Earthquake · reviewed by a seismologist
M 1.8md
Earthquake near Pacifica, CA
No earthquake was likely felt in Pacifica in the 24 hours to 11:03 am PST (19:03 UTC). The last one was M 2.7, 2 km (1 mi) NE, at 5:17 pm PDT on 28 October 2026, estimated intensity III (weak) in town; 526 felt reports to USGS. Every earthquake near Pacifica
This page: a magnitude 1.8 earthquake was recorded 2 km (2 mi) northwest of Pacifica, CA, at 6:18 pm PDT on 23 August 2021 (01:18 UTC), 8.3 km deep. 2 people have reported feeling it to USGS.
USGS: 2km NW of Pacifica, CA
19 km (12 mi) SSW of San Francisco, CA · 9 km (6 mi) SSW of Daly City, CA
- When
- 6:18 pm PDT on 23 August 2021 ()
- Where
- 2 km (2 mi) northwest of Pacifica, CA · earthquakes near Pacifica
- Magnitude
- M 1.8 (md)
- Depth
- 8.3 km below the surface
- Felt
- 2 reports · strongest reported intensity II
- Nearest
- San Mateo County, 27 km SSE
- Nearest mapped fault
- San Andreas fault, under 1 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 1903 days ago
Earthquake alerts for Pacifica, 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 10 km (6 mi) from the epicentre. In Pacifica, 2 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.
Likely felt in: Pacifica 2 km, intensity II · San Bruno 9 km, intensity II · South San Francisco 9 km, intensity II · Daly City 10 km, intensity II. Estimated for each town centre; each link is that town's own record.
How big was it?
This earthquake released about 13 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 1,200,000× the energy of this one
- Magna, Utah 2020 M 5.7 840,000× the energy of this one
- Around the size people start to feel M 3.0 75× the energy of this one
- This earthquake M 1.8 about 13 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
The largest earthquake within 50 km since 2016 was M 4.4 on 2018-01-04 — about 8,800 times the energy of this one.
Before 2016, the USGS record lists 2 earthquakes of M5 or more within 50 km:
- 7.9 The 1906 San Francisco, California Earthquake · 14 km NNW of this epicentre
- 5.3 The 1957 San Francisco, California Earthquake · 5 km NNE of this epicentre
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 37.6282, -122.5080. Map © OpenStreetMap contributors.
Nearby places
| Place | Distance | Direction from the epicentre | |
|---|---|---|---|
| San Mateo County, CA | 27 km (17 mi) | SSE | earthquakes near San Mateo County |
| San Francisco County, CA | 47 km (29 mi) | WNW | earthquakes near San Francisco County |
| Marin County, CA | 52 km (32 mi) | NNW | earthquakes near Marin County |
| Alameda County, CA | 52 km (33 mi) | E | earthquakes near Alameda County |
| Contra Costa County, CA | 59 km (36 mi) | ENE | earthquakes near Contra Costa County |
| Santa Cruz County, CA | 82 km (51 mi) | SSE | earthquakes near Santa Cruz County |
Places and coordinates from the US Census Bureau Gazetteer (2024). Distances are from the epicentre.
Aftershocks so far
33 earthquakes have been recorded within 50 km since this one.
- 2.3 1km W of Kensington, CA
- 2.6 1km W of Kensington, CA
- 1.6 6km N of San Leandro, CA
- 1.6 1km SSE of San Ramon, CA
- 1.5 2km SW of San Francisco Zoo, CA
- 1.6 4km ENE of Burlingame, CA
- 1.6 1km SW of Alamo, CA
- 2.0 4km ENE of El Sobrante, CA
- 2.8 4km ENE of El Sobrante, CA
- 2.1 4km ENE of El Sobrante, CA
- 1.9 1km S of San Ramon, CA
- 1.6 4km SSW of San Francisco Zoo, CA
- 2.1 4km WSW of Alamo, CA
- 2.1 6km SSW of Moraga, CA
- 1.9 5km SW of Pacheco, 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.