M4.0 Earthquake 12 km NW of Stanley, Idaho — October 2, 2021
2021-10-02 23:47:42 UTC (2021-10-02) · approx. 3:47 PM UTC-8 local
Felt by 19 people across nearby locations. Maximum shaking intensity MMI 4.4 (moderate).
On October 2, 2021 at 23:47 UTC, a magnitude 4.0 shallow crustal earthquake struck 12 km NW of Stanley, Idaho, at a depth of 7.0 km and coordinates 44.2936°, -115.0512°. The earthquake was reported felt by 19 peopleacross nearby locations, with a maximum shaking intensity of Modified Mercalli Intensity (MMI) 4.4 (moderate). The USGS PAGER system issued a green alert level for this event, indicating no significant casualties or damage expected. The nearest populated place is Challis (population 1,081).
Physical scale: An earthquake of magnitude 4.0 releases seismic energy equivalent to roughly 15 metric tons of TNT. Empirical fault-scaling laws (Wells & Coppersmith, 1994) estimate the subsurface rupture length at approximately 347 m — a useful intuition for the size of the slip patch on the fault.
The epicenter is located in Idaho, a region characterized by the track of the Yellowstone hotspot and the Centennial Tectonic Belt, producing both volcanic and tectonic seismicity. View all earthquakes in Idaho.
Learn more: Magnitude scale · Aftershock sequences
Nearest Populated Places
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 19 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
Population exposure (USGS PAGER)
Estimated population that experienced each level of shaking. Based on the USGS PAGER rapid impact assessment, which combines ShakeMap output with global population grids.
| Shaking intensity (MMI) | Description | Population exposed |
|---|---|---|
| MMI 3 | weak | 118 |
| MMI 4 | light | 309 |
Earthquake Details
-115.0512°E
Technical Information
Nearby Earthquakes (Last 7 Days)
Common Questions
How strong was the magnitude 4.0 earthquake near Stanley, Idaho?
The magnitude 4.0 earthquake that struck 12 km NW of Stanley, Idaho on October 2, 2021 at 23:47 UTC had a depth of 7.0 km. It was felt by 19 people with maximum shaking intensity of MMI 4.4 (moderate). For context, this was a light earthquake commonly felt near the epicenter.
Where did the earthquake occur?
The earthquake epicenter was located at 44.2936°, -115.0512°, which is 12 km NW of Stanley, Idaho. The nearest populated place is Challis (population 1,081). View all earthquakes in Idaho.
Were there aftershocks?
Aftershock activity is monitored continuously by the USGS. Aftershock sequences from magnitude 4.0 earthquakes can continue for several days and gradually diminish over time.
Has Idaho had earthquakes this big before?
The largest recorded earthquake in Idaho was the M7.3 Borah Peak earthquake of October 28, 1983. Today's magnitude 4.0 event is significantly smaller than that historical record.
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Location
Authoritative source: USGS event page (event ID: us6000fr7b). All scientific values on this page are sourced verbatim from the USGS feed.
Cite this page: EarthquakeTracker.org. (2021, October 2, 2021). M4.0 Earthquake 12 km NW of Stanley, Idaho — October 2, 2021. Retrieved December 10, 2021 from https://www.earthquaketracker.org/earthquakes/event/us6000fr7b/