M3.9 Earthquake 1km NE of San Ramon, CA — November 17, 2021
2021-11-17 19:43:43 UTC (2021-11-17) · approx. 11:43 AM UTC-8 local
Felt by 4,732 people across a wide area. Maximum shaking intensity MMI 4.6 (moderate).
On November 17, 2021 at 19:43 UTC, a magnitude 3.9 shallow crustal earthquake struck 1km NE of San Ramon, CA, at a depth of 10.3 km and coordinates 37.7892°, -121.9688°. The earthquake was reported felt by 4,732 peopleacross a wide area, with a maximum shaking intensity of Modified Mercalli Intensity (MMI) 4.6 (moderate). This earthquake was detected by 221 seismic stations with excellent location accuracy and was assigned a USGS significance rating of 649, making it a moderate-impact event.
Physical scale: An earthquake of magnitude 3.9 releases seismic energy equivalent to roughly 9.3 metric tons of TNT. Empirical fault-scaling laws (Wells & Coppersmith, 1994) estimate the subsurface rupture length at approximately 278 m — a useful intuition for the size of the slip patch on the fault.
The epicenter is located in California, a region characterized by the San Andreas transform fault system, where the Pacific and North American plates slide past each other at roughly 46 mm per year. The nearest mapped fault system is the San Andreas Fault. View all earthquakes in California.
Learn more: San Andreas Fault · Magnitude scale · Aftershock sequences
What the Shaking Felt Like
At MMI 4.6 (moderate), people in the most strongly affected areas would have experienced: Mild shaking, similar to a passing truck. Hanging objects swing. Glasses and dishes may rattle. Not commonly felt outdoors.
ShakeMap — predicted shaking intensity
Modeled ground-motion intensity contoured on the Modified Mercalli scale (MMI). Computed by the USGS from the moment-tensor solution and regional ground-motion prediction equations.
Source: U.S. Geological Survey ShakeMap. View interactive ShakeMap on USGS
Did You Feel It? — community-reported shaking
Aggregated felt-report intensity from 4,732 citizen responses to the USGS Did You Feel It? system. Each colored zone represents the average MMI from reports in that area.
Source: U.S. Geological Survey Did You Feel It?. View on USGS · submit your own report
Earthquake Details
-121.9688°E
Technical Information
Nearby Earthquakes (Last 7 Days)
Common Questions
How strong was the magnitude 3.9 earthquake near San Ramon, CA?
The magnitude 3.9 earthquake that struck 1km NE of San Ramon, CA on November 17, 2021 at 19:43 UTC had a depth of 10.3 km. It was felt by 4,732 people with maximum shaking intensity of MMI 4.6 (moderate). For context, this was a minor earthquake typically detected only by instruments.
Where did the earthquake occur?
The earthquake epicenter was located at 37.7892°, -121.9688°, which is 1km NE of San Ramon, CA. View all earthquakes in California.
Were there aftershocks?
Aftershock activity is monitored continuously by the USGS. Aftershock sequences from magnitude 3.9 earthquakes can continue for several days and gradually diminish over time.
Has California had earthquakes this big before?
The largest recorded earthquake in California was the M7.9 Fort Tejon earthquake of January 9, 1857. Today's magnitude 3.9 event is significantly smaller than that historical record.
Actions
Authoritative source: USGS event page (event ID: nc73654060). All scientific values on this page are sourced verbatim from the USGS feed.
Cite this page: EarthquakeTracker.org. (2021, November 17, 2021). M3.9 Earthquake 1km NE of San Ramon, CA — November 17, 2021. Retrieved April 2, 2026 from https://www.earthquaketracker.org/earthquakes/event/nc73654060/