Earthquake near Half Moon Bay, CA

This was a small earthquake. Shaking like this is often felt indoors nearby and very rarely causes damage.

At this magnitude and depth, people at rest would likely notice it out to about 27 km (17 mi) from the epicentre. In Half Moon Bay, 3 km away, the estimate is intensity III (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: Half Moon Bay 3 km, intensity III · Belmont 16 km, intensity II · San Mateo 16 km, intensity II · San Carlos 16 km, intensity II · Burlingame 17 km, intensity II · Redwood City 17 km, intensity II · Millbrae 18 km, intensity II · Foster City 19 km, intensity II. Estimated for each town centre; each link is that town's own record.

How big was it?

This earthquake released about 530 lb of TNT. Magnitude is logarithmic: each whole step up releases about 32 times more energy, so a magnitude 3.8 would have released about 32 times as much.

1. Mineral, Virginia 2011 M 5.8 29,000× the energy of this one
2. Magna, Utah 2020 M 5.7 20,000× the energy of this one
3. Around the size people start to feel M 3.0 1.8× the energy of this one
4. This earthquake M 2.8 about 530 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 210 times the energy of this one.

Before 2016, the USGS record lists 6 earthquakes of M5 or more within 50 km; the five largest:

1. 7.9 The 1906 San Francisco, California Earthquake · 36 km NNW of this epicentre Apr 18, 1906
2. 5.8 7 km NNW of Boulder Creek, California · 37 km SE of this epicentre Sep 5, 1955
3. 5.5 Santa Cruz Mountains, California · 48 km SE of this epicentre Nov 9, 1914
4. 5.3 The 1957 San Francisco, California Earthquake · 26 km NNW of this epicentre Mar 22, 1957
5. 5.1 7 km SW of Monte Sereno, California · 43 km SE of this epicentre Oct 18, 1989

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 37.4402, -122.4242. Map © OpenStreetMap contributors.

Nearby places

Places and coordinates from the US Census Bureau Gazetteer (2024). Distances are from the epicentre.

Aftershocks so far

50 earthquakes have been recorded within 50 km since this one.

1. 1.6 4km SW of San Bruno, CA 22:36 UTC
2. 2.2 4km SW of San Bruno, CA 20:56 UTC
3. 2.3 1km ENE of Pacifica, CA 03:16 UTC
4. 2.0 1km ENE of Pacifica, CA 16:25 UTC
5. 2.6 1km ENE of Pacifica, CA 13:04 UTC
6. 2.6 1km ENE of Pacifica, CA 13:03 UTC
7. 3.4 1km ENE of Pacifica, CA 13:01 UTC
8. 1.7 10km WNW of San Francisco Zoo, CA 05:13 UTC
9. 1.6 1km SSE of Portola Valley, CA 20:39 UTC
10. 1.8 3km NNW of Emeryville, CA 23:18 UTC
11. 1.6 2km S of Oakland, CA 23:05 UTC
12. 1.9 3km E of Hayward, CA 18:41 UTC
13. 2.0 2km ESE of Berkeley, CA 21:52 UTC
14. 1.5 6km WNW of Sunol, CA 12:34 UTC
15. 2.2 4km WSW of Colma, CA 23:23 UTC

Counted from the QuakeIndex database, which ingests the USGS feed every 30 seconds · as of 07:33 UTC. 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.