Overview
- The U.S. Geological Survey recorded a magnitude 3.6 earthquake near Angwin at 2:30 p.m. Tuesday and a magnitude 2.6 event three minutes later, both at a shallow depth of about 3.9 miles.
- Residents in nearby towns such as St. Helena reported short, sharp shaking and there were no initial reports of damage or injuries.
- Seismologists have not yet identified which local fault produced the tremors, with the West Napa Fault Zone and the Concord-Green Valley Fault Zone both in the general area.
- Experts note shallow quakes transmit stronger surface shaking than deeper ones, which helps explain why the modest-magnitude event was felt, and they assess the odds it is a foreshock to a larger quake as low.
- The USGS provided the official location and magnitudes and investigators will continue analyzing data to determine the fault source and monitor for any further events that could prompt local inspections or advisories.