M3.9 Earthquake 6km NE of Petrolia, CA — December 20, 2021
2021-12-20 21:53:46 UTC (2021-12-20) · approx. 1:53 PM UTC-8 local
On December 20, 2021 at 21:53 UTC, a magnitude 3.9 shallow crustal earthquake struck 6km NE of Petrolia, CA, at a depth of 26.9 km and coordinates 40.3585°, -124.2258°. The earthquake was reported felt by 1 personacross nearby locations, with a maximum shaking intensity of Modified Mercalli Intensity (MMI) 3.2 (light).
Physical scale: An earthquake of magnitude 3.9 releases seismic energy equivalent to roughly 12 metric tons of TNT. Empirical fault-scaling laws (Wells & Coppersmith, 1994) estimate the subsurface rupture length at approximately 310 m — a useful intuition for the size of the slip patch on the fault.
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 1 citizen response 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
-124.2258°E
Technical Information
Nearby Earthquakes (Last 7 Days)
Common Questions
How strong was the magnitude 3.9 earthquake near Petrolia, CA?
The magnitude 3.9 earthquake that struck 6km NE of Petrolia, CA on December 20, 2021 at 21:53 UTC had a depth of 26.9 km. It was felt by 1 person with maximum shaking intensity of MMI 3.2 (light). For context, this was a minor earthquake typically detected only by instruments.
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.
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Understanding This Data
Magnitude 3.9 earthquakes are typically only recorded by instruments.
Authoritative source: USGS event page (event ID: nc73666511). All scientific values on this page are sourced verbatim from the USGS feed.
Cite this page: EarthquakeTracker.org. (2021, December 20, 2021). M3.9 Earthquake 6km NE of Petrolia, CA — December 20, 2021. Retrieved March 1, 2022 from https://www.earthquaketracker.org/earthquakes/event/nc73666511/