Earthquake · reviewed by a seismologist
M 1.8md
Earthquake near Rancho Tehama Reserve, CA
No earthquake was likely felt in Rancho Tehama Reserve in the 24 hours to 9:18 pm PST (05:18 UTC). The last one was M 4.0, 74 km (46 mi) SW, at 5:01 am PDT on 28 October 2026, estimated intensity II (weak) in town; 14 felt reports to USGS. Every earthquake near Rancho Tehama Reserve
This page: a magnitude 1.8 earthquake was recorded 37 km (23 mi) west of Rancho Tehama Reserve, CA, at 1:37 pm PDT on 27 September 2018 (20:37 UTC), 10 km deep.
USGS: 37km NNW of Alder Springs, CA
90 km (56 mi) WNW of Chico, CA
- When
- 1:37 pm PDT on 27 September 2018 ()
- Where
- 37 km (23 mi) west of Rancho Tehama Reserve, CA · earthquakes near Rancho Tehama Reserve
- Magnitude
- M 1.8 (md)
- Depth
- 10 km below the surface
- Felt
- no reports yet
- Nearest
- Tehama County, 54 km ENE
- Status
- Reviewed by a seismologist
USGS · last changed by USGS · we first saw it 2967 days ago
Earthquake alerts for Rancho Tehama Reserve, CA
Get a notification in this browser when USGS records an earthquake near Rancho Tehama Reserve, 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 9 km (6 mi) from the epicentre. In Rancho Tehama Reserve, 37 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.
How big was it?
This earthquake released about 16 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 5.8 930,000× the energy of this one
- Magna, Utah 2020 M 5.7 660,000× the energy of this one
- Around the size people start to feel M 3.0 59× the energy of this one
- This earthquake M 1.8 about 16 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
No earthquake of M4 or more has been recorded within 50 km since our catalogue begins in 2016.
Before 2016, the USGS record lists one earthquake of M5 or more within 50 km:
- 5.5 33 km NW of Rancho Tehama Reserve, California · 27 km NNE 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 39.9705, -122.8335. Map © OpenStreetMap contributors.
Nearby places
| Place | Distance | Direction from the epicentre | |
|---|---|---|---|
| Tehama County, CA | 54 km (34 mi) | ENE | earthquakes near Tehama County |
| Glenn County, CA | 55 km (34 mi) | SE | earthquakes near Glenn County |
| Trinity County, CA | 79 km (49 mi) | NNW | earthquakes near Trinity County |
| Mendocino County, CA | 79 km (49 mi) | SW | earthquakes near Mendocino County |
| Lake County, CA | 96 km (60 mi) | S | earthquakes near Lake County |
| Colusa County, CA | 102 km (63 mi) | SSE | earthquakes near Colusa County |
Places and coordinates from the US Census Bureau Gazetteer (2024). Distances are from the epicentre.
Aftershocks so far
44 earthquakes have been recorded within 50 km since this one.
- 1.8 36km NE of Covelo, CA
- 2.6 41km S of Hayfork, CA
- 2.7 37km SSE of Hayfork, CA
- 1.5 41km NE of Covelo, CA
- 2.9 15km N of Lake Pillsbury, CA
- 1.9 21km W of Rancho Tehama Reserve, CA
- 1.7 8km ENE of Covelo, CA
- 1.9 19km NNW of Alder Springs, CA
- 1.8 20km NNW of Alder Springs, CA
- 2.4 14km NW of Alder Springs, CA
- 1.8 23km WNW of Alder Springs, CA
- 1.8 16km NW of Alder Springs, CA
- 1.6 24km W of Rancho Tehama Reserve, CA
- 2.3 15km NNE of Alder Springs, CA
- 2.0 14km NNE of Alder Springs, 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.