Earthquake near Portola Valley, 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 30 km (19 mi) from the epicentre. In Portola Valley, 4 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: Portola Valley 4 km, intensity III · Stanford 9 km, intensity III · Los Altos 9 km, intensity III · Loyola 10 km, intensity III · Menlo Park 11 km, intensity III · Palo Alto 12 km, intensity III · Mountain View 12 km, intensity III · East Palo Alto 14 km, intensity II. Estimated for each town centre; each link is that town's own record.

How big was it?

This earthquake released about 680 lb of TNT. Magnitude is logarithmic: each whole step up releases about 32 times more energy, so a magnitude 3.9 would have released about 32 times as much.

1. Mineral, Virginia 2011 M 5.8 22,000× the energy of this one
2. Magna, Utah 2020 M 5.7 16,000× the energy of this one
3. Around the size people start to feel M 3.0 1.4× the energy of this one
4. This earthquake M 2.9 about 680 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 17 earthquakes of M5 or more within 50 km; the five largest:

1. 6.9 The 1989 Loma Prieta, California Earthquake · 46 km SE of this epicentre Oct 18, 1989
2. 6.3 16 km SW of Davenport, California · 49 km SSW of this epicentre Oct 22, 1926
3. 6.2 Near San Jose, California · 37 km E of this epicentre Aug 3, 1903
4. 6.2 The 1984 Morgan Hill, California Earthquake · 47 km E of this epicentre Apr 24, 1984
5. 6.1 Near San Jose, California · 40 km ESE of this epicentre Jun 11, 1903

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 37.3528, -122.2100. Map © OpenStreetMap contributors.

Nearby places

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

Aftershocks so far

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

1. 2.6 4 km ESE of Union City, California 17:29 UTC
2. 1.7 11 km SE of Sunol, California 11:36 UTC
3. 2.8 8 km NNE of East Foothills, California 00:27 UTC
4. 1.5 3 km S of Loyola, California 21:23 UTC
5. 1.7 3 km NE of Sunol, California 06:55 UTC
6. 2.4 8 km N of East Foothills, California 17:06 UTC
7. 1.8 7 km NE of Day Valley, California 07:06 UTC
8. 1.6 2 km E of Union City, California 00:21 UTC
9. 2.0 4 km NNW of Union City, California 17:48 UTC
10. 2.2 9 km SSE of Sunol, California 19:28 UTC
11. 2.5 2 km N of San Leandro, California 14:37 UTC
12. 2.2 6 km NE of East Foothills, California 14:27 UTC
13. 2.9 2 km E of San Leandro, California 21:19 UTC
14. 1.8 3 km S of Loyola, California 21:15 UTC
15. 2.1 6 km ESE of East Foothills, California 06:22 UTC

Counted from the QuakeIndex database, which ingests the USGS feed every 30 seconds · as of 08:42 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.