Earthquake · reviewed by a seismologist
M 1.8md
Earthquake near Los Altos Hills, CA
No earthquake was likely felt in Los Altos Hills in the 24 hours to 3:04 am PST (11:04 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 1.8 earthquake was recorded 2 km (1 mi) south of Los Altos Hills, CA, at 11:21 am PST on 27 December 2020 (19:21 UTC), 5.0 km deep. 5 people have reported feeling it to USGS.
USGS: 2km S of Los Altos Hills, CA
30 km (19 mi) WNW of San Jose, CA · in Palo Alto, CA
- When
- 11:21 am PST on 27 December 2020 ()
- Where
- 2 km (1 mi) south of Los Altos Hills, CA · earthquakes near Los Altos Hills
- Magnitude
- M 1.8 (md)
- Depth
- 5.0 km below the surface
- Felt
- 5 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 2137 days ago
Earthquake alerts for Los Altos Hills, CA
Get a notification in this browser when USGS records an earthquake near Los Altos Hills, CA. No account or email needed.
Alerts are on for .
Not a warning. An alert comes after USGS publishes a quake, usually minutes after the shaking. For early warning use ShakeAlert, through your phone's Wireless Emergency Alerts or the MyShake app.
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 12 km (7 mi) from the epicentre. In Los Altos Hills, 2 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 4 km, intensity II · Mountain View 6 km, intensity II · Palo Alto 9 km, intensity II · Sunnyvale 9 km, intensity II · Cupertino 10 km, intensity II · Menlo Park 11 km, intensity II · East Palo Alto 12 km, intensity II. Estimated for each town centre; each link is that town's own record.
How big was it?
This earthquake released about 13 lb of TNT. Magnitude is logarithmic: each whole step up releases about 32 times more energy, so a magnitude 2.8 would have released about 32 times as much.
- Mineral, Virginia 2011 M 5.8 1,100,000× the energy of this one
- Magna, Utah 2020 M 5.7 810,000× the energy of this one
- Around the size people start to feel M 3.0 72× the energy of this one
- This earthquake M 1.8 about 13 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 3,100 times the energy of this one.
Before 2016, the USGS record lists 17 earthquakes of M5 or more within 50 km; the five largest:
- 6.9 The 1989 Loma Prieta, California Earthquake · 43 km SSE of this epicentre
- 6.2 Near San Jose, California · 31 km ESE of this epicentre
- 6.2 The 1984 Morgan Hill, California Earthquake · 41 km E of this epicentre
- 6.1 Near San Jose, California · 35 km ESE of this epicentre
- 5.8 7 km NNW of Boulder Creek, California · 19 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 37.3583, -122.1423. Map © OpenStreetMap contributors.
Nearby places
| Place | Distance | Direction 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 (27 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
43 earthquakes have been recorded within 50 km since this one.
- 2.5 15km ENE of Alum Rock, CA
- 1.7 10km SE of Sunol, CA
- 2.5 15km N of Morgan Hill, CA
- 1.6 16km N of Morgan Hill, CA
- 2.1 10km SE of Sunol, CA
- 2.0 15km E of Seven Trees, CA
- 1.6 6km ESE of Fairview, CA
- 1.9 6km E of Milpitas, CA
- 1.6 5km E of Alum Rock, CA
- 2.1 11km NE of Milpitas, CA
- 2.6 1km ENE of Union City, CA
- 1.9 16km E of Seven Trees, CA
- 1.6 8km ESE of Fremont, CA
- 1.8 4km NE of Pleasanton, CA
- 2.7 8km ESE of Fremont, 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
- 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.