M3.1 Earthquake 5km S of Ridgemark, CA — August 21, 2021
2021-08-21 19:54:46 UTC (2021-08-21) · approx. 11:54 AM UTC-8 local
Felt by 17 people across nearby locations.
On August 21, 2021 at 19:54 UTC, a magnitude 3.1 shallow crustal earthquake struck 5km S of Ridgemark, CA, at a depth of 9.3 km and coordinates 36.7720°, -121.3740°. This earthquake was detected by 73 seismic stations with excellent location accuracy and was assigned a USGS significance rating of 153, placing it among routine seismic activity.
Physical scale: An earthquake of magnitude 3.1 releases seismic energy equivalent to roughly 674 kg of TNT. Empirical fault-scaling laws (Wells & Coppersmith, 1994) estimate the subsurface rupture length at approximately 83 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
Did You Feel It? — community-reported shaking
Aggregated felt-report intensity from 17 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
-121.3740°E
Technical Information
Nearby Earthquakes (Last 7 Days)
Common Questions
How strong was the magnitude 3.1 earthquake near Ridgemark, CA?
The magnitude 3.1 earthquake that struck 5km S of Ridgemark, CA on August 21, 2021 at 19:54 UTC had a depth of 9.3 km. For context, this was a minor earthquake typically detected only by instruments.
Where did the earthquake occur?
The earthquake epicenter was located at 36.7720°, -121.3740°, which is 5km S of Ridgemark, CA. View all earthquakes in California.
Were there aftershocks?
Aftershock activity is monitored continuously by the USGS. Aftershock sequences from magnitude 3.1 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 3.1 event is significantly smaller than that historical record.
Actions
Authoritative source: USGS event page (event ID: nc73613006). All scientific values on this page are sourced verbatim from the USGS feed.
Cite this page: EarthquakeTracker.org. (2021, August 21, 2021). M3.1 Earthquake 5km S of Ridgemark, CA — August 21, 2021. Retrieved November 2, 2021 from https://www.earthquaketracker.org/earthquakes/event/nc73613006/