A minor 3.6-magnitude earthquake rattled the San Francisco Bay Area on Sunday morning near Alamo, California, with aftershocks reported afterward. U.S. Geological Survey data places the shaking as “weak” on the Modified Mercalli scale, though the quake may hav
At 8:37 a.m. Pacific time on Sunday, a 3.6-magnitude earthquake struck about 1 mile southwest of Alamo, California.
On the map released with the event, the shake intensity is shown only where the shaking is 3 or greater. U.S. Geological Survey defines that level as “weak,” but the same note warns the earthquake may have been felt outside the areas shown.
As seismologists review what they can detect and measure, the earthquake’s reported magnitude may change. Additional data collected about the quake may also lead U.S. Geological Survey scientists to update the shake-severity map.
After the first jolt, additional quakes were reported in the same area. These are typically aftershocks—small readjustments along the portion of a fault that slipped during the initial earthquake.
Aftershocks can arrive days, weeks, or even years later. They can be equal to or larger than the initial earthquake’s magnitude, and they can continue to affect places that may already be damaged.
The reporting around the event is tied to a timeline that uses Pacific time. The shake data on the map is as of Sunday, June 7 at 11:42 a.m. Eastern. The aftershocks data is as of Sunday, June 7 at 12:35 p.m. Eastern.
The mapped shaking categories are based on the Modified Mercalli Intensity scale. When aftershock data is available, the maps and charts include earthquakes within 100 miles and seven days of the initial quake.
The figures on the map draw from U.S. Geological Survey data for the epicenter, aftershocks, and shake intensity. Population density used on the mapping comes from LandScan via Oak Ridge National Laboratory.
San Francisco Bay Area earthquake 3.6 magnitude Alamo California aftershocks U.S. Geological Survey Modified Mercalli Intensity fault slip seismic map