M2.7 Earthquake 9 km NE of Alum Rock, CA — September 23, 2023
2023-09-23 22:02:35 UTC (2023-09-23) · approx. 2:02 PM UTC-8 local
Felt by 37 people across nearby locations.
On September 23, 2023 at 22:02 UTC, a magnitude 2.7 shallow crustal earthquake struck 9 km NE of Alum Rock, CA, at a depth of 11.1 km and coordinates 37.4305°, -121.7723°. This earthquake was detected by 129 seismic stations with excellent location accuracy and was assigned a USGS significance rating of 123, placing it among routine seismic activity.
Physical scale: An earthquake of magnitude 2.7 releases seismic energy equivalent to roughly 153 kg of TNT. Empirical fault-scaling laws (Wells & Coppersmith, 1994) estimate the subsurface rupture length at approximately 42 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 37 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
-121.7723°E
Technical Information
Nearby Earthquakes (Last 7 Days)
Common Questions
How strong was the magnitude 2.7 earthquake near Alum Rock, CA?
The magnitude 2.7 earthquake that struck 9 km NE of Alum Rock, CA on September 23, 2023 at 22:02 UTC had a depth of 11.1 km. For context, this was a minor earthquake typically detected only by instruments.
Where did the earthquake occur?
The earthquake epicenter was located at 37.4305°, -121.7723°, which is 9 km NE of Alum Rock, CA. View all earthquakes in California.
Were there aftershocks?
Aftershock activity is monitored continuously by the USGS. Aftershock sequences from magnitude 2.7 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 2.7 event is significantly smaller than that historical record.
Actions
Authoritative source: USGS event page (event ID: nc73940946). All scientific values on this page are sourced verbatim from the USGS feed.
Cite this page: EarthquakeTracker.org. (2023, September 23, 2023). M2.7 Earthquake 9 km NE of Alum Rock, CA — September 23, 2023. Retrieved December 2, 2023 from https://www.earthquaketracker.org/earthquakes/event/nc73940946/