Earthquake · reviewed by a seismologist
M 1.6md
Earthquake near Pacifica, CA
USGS: 2 km NE of Pacifica, California
17 km (11 mi) SSW of San Francisco, CA · 8 km (5 mi) WSW of South San Francisco, CA
- When
- 7:50 pm PST on 21 December 2016 ()
- Where
- 2 km (2 mi) NE of Pacifica, CA · earthquakes near Pacifica
- Magnitude
- M 1.6 (md)
- Depth
- 6.9 km below the surface
- Felt
- no reports yet
- Nearest
- San Mateo County, 25 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 3521 days ago
A magnitude 1.6 earthquake was recorded 2 km (2 mi) NE of Pacifica, CA, at 7:50 pm PST on 21 December 2016 (03:50 UTC). This was a minor earthquake. Quakes this small are rarely felt and do not cause damage.
Earthquakes near other towns within 30 km: San Bruno, Colma, South San Francisco, Broadmoor, Millbrae, Brisbane.
How big was it?
This earthquake released about 6.4 lb of TNT. Magnitude is logarithmic: each whole step up releases about 32 times more energy, so a magnitude 2.5 would have released about 32 times as much.
- Mineral, Virginia 2011 M 5.8 2,400,000× the energy of this one
- Magna, Utah 2020 M 5.7 1,700,000× the energy of this one
- Around the size people start to feel M 3.0 150× the energy of this one
- This earthquake M 1.6 about 6.4 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 lists 2 earthquakes of M5 or more within 50 km:
- 7.9 The 1906 San Francisco, California Earthquake · 16 km NNW of this epicentre
- 5.3 The 1957 San Francisco, California Earthquake · 5 km NNW 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 37.6265, -122.4635. Map © OpenStreetMap contributors.
Nearby places
| Place | Distance | Direction from the epicentre | |
|---|---|---|---|
| San Mateo County, CA | 25 km (15 mi) | SSE | earthquakes near San Mateo County |
| Alameda County, CA | 49 km (30 mi) | E | earthquakes near Alameda County |
| San Francisco County, CA | 51 km (32 mi) | WNW | earthquakes near San Francisco County |
| Marin County, CA | 53 km (33 mi) | NNW | earthquakes near Marin County |
| Contra Costa County, CA | 56 km (35 mi) | NE | earthquakes near Contra Costa County |
| Santa Cruz County, CA | 79 km (49 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
47 earthquakes have been recorded within 50 km since this one.
- 1.5 Northern California
- 1.7 1 km ENE of Berkeley, California
- 2.3 2 km N of Union City, California
- 1.7 3 km S of Loyola, California
- 1.6 4 km W of Pleasant Hill, California
- 1.6 7 km SSE of Pescadero, California
- 2.5 7 km S of Pescadero, California
- 1.6 Northern California
- 1.5 5 km ESE of Fremont, California
- 1.6 6 km SW of Loyola, California
- 1.5 3 km S of Loyola, California
- 1.9 1 km NNE of Pacifica, California
- 1.7 4 km SW of Broadmoor, California
- 1.6 4 km SW of Broadmoor, California
- 1.8 4 km SW of Broadmoor, California
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.