage, most of the induced seismicity results from thermal fracturing of the reservoir rock. However,
during peak injection intervals, the increase in pore pressure may likewise be responsible for the induced
seismicity. By estimating the thermal and hydraulic diffusivities of the reservoir, we confirm that the characteristic
diffusion length for pore pressure is much greater than the corresponding length scale for temperature and also
more consistent with the spatial extent of seismicity observed during different injection rates.
PB  - John Wiley & Sons
JF  - Journal of Geophysical Research: Solid Earth
VL  - 119
SN  - 2169-9313
TI  - Spatiotemporal changes, faulting regimes, and source parameters of induced seismicity: A case study from The Geysers geothermal field
SP  - 8378
AV  - none
EP  - 8396
ER  -