Earthquake · reviewed by a seismologist
M 3.1ml
Earthquake near Ridgemark, CA
No earthquake was likely felt in Ridgemark in the 24 hours to 9:48 pm PST (05:48 UTC). The last one was M 2.4, 8 km (5 mi) S, at 8:53 pm PST on 5 November 2026, estimated intensity II (weak) in town; 1 felt report to USGS. Every earthquake near Ridgemark
This page: a magnitude 3.1 earthquake was recorded 5 km (3 mi) south of Ridgemark, CA, at 12:54 pm PDT on 21 August 2021 (19:54 UTC), 9.3 km deep. 17 people have reported feeling it to USGS.
USGS: 5km S of Ridgemark, CA
70 km (44 mi) SE of San Jose, CA · 25 km (15 mi) ENE of Salinas, CA
- When
- 12:54 pm PDT on 21 August 2021 ()
- Where
- 5 km (3 mi) south of Ridgemark, CA · earthquakes near Ridgemark
- Magnitude
- M 3.1 (ml)
- Depth
- 9.3 km below the surface
- Felt
- 17 reports · strongest reported intensity III
- Nearest
- San Benito County, 31 km SE
- Nearest mapped fault
- San Andreas fault, 3 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 1836 days ago
Earthquake alerts for Ridgemark, CA
Get a notification in this browser when USGS records an earthquake near Ridgemark, 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 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 41 km (25 mi) from the epicentre. In Ridgemark, 5 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: Hollister 9 km, intensity III · Prunedale 26 km, intensity II · Salinas 27 km, intensity II · Gilroy 31 km, intensity II · Watsonville 37 km, intensity II · Soledad 39 km, intensity II. Estimated for each town centre; each link is that town's own record.
How big was it?
This earthquake released about 1,300 lb of TNT. Magnitude is logarithmic: each whole step up releases about 32 times more energy, so a magnitude 4.1 would have released about 32 times as much.
- Northridge, California 1994 M 6.7 250,000× the energy of this one
- Mineral, Virginia 2011 M 5.8 11,000× the energy of this one
- Magna, Utah 2020 M 5.7 7,900× the energy of this one
- This earthquake M 3.1 about 1,300 lb of TNT
- Around the size people start to feel M 3.0 this one released 1.4× 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 4.7 on 2019-10-15 — about 260 times the energy of this one.
Before 2016, the USGS record lists 24 earthquakes of M5 or more within 50 km; the five largest:
- 6.5 Near Morgan Hill, California · 44 km NNW of this epicentre
- 5.9 10 km SE of Tres Pinos, California · 14 km ESE of this epicentre
- 5.8 Near Watsonville, California · 35 km NW of this epicentre
- 5.8 Near Paicines, California · 16 km SE of this epicentre
- 5.8 The 1979 Coyote Lake, California Earthquake · 39 km NNW 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 36.7720, -121.3740. Map © OpenStreetMap contributors.
Nearby places
| Place | Distance | Direction from the epicentre | |
|---|---|---|---|
| San Benito County, CA | 31 km (19 mi) | SE | earthquakes near San Benito County |
| Santa Clara County, CA | 57 km (36 mi) | NNW | earthquakes near Santa Clara County |
| Monterey County, CA | 59 km (37 mi) | S | earthquakes near Monterey County |
| Santa Cruz County, CA | 62 km (39 mi) | WNW | earthquakes near Santa Cruz County |
| Merced County, CA | 75 km (46 mi) | NE | earthquakes near Merced County |
| Stanislaus County, CA | 94 km (58 mi) | NNE | earthquakes near Stanislaus County |
Places and coordinates from the US Census Bureau Gazetteer (2024). Distances are from the epicentre.
Aftershocks so far
59 earthquakes have been recorded within 50 km since this one.
- 1.8 14km WNW of Pinnacles, CA
- 2.4 6km SE of Pinnacles, CA
- 2.0 7km ESE of Pinnacles, CA
- 1.5 17km SSE of Tres Pinos, CA
- 3.7 14km WNW of Pinnacles, CA
- 2.2 7km SE of Pinnacles, CA
- 1.5 16km SSE of Tres Pinos, CA
- 2.0 14km SSE of Tres Pinos, CA
- 1.8 14km SSE of Tres Pinos, CA
- 1.5 4km NNW of Pinnacles, CA
- 2.0 7km NNW of Pinnacles, CA
- 2.8 6km NW of Pinnacles, CA
- 2.0 14km SSE of Tres Pinos, CA
- 1.7 5km S of San Juan Bautista, CA
- 2.8 12km W of Moss Landing, 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.