quarry blast · reviewed by a seismologist
M 1.8md
Earthquake near Jamestown, CA
No earthquake was likely felt in Jamestown in the 24 hours to 9:27 pm PST (05:27 UTC). The last one was M 5.2, 192 km (119 mi) NE, at 1:17 am PDT on 1 May 2026, estimated intensity II (weak) in town; 1,875 felt reports to USGS. Every earthquake near Jamestown
No: USGS classifies this as a quarry blast, not an earthquake. A magnitude 1.8 quarry blast was recorded 9 km (6 mi) southwest of Jamestown, CA, at 10:35 am PDT on 18 August 2020 (17:35 UTC), less than 1 km deep.
USGS: 7km WNW of Chinese Camp, CA
53 km (33 mi) ENE of Modesto, CA · 134 km (83 mi) ENE of San Jose, CA
- When
- 10:35 am PDT on 18 August 2020 ()
- Where
- 9 km (6 mi) southwest of Jamestown, CA · earthquakes near Jamestown
- Magnitude
- M 1.8 (md)
- Depth
- -0.8 km below the surface
- Felt
- no reports yet
- Nearest
- Calaveras County, 33 km N
- Nearest mapped fault
- Foothills fault system, 3 km from its surface trace — near is not the same as on
- Status
- Reviewed by a seismologist
USGS · last changed by USGS · we first saw it 2277 days ago
Earthquake alerts for Jamestown, CA
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Alerts are on for .
Not a warning. An alert comes after USGS publishes a quake, usually minutes after the shaking. For early warning use ShakeAlert, through your phone's Wireless Emergency Alerts or the MyShake app.
This was a minor earthquake. Quakes this small are rarely felt and do not cause damage.
At this magnitude and depth, people at rest would likely notice it out to about 14 km (9 mi) from the epicentre. In Jamestown, 9 km away, the estimate is intensity II (weak). Estimated from magnitude, depth and distance with the intensity equation USGS Did You Feel It? uses; felt reports, where there are any, are the measurement.
Earthquakes near other towns within 30 km: Sonora, East Sonora, Copperopolis, Columbia, Angels Camp, Phoenix Lake.
USGS catalogues this as quarry blast, not an earthquake.
How big was it?
This earthquake released about 15 lb of TNT. Magnitude is logarithmic: each whole step up releases about 32 times more energy, so a magnitude 2.8 would have released about 32 times as much.
- Mineral, Virginia 2011 M 5.8 1,000,000× the energy of this one
- Magna, Utah 2020 M 5.7 710,000× the energy of this one
- Around the size people start to feel M 3.0 63× the energy of this one
- This earthquake M 1.8 about 15 lb of TNT
Energy from the Gutenberg–Richter relation (log10E = 1.5M + 4.8), rounded to two figures; bar length is magnitude, which is already a logarithm of energy. Magnitudes of past earthquakes from the USGS catalogue.
For this area
No earthquake of M4 or more has been recorded within 50 km since our catalogue begins in 2016.
Before 2016, the USGS record since 1900 lists no earthquake of M5 or more within 50 km.
Since 2016: the QuakeIndex catalogue (US, M1.5+), built from the USGS FDSN event service. Before 2016: USGS ComCat, M5+ from 1900. Distances are between epicentres. This is the record, not a forecast.
Where
Epicentre 37.8987, -120.4997. Map © OpenStreetMap contributors.
Nearby places
| Place | Distance | Direction from the epicentre | |
|---|---|---|---|
| Calaveras County, CA | 33 km (20 mi) | N | earthquakes near Calaveras County |
| Tuolumne County, CA | 49 km (30 mi) | ENE | earthquakes near Tuolumne County |
| Stanislaus County, CA | 58 km (36 mi) | SW | earthquakes near Stanislaus County |
| Amador County, CA | 62 km (39 mi) | NNW | earthquakes near Amador County |
| Mariposa County, CA | 63 km (39 mi) | SE | earthquakes near Mariposa County |
| San Joaquin County, CA | 68 km (42 mi) | W | earthquakes near San Joaquin County |
Places and coordinates from the US Census Bureau Gazetteer (2024). Distances are from the epicentre.
Aftershocks so far
5 earthquakes have been recorded within 50 km since this one.
- 1.6 1 km NW of Forest Meadows, California
- 2.2 9 km NW of Chinese Camp, CA
- 1.9 18km E of Groveland-Big Oak Flat, CA
- 2.3 6km S of Vallecito, CA
- 2.1 11km E of Groveland-Big Oak Flat, CA
Counted from the QuakeIndex database, which ingests the USGS feed every 30 seconds · as of . QuakeIndex does not forecast aftershocks. When USGS issues an operational aftershock forecast it appears on the USGS event page.
On USGS
- The official USGS event page — the source of record for every value above
- Did you feel it? Report it to USGS — reports go to USGS, not to us
- ShakeMap for this event, when USGS has produced one
QuakeIndex does not issue warnings. For earthquake early warning see ShakeAlert.