Many geothermal power plants induce seismicity near injection wells when they are operating, but a small
but increasing number of them have been found to have seismicity induced near production wells by shutdowns
(shut-ins), presumably due to pore pressure and/or poroelastic stress increases. A very dense seismic array
deployed at about 1,300 sites by Microseismic, Inc. in 2016 at the San Emidio geothermal plant during a brief
(~1 day) shutdown located about 130 discrete events (microseismic events) using a back-projection method
during the shutdown. As part of a multi-institutional, multi-disciplinary project known as WHOLESCALE, a
dense array of 450 3-component nodal instruments was deployed in 2022 for about a month to record data before,
during, and after shutdown, covering part of the area of the 2016 array. I will discuss some of the key finding
from those two data sets. We compare in some detail the fault patches that were activated in 2016 versus 2022
compared to the fault model developed for San Emidio. We also pose a few questions of interest, some of which
we hope to answer eventually.
