Why are there so many earthquakes in the Geysers area in Northern California?
The Geysers geothermal field is located in a tectonically active region of Northern California. The major seismic hazards in the region are from large earthquakes occurring along regional faults that are located miles away from the geothermal field, such as the San Andreas and Healdsburg-Rodgers Creek faults. However, activities associated with the withdrawal of steam for producing electric power cause or induce small quakes to occur in the field. These smaller quakes are frequently felt by those who work at the field and by nearby residents. Seismicity at The Geysers was poorly documented when power generation commenced in the 1960’s, but since 1975 high-quality seismic monitoring data has been available, and it has been demonstrated that increased steam production and fluid injection correlates positively with changes in earthquake activity. The level of seismicity has been fairly stable since the mid-1980s, even though power production has declined in the field with the depletion of
