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Seismic activity at The Geysers

One of the tidbits picked up on our recent trip to The Geysers was about the seismic activity around the resource. Since it is a geothermal resource, one of the things an exploration team looks for is seismic activity as it is a primary indicator of resource.

It was a surprise to me (but really shouldn’t have been) that the seismic activity in the region has increased both in frequency of activity and magnitude since the field has been in production. Logically, one would expect that if you’re taking huge amounts of mass from underground that there would be some impact, at the very least, subsidence. This isn’t to say there are huge cataclysmic quakes happening, the quakes tend to be small and frequent.

Click the map to visit the USGS for more detail.

As you can see from the USGS quake map above, there are 52 quakes in the past week, the cluster of events near the left, top of the map is in The Geysers region. The magnitude of these quakes range from 1-3 typically, though a 4.4 was registered in the Calpine leasehold in the past few years. Curiously, the activity has increased with the injection measures taken to replace mass extracted from the production wells. Since the reservoir is a series of fractures in a confined space, this may be from overloading certain areas of the reservoir rather than a more even distribution of the injected fluid across the fissures.

Nevertheless, a very interesting side effect of the geothermal activity in The Geysers region.

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