Back to today’s briefing

Story perspectives

California Hit by 9-Earthquake Swarm, Experts Weigh In

12/20/2025

35 6 Full Breakdown

Summary

Story summary

A swarm of nine or more earthquakes struck southeast of San Ramon, California, on December 19, 2025, with magnitudes from 2.5 to 4.0.
The strongest quake, magnitude 4.0, struck at 7:56 p.m. at 6.2 miles deep.
Residents felt the tremors as the swarm produced over 150 earthquakes in the past month.
US Geological Survey experts say swarms do not necessarily predict larger quakes and reflect fluid interactions with faults.

1 of 1

Story summary

A swarm of nine or more earthquakes struck southeast of San Ramon, California, on December 19, 2025, with magnitudes from 2.5 to 4.0.
The strongest quake, magnitude 4.0, struck at 7:56 p.m. at 6.2 miles deep.
Residents felt the tremors as the swarm produced over 150 earthquakes in the past month.
US Geological Survey experts say swarms do not necessarily predict larger quakes and reflect fluid interactions with faults.