Earthquake near Portola Valley, CA

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 20 km (12 mi) from the epicentre. In Portola Valley, 6 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: Los Altos 10 km, intensity II · Mountain View 12 km, intensity II · Palo Alto 13 km, intensity II · Menlo Park 13 km, intensity II · Cupertino 15 km, intensity II · Sunnyvale 15 km, intensity II · East Palo Alto 16 km, intensity II · Redwood City 17 km, intensity II. Estimated for each town centre; each link is that town's own record.

How big was it?

This earthquake released about 160 lb of TNT. Magnitude is logarithmic: each whole step up releases about 32 times more energy, so a magnitude 3.5 would have released about 32 times as much.

1. Mineral, Virginia 2011 M 5.8 95,000× the energy of this one
2. Magna, Utah 2020 M 5.7 68,000× the energy of this one
3. Around the size people start to feel M 3.0 6× the energy of this one
4. This earthquake M 2.5 about 160 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 4.1 on 2017-10-10 — about 260 times the energy of this one.

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 · 44 km SE of this epicentre Oct 18, 1989
2. 6.3 16 km SW of Davenport, California · 47 km SSW of this epicentre Oct 22, 1926
3. 6.2 Near San Jose, California · 36 km E of this epicentre Aug 3, 1903
4. 6.2 The 1984 Morgan Hill, California Earthquake · 46 km E of this epicentre Apr 24, 1984
5. 6.1 Near San Jose, California · 39 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 37.3357, -122.2023. Map © OpenStreetMap contributors.

Nearby places

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

Aftershocks so far

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

1. 1.5 2km S of Dublin, CA 06:41 UTC
2. 1.8 9km NNE of Alum Rock, CA 01:05 UTC
3. 2.1 15km ENE of Seven Trees, CA 02:09 UTC
4. 1.8 6km SSE of Portola Valley, CA 14:40 UTC
5. 1.9 6km SSE of Portola Valley, CA 14:18 UTC
6. 2.1 2km NNE of San Leandro, CA 14:10 UTC
7. 1.7 4km WNW of Dublin, CA 08:57 UTC
8. 2.6 4km WSW of Colma, CA 23:27 UTC
9. 1.6 11km NE of Milpitas, CA 02:44 UTC
10. 2.2 10km SE of Sunol, CA 20:03 UTC
11. 2.1 10km ESE of Fremont, CA 18:40 UTC
12. 1.8 2km WNW of Los Altos Hills, CA 18:44 UTC
13. 1.9 6km SSE of Portola Valley, CA 02:41 UTC
14. 1.7 7km SSE of Portola Valley, CA 16:48 UTC
15. 1.8 6km SSE of Portola Valley, CA 16:17 UTC

Counted from the QuakeIndex database, which ingests the USGS feed every 30 seconds · as of 11:33 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.