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The Calaveras Fault is famous for earthquake swarms - clusters of small earthquakes that rattle the Tri-Valley area (San Ramon, Dublin, Pleasanton) every few years. It's one of the most seismically active faults in the Bay Area.
113 earthquakes have been recorded near the Calaveras Fault in the past 7 days. This elevated activity is typical of swarm behavior in the San Ramon area.
The Calaveras Fault is a major strike-slip fault that extends 75 miles from Hollister in the south through the East Bay hills to the Danville/San Ramon area in the north. It's part of the San Andreas Fault system and branches off from the Hayward Fault near Fremont.
What makes the Calaveras Fault unique is its tendency to produce earthquake swarms - sequences of many small earthquakes occurring over days or weeks without a clear mainshock. The San Ramon area is particularly prone to these swarms, experiencing noticeable activity every few years.
The fault moves at about 15mm per year in the creeping southern section near Hollister, but the northern section through San Ramon is locked and releases stress through periodic swarms and occasional larger earthquakes.
The San Ramon/Danville area is one of the most swarm-prone areas in California. Here are some of the most notable swarms in recent years:
Major swarm that rattled residents with hundreds of small earthquakes over two weeks. Largest was M3.6.
Swarm centered under the Tassajara area. Many earthquakes felt by residents.
Notable swarm with a M4.5 mainshock felt across the entire Bay Area.
Sustained swarm activity in the typical San Ramon cluster area.
Moderate swarm with dozens of felt earthquakes over several days.
| City | Population | Distance | Risk |
|---|---|---|---|
| San Ramon | 84K | On fault | Very High |
| Danville | 44K | On fault | Very High |
| Dublin | 72K | 1 mi | Very High |
| Pleasanton | 79K | 2 mi | High |
| Livermore | 90K | 5 mi | High |
| Alamo | 15K | 2 mi | High |
| Walnut Creek | 70K | 4 mi | Moderate |
| Morgan Hill | 46K | On fault | Very High |
| Hollister | 42K | On fault | Very High |
| Fault | Length | Max Potential | Behavior |
|---|---|---|---|
| Calaveras | 75 mi | M7.0 | Frequent swarms |
| Hayward | 62 mi | M7.0 | Locked, overdue |
| San Andreas | 800 mi | M8.0+ | Locked segments |
Stay informed about earthquake swarms in the Tri-Valley.