QuakeIndex

Earthquake · reviewed by a seismologist

M 2.8md

Earthquake near Los Altos Hills, CA

No earthquake was likely felt in Los Altos Hills in the 24 hours to 6:57 pm PST (02:57 UTC). The last one was M 2.0, 10 km (6 mi) SE, at 9:23 am PST on 10 November 2026, estimated intensity II (weak) in town; 4 felt reports to USGS. Every earthquake near Los Altos Hills

This page: a magnitude 2.8 earthquake was recorded 3 km (2 mi) south of Los Altos Hills, CA, at 8:26 pm PST on 29 December 2020 (04:26 UTC), 6.5 km deep. 403 people have reported feeling it to USGS.

USGS: 3km S of Los Altos Hills, CA

30 km (18 mi) WNW of San Jose, CA · in Palo Alto, CA

8:26 pm PST, Dec 29, 2020 · · 6.5 km deep · released about 480 lb of TNT

Every earthquake near Los Altos Hills Felt it? Tell USGS Check my area
10 km30 km60 km120 km N San Mateo County 21 kmAlameda County 38 kmSanta Cruz County 40 kmSanta Clara County 43 kmContra Costa County 65 kmSan Francisco County 89 kmMarin County 94 kmSan Joaquin County 100 kmSolano County 103 km
Distance rings around the epicentre, with the nearest towns at their true direction and later quakes as coloured dots. Not a shaking map — see the USGS ShakeMap for that.
When
8:26 pm PST on 29 December 2020 ()
Where
3 km (2 mi) south of Los Altos Hills, CA · earthquakes near Los Altos Hills
Magnitude
M 2.8 (md)
Depth
6.5 km below the surface
Felt
403 reports · strongest reported intensity III
Nearest
San Mateo County, 21 km WNW
Nearest mapped fault
Monte Vista-Shannon fault, 2 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 1479 days ago

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 26 km (16 mi) from the epicentre. In Los Altos Hills, 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: Los Altos 4 km, intensity III · Mountain View 6 km, intensity III · Sunnyvale 9 km, intensity III · Palo Alto 10 km, intensity III · Cupertino 10 km, intensity III · Menlo Park 12 km, intensity III · East Palo Alto 13 km, intensity III · Saratoga 15 km, intensity II. Estimated for each town centre; each link is that town's own record.

How big was it?

This earthquake released about 480 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 32,000× the energy of this one
  2. Magna, Utah 2020 M 5.7 22,000× the energy of this one
  3. Around the size people start to feel M 3.0 2× the energy of this one
  4. This earthquake M 2.8 about 480 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 86 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 · 42 km SSE of this epicentre
  2. 6.2 Near San Jose, California · 31 km E of this epicentre
  3. 6.2 The 1984 Morgan Hill, California Earthquake · 41 km E of this epicentre
  4. 6.1 Near San Jose, California · 35 km ESE of this epicentre
  5. 5.8 7 km NNW of Boulder Creek, California · 18 km S 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 37.3543, -122.1412. Map © OpenStreetMap contributors.

Nearby places

PlaceDistanceDirection from the epicentre
San Mateo County, CA 21 km (13 mi) WNW earthquakes near San Mateo County
Alameda County, CA 38 km (24 mi) NNE earthquakes near Alameda County
Santa Cruz County, CA 40 km (25 mi) SSE earthquakes near Santa Cruz County
Santa Clara County, CA 43 km (26 mi) ESE earthquakes near Santa Clara County
Contra Costa County, CA 65 km (40 mi) NNE earthquakes near Contra Costa County
San Francisco County, CA 89 km (55 mi) WNW earthquakes near San Francisco County

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

Aftershocks so far

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

  1. 2.1 4km WSW of Pleasanton, CA
  2. 1.9 9km NNE of Alum Rock, CA
  3. 2.6 7km E of Alum Rock, CA
  4. 2.5 15km ENE of Alum Rock, CA
  5. 1.7 10km SE of Sunol, CA
  6. 2.5 15km N of Morgan Hill, CA
  7. 1.6 16km N of Morgan Hill, CA
  8. 2.1 10km SE of Sunol, CA
  9. 2.0 15km E of Seven Trees, CA
  10. 1.6 6km ESE of Fairview, CA
  11. 1.9 6km E of Milpitas, CA
  12. 1.6 5km E of Alum Rock, CA
  13. 2.1 11km NE of Milpitas, CA
  14. 2.6 1km ENE of Union City, CA
  15. 1.9 16km E of Seven Trees, 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

QuakeIndex does not issue warnings. For earthquake early warning see ShakeAlert.