Geothermal Pumping and Induced Seismicity in California Geothermal Fields

Deborah A. Weiser, & Lucile M. Jones

Published April 2014, SCEC Contribution #2049

Induced earthquakes have been recognized for decades and observed in New Zealand, Switzerland, the US and elsewhere. Many factors can induce seismicity, including changes in pore pressure, temperature, volume, and chemistry. When fractured rock is injected with fluid, the effective normal stress and coefficient of friction are lowered and the rock is brought closer to failure. In this study, we examine the relationship between seismicity and geothermal pumping. We have obtained monthly injection and production data from the CA Department of Conservation for the Salton Sea Geothermal Field, Brawley Geothermal Field, and other California geothermal fields. We compare the temporal distribution of injection, production, fluid volume change (injection volume - production volume), and seismicity to determine if there are changes in the pumping rates that correspond to changes in seismicity rates. We observe a qualitative correlation between times of maximum fluid volume change and high seismicity levels, in particular, contemporaneous with the 2005 Obsidian Butte earthquake swarm. We also examine how changes in injection and production rates affect the Gutenberg-Richter b-value, earthquake depth, and focal mechanisms.

Weiser, D. A., & Jones, L. M. (2014, 4). Geothermal Pumping and Induced Seismicity in California Geothermal Fields. Presentation at 2014 SSA Annual Meeting.