Earthquake · reviewed by a seismologist
M 4.0mw
Earthquake near Redway, CA
No earthquake was likely felt in Redway in the 24 hours to 11:37 pm PST (07:37 UTC). The last one was M 5.0, 153 km (95 mi) WNW, at 8:56 pm PST on 4 November 2026, estimated intensity II (weak) in town; 145 felt reports to USGS. Every earthquake near Redway
This page: a magnitude 4.0 earthquake was recorded 21 km (13 mi) east-northeast of Redway, CA, at 2:48 am PDT on 20 April 2021 (09:48 UTC), 34 km deep. 26 people have reported feeling it to USGS.
USGS: 20km ENE of Redway, CA
- When
- 2:48 am PDT on 20 April 2021 ()
- Where
- 21 km (13 mi) east-northeast of Redway, CA · earthquakes near Redway
- Magnitude
- M 4.0 (mw)
- Depth
- 34 km below the surface
- Felt
- 26 reports · strongest reported intensity IV
- Measured shaking
- intensity III (ShakeMap)
- USGS impact alert
- green
- Nearest
- Humboldt County, 64 km NNW
- Nearest mapped fault
- Bartlett Springs fault system, 9 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 1958 days ago
Earthquake alerts for Redway, CA
Get a notification in this browser when USGS records an earthquake near Redway, 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 light earthquake. It is usually felt clearly nearby and can rattle windows and dishes, but damage is uncommon.
At this magnitude and depth, people at rest would likely notice it out to about 93 km (58 mi) from the epicentre. In Redway, 21 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: Redway 21 km, intensity III. Estimated for each town centre; each link is that town's own record.
How big was it?
This earthquake released about 17 tons of TNT. Magnitude is logarithmic: each whole step up releases about 32 times more energy, so a magnitude 5.0 would have released about 32 times as much.
- Northridge, California 1994 M 6.7 10,000× the energy of this one
- Mineral, Virginia 2011 M 5.8 450× the energy of this one
- Magna, Utah 2020 M 5.7 320× the energy of this one
- This earthquake M 4.0 about 17 tons of TNT
- Around the size people start to feel M 3.0 this one released 35× 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 4.5 on 2016-08-28 — about 4.9 times the energy of this one.
Before 2016, the USGS record lists 2 earthquakes of M5 or more within 50 km:
- 5.9 9 km S of Leggett, California · 47 km SSW of this epicentre
- 5.5 7 km ESE of Shelter Cove, California · 40 km WSW 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 40.1880, -123.5988. Map © OpenStreetMap contributors.
Nearby places
| Place | Distance | Direction from the epicentre | |
|---|---|---|---|
| Humboldt County, CA | 64 km (40 mi) | NNW | earthquakes near Humboldt County |
| Trinity County, CA | 66 km (41 mi) | NE | earthquakes near Trinity County |
| Mendocino County, CA | 85 km (53 mi) | S | earthquakes near Mendocino County |
| Tehama County, CA | 116 km (72 mi) | E | earthquakes near Tehama County |
| Glenn County, CA | 121 km (75 mi) | ESE | earthquakes near Glenn County |
| Colusa County, CA | 162 km (101 mi) | SE | earthquakes near Colusa County |
Places and coordinates from the US Census Bureau Gazetteer (2024). Distances are from the epicentre.
Aftershocks so far
49 earthquakes have been recorded within 50 km since this one.
- 2.0 16km NNE of Redway, CA
- 1.7 15km ESE of Hydesville, CA
- 1.9 14km NNE of Laytonville, CA
- 1.8 20km SSE of Rio Dell, CA
- 1.9 20km SSE of Rio Dell, CA
- 2.3 20km NNE of Redway, CA
- 2.6 15km SE of Petrolia, CA
- 1.7 2km N of Redway, CA
- 4.1 19km NW of Covelo, CA
- 2.0 28km NE of Redway, CA
- 1.6 5km NW of Redway, CA
- 1.9 8km SSE of Redway, CA
- 2.0 8km SSE of Redway, CA
- 1.8 18km E of Rio Dell, CA
- 2.0 18km E of Rio Dell, 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.