Earthquake · reviewed by a seismologist
M 2.8md
Earthquake near Cobb, CA
Yes: an earthquake was likely felt in Cobb in the last 24 hours. M 1.6, 4 km (2 mi) W of Cobb, at 6:16 am PST on 12 November 2026 (14:16 UTC); the estimated shaking in Cobb was intensity II (weak). Every earthquake near Cobb
This page: a magnitude 2.8 earthquake was recorded 8 km (5 mi) south of Cobb, CA, at 4:22 am PDT on 31 July 2017 (11:22 UTC), 1.8 km deep. 4 people have reported feeling it to USGS.
USGS: 8 km S of Cobb, California
34 km (21 mi) N of Santa Rosa, CA · 111 km (69 mi) NNW of San Francisco, CA
- When
- 4:22 am PDT on 31 July 2017 ()
- Where
- 8 km (5 mi) south of Cobb, CA · earthquakes near Cobb
- Magnitude
- M 2.8 (md)
- Depth
- 1.8 km below the surface
- Felt
- 4 reports · strongest reported intensity IV
- Nearest
- Sonoma County, 30 km SW
- Nearest mapped fault
- Maacama fault, 10 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 3381 days ago
Earthquake alerts for Cobb, CA
Get a notification in this browser when USGS records an earthquake near Cobb, 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 26 km (16 mi) from the epicentre. In Cobb, 8 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: Cobb 8 km, intensity III · Healdsburg 20 km, intensity II · Calistoga 22 km, intensity II · Windsor 24 km, intensity II · Clearlake 25 km, intensity II. Estimated for each town centre; each link is that town's own record.
How big was it?
This earthquake released about 430 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.
- Mineral, Virginia 2011 M 5.8 35,000× the energy of this one
- Magna, Utah 2020 M 5.7 25,000× the energy of this one
- Around the size people start to feel M 3.0 2.2× the energy of this one
- This earthquake M 2.8 about 430 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 5.0 on 2016-12-14 — about 2,300 times the energy of this one.
Before 2016, the USGS record lists 2 earthquakes of M5 or more within 50 km:
- 5.3 3 km E of Bloomfield, California · 49 km S of this epicentre
- 5.3 Northern California · 48 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 38.7478, -122.7218. Map © OpenStreetMap contributors.
Nearby places
| Place | Distance | Direction from the epicentre | |
|---|---|---|---|
| Sonoma County, CA | 30 km (19 mi) | SW | earthquakes near Sonoma County |
| Lake County, CA | 40 km (25 mi) | N | earthquakes near Lake County |
| Napa County, CA | 44 km (27 mi) | SE | earthquakes near Napa County |
| Colusa County, CA | 64 km (39 mi) | NE | earthquakes near Colusa County |
| Yolo County, CA | 71 km (44 mi) | E | earthquakes near Yolo County |
| Marin County, CA | 77 km (48 mi) | S | earthquakes near Marin County |
Places and coordinates from the US Census Bureau Gazetteer (2024). Distances are from the epicentre.
Aftershocks so far
58 earthquakes have been recorded within 50 km since this one.
- 1.7 5 km S of Cobb, California
- 1.6 5 km WNW of Cobb, California
- 1.6 5 km SSW of Cobb, California
- 1.9 4 km SSW of Cobb, California
- 1.6 5 km SSW of Cobb, California
- 1.9 8 km W of Cobb, California
- 1.8 5km NW of The Geysers, CA
- 2.1 6 km WSW of Cobb, California
- 1.6 7km NW of The Geysers, CA
- 1.6 1km NNW of The Geysers, CA
- 3.5 5 km WSW of Cobb, California
- 2.5 12 km ENE of Cloverdale, California
- 1.6 2km NW of The Geysers, CA
- 1.8 1km SSW of Anderson Springs, CA
- 1.9 3 km W of Cobb, California
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.