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An oblique Google Earth map of the San Francisco Bay area, looking north from the Santa Cruz mountains. Major cities, active tectonic faults, and the location of the San Ramon earthquake swarm are highlighted. The Clear Lake Volcanic Field, Mount Shasta, and the Berkeley Hills volcanics are also annotated to show that the San Ramon earthquake swarm is not happening near any active volcanoes.
Map of the January-February 2026 San Ramon earthquake swarm, Bay area faults, and volcanic areas
Map of the January-February 2026 San Ramon earthquake swarm, Bay area faults, and volcanic areas
Map of the January-February 2026 San Ramon earthquake swarm, Bay area faults, and volcanic areas

This oblique Google Earth map shows the location of the 2026 San Ramon earthquake swarm, along with notable faults in the San Francisco Bay area and the nearest volcanic areas to the swarm. Google Earth image modified by J. Ball, USGS.

A simplified set of plots of earthquake sequences, with magnitude on the vertical and time on the horizontal axis. In the top plot, dots show earthquake magnitude starting off large and getting smaller and less frequent over time. On the bottom plot, earthquake magnitudes and times don't follow any particular pattern but happen in bursts.
Types of earthquake sequences
Types of earthquake sequences
Types of earthquake sequences

These simplified plots of earthquake magnitude versus time show the differences between tectonic earthquake sequences and magmatic earthquake swarms. Figure by Alicia Hotovec-Ellis, USGS.

These simplified plots of earthquake magnitude versus time show the differences between tectonic earthquake sequences and magmatic earthquake swarms. Figure by Alicia Hotovec-Ellis, USGS.

This shaded relief map shows the Long Valley Caldera, Lake Crowley, and the town of Mammoth Lakes. Highway 395 cuts diagonally across the caldera from northwest to southeast. In the center of the map, a label shows the location of GPS station KRAC/KRAK.
Location of GPS (GNSS) station KRAC/KRAK in the Long Valley Caldera
Location of GPS (GNSS) station KRAC/KRAK in the Long Valley Caldera
Location of GPS (GNSS) station KRAC/KRAK in the Long Valley Caldera

The location of GPS station KRAC and its predecessor KRAK, slightly north of the center of deflation in Long Valley. USGS figure by Josh Crozier and Alicia Hotovec-Ellis.

A line graph shows the average vertical position of a GPS station over time in centimeters, starting in 1995. The graph starts at 0, rises to 10 cm in 2000, peaks at 15 dcm in 2004, then begins climbing again in 2012. It reaches a peak of 22 cm in 2022, labeled with an arrow and "onset of decrease in seismicity", then decreases to 15 cm by 2025. Small blue dots scattered above and below the line show individual measurements from the station.
The average of individual measurements from GPS station KRAC/KRAK in the Long Valley Caldera, 1995-2025
The average of individual measurements from GPS station KRAC/KRAK in the Long Valley Caldera, 1995-2025
The average of individual measurements from GPS station KRAC/KRAK in the Long Valley Caldera, 1995-2025

The average of individual measurements from GPS station KRAC/KRAK shows about 6 cm of ground subsidence since 2021. The multi-year deflation stands out above smaller fluctuations caused by noise in the data and seasonal water infiltration (the peaks and troughs in the dots for individual measurements). USGS figure by Josh Crozier and Alicia Hotovec-Ellis.

The average of individual measurements from GPS station KRAC/KRAK shows about 6 cm of ground subsidence since 2021. The multi-year deflation stands out above smaller fluctuations caused by noise in the data and seasonal water infiltration (the peaks and troughs in the dots for individual measurements). USGS figure by Josh Crozier and Alicia Hotovec-Ellis.

This map shows the Mono Lake - Long Valley region and part of the Sierra Nevada to the south. The landscape is shown in shades of gray while earthquakes are depicted with orange dots scaled according to the earthquake's magnitude. Black lines indicate where seismic monitoring boxes are drawn around Mono Lake, the Long Valley Caldera, the Sierra Nevada, and Mammoth Mountain.
Map of the Long Valley region with earthquakes from 2025
Map of the Long Valley region with earthquakes from 2025
Map of the Long Valley region with earthquakes from 2025

Locations of earthquakes of at least magnitude 1.0 in 2025 and the outlines of the boxes CalVO uses to count earthquakes around Long Valley. Only 6 earthquakes were located inside the Long Valley Caldera box. (Earthquake location data from Northern California Seismic Network.) Figure by Alicia Hotovec-Ellis, USGS. 

Locations of earthquakes of at least magnitude 1.0 in 2025 and the outlines of the boxes CalVO uses to count earthquakes around Long Valley. Only 6 earthquakes were located inside the Long Valley Caldera box. (Earthquake location data from Northern California Seismic Network.) Figure by Alicia Hotovec-Ellis, USGS. 

Two line graphs show the yearly number of earthquakes over since 1980 in the Long Valley Caldera and the Sierra Nevada south of the caldera. Several annotations write out the numbers of earthquakes in a few years, including 2025.
Earthquakes per year from 1980-2026 in Long Valley and the nearby Sierra Nevada
Earthquakes per year from 1980-2026 in Long Valley and the nearby Sierra Nevada
Earthquakes per year from 1980-2026 in Long Valley and the nearby Sierra Nevada

Graphs of the number of earthquakes located each year since 1980 in the Long Valley Caldera and nearby Sierra Block monitoring boxes. Note that the number of earthquakes on the left shown on a logarithmic scale, which means they increase an order of magnitude with each "step." Figure by Alicia Hotovec-Ellis, USGS.

Graphs of the number of earthquakes located each year since 1980 in the Long Valley Caldera and nearby Sierra Block monitoring boxes. Note that the number of earthquakes on the left shown on a logarithmic scale, which means they increase an order of magnitude with each "step." Figure by Alicia Hotovec-Ellis, USGS.

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