[PDF][PDF] Characterizing Microseismicity at the Newberry Volcano Geothermal Site using PageRank

AC Aguiar, SC Myers - 2016 - osti.gov
AC Aguiar, SC Myers
2016osti.gov
ABSTRACT The Newberry Volcano, within the Deschutes National Forest in Oregon, has
been designated as a candidate site for the Department of Energy's Frontier Observatory for
Research in Geothermal Energy (FORGE) program. This site was stimulated using high-
pressure fluid injection during the fall of 2012, which generated several hundred
microseismic events. Exploring the spatial and temporal development of microseismicity is
key to understanding how subsurface stimulation modifies stress, fractures rock, and …
Abstract
The Newberry Volcano, within the Deschutes National Forest in Oregon, has been designated as a candidate site for the Department of Energy’s Frontier Observatory for Research in Geothermal Energy (FORGE) program. This site was stimulated using high-pressure fluid injection during the fall of 2012, which generated several hundred microseismic events. Exploring the spatial and temporal development of microseismicity is key to understanding how subsurface stimulation modifies stress, fractures rock, and increases permeability. We analyze Newberry seismicity using both surface and borehole seismometers from the AltaRock and LLNL networks. For our analysis we adapt PageRank, Google’s initial search algorithm, to evaluate microseismicity during the 2012 stimulation. PageRank is a measure of connectivity between an instance (web-site, event, signal, etc.) and a collection of other instances, where higher ranking represents more connections. In our seismic application connectivity is measured by the cross correlation of 2 time windows recorded on a common seismic station and channel. Aguiar and Beroza (2014) used PageRank to detect low-frequency earthquakes, which are highly repetitive but difficult to detect. We expand on this application by using it to define signal-correlation topology for micro-earthquakes, including the identification of signals that are connected to the largest number of other signals. We then use this information to create signal families and compare PageRank families to the spatial and temporal proximity of associated earthquakes. Studying signal PageRank will potentially allow us to efficiently group earthquakes with similar physical characteristics, such as focal mechanisms and stress drop. Our ultimate goal is to determine whether changes in the state of stress and/or changes in the generation of subsurface fracture networks can be detected using PageRank topology.
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