Earthquake · reviewed by a seismologist
M 3.4ml
Earthquake near Alpine, CA
No earthquake was likely felt in Alpine in the 24 hours to 12:51 pm PST (20:51 UTC). The last one was M 4.9, 155 km (96 mi) ESE, at 10:27 am PST on 3 November 2026, estimated intensity II (weak) in town; 321 felt reports to USGS. Every earthquake near Alpine
This page: a magnitude 3.4 earthquake was recorded 48 km (30 mi) east-northeast of Alpine, CA, at 3:30 am PDT on 20 October 2020 (10:30 UTC), 7.1 km deep. 17 people have reported feeling it to USGS.
USGS: 21km SW of Ocotillo Wells, CA
82 km (51 mi) ENE of San Diego, CA
- When
- 3:30 am PDT on 20 October 2020 ()
- Where
- 48 km (30 mi) east-northeast of Alpine, CA · earthquakes near Alpine
- Magnitude
- M 3.4 (ml)
- Depth
- 7.1 km below the surface
- Felt
- 17 reports · strongest reported intensity IV
- Measured shaking
- intensity III (ShakeMap)
- Nearest
- San Diego County, 45 km W
- Nearest mapped fault
- Elsinore fault, 8 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 2144 days ago
Earthquake alerts for Alpine, CA
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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 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 60 km (37 mi) from the epicentre. In Alpine, 48 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: Borrego Springs 29 km, intensity II · Julian 30 km, intensity II · Pine Valley 30 km, intensity II · Salton City 45 km, intensity II · San Diego Country Estates 46 km, intensity II · Campo 47 km, intensity II · Alpine 48 km, intensity II. Estimated for each town centre; each link is that town's own record.
How big was it?
This earthquake released about 2.2 tons of TNT. Magnitude is logarithmic: each whole step up releases about 32 times more energy, so a magnitude 4.4 would have released about 32 times as much.
- Northridge, California 1994 M 6.7 78,000× the energy of this one
- Mineral, Virginia 2011 M 5.8 3,500× the energy of this one
- Magna, Utah 2020 M 5.7 2,500× the energy of this one
- This earthquake M 3.4 about 2.2 tons of TNT
- Around the size people start to feel M 3.0 this one released 4.6× more
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 5.2 on 2016-06-10 — about 420 times the energy of this one.
Before 2016, the USGS record lists 17 earthquakes of M5 or more within 50 km; the five largest:
- 6.6 The 1942 Fish Creek Mountains, California Earthquake · 47 km E of this epicentre
- 6.6 The 1968 Borrego Mountain, California Earthquake · 26 km NE of this epicentre
- 6.6 The 1987 Superstition Hills, California Earthquake · 41 km E of this epicentre
- 6.4 The 1954 San Jacinto Fault, California Earthquake · 38 km NNE of this epicentre
- 6.2 The 1987 Elmore Ranch, California Earthquake · 47 km ENE 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 33.0053, -116.2895. Map © OpenStreetMap contributors.
Nearby places
| Place | Distance | Direction from the epicentre | |
|---|---|---|---|
| San Diego County, CA | 45 km (28 mi) | W | earthquakes near San Diego County |
| Riverside County, CA | 85 km (53 mi) | NNE | earthquakes near Riverside County |
| Imperial County, CA | 87 km (54 mi) | E | earthquakes near Imperial 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.
- 1.6 27km SSW of Ocotillo Wells, CA
- 1.8 20km E of Julian, CA
- 1.5 20km WNW of Imperial, CA
- 1.9 14km ENE of Borrego Springs, CA
- 1.7 24km ESE of Julian, CA
- 2.5 5km SW of Salton City, CA
- 1.5 13km E of Ocotillo Wells, CA
- 1.6 12km E of Ocotillo Wells, CA
- 1.6 16km N of Borrego Springs, CA
- 3.6 6km SSW of Warner Springs, CA
- 1.5 18km NNE of Ocotillo, CA
- 1.5 18km NNE of Ocotillo, CA
- 1.7 12km NE of Julian, CA
- 1.7 10km NNE of Ocotillo Wells, CA
- 2.4 10km NNE of Ocotillo Wells, 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.