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Primary source of quake detection, review, and public risk communication
San Ramon's earthquake swarm won't quit—even for Christmas. A magnitude 3.1 rattled the Tri-Valley on Christmas Eve morning, the latest tremor in a relentless cluster that has now delivered more than 300 earthquakes since early November. The biggest jolts came in a chaotic 24-hour stretch: a 4.0 on Friday evening, then a 3.9 on Saturday night, each followed by smaller aftershocks.
Updated Dec 25, 2025
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