Earthquake · reviewed by a seismologist
M 1.7md
Earthquake near Portola, CA
No earthquake was likely felt in Portola in the 24 hours to 1:20 pm PST (21:20 UTC). The last one was M 2.7, 8 km (5 mi) N, at 8:16 am PST on 10 November 2026, estimated intensity III (weak) in town; 9 felt reports to USGS. Every earthquake near Portola
This page: a magnitude 1.7 earthquake was recorded 16 km (10 mi) west of Portola, CA, at 5:23 pm PDT on 27 July 2018 (00:23 UTC), 1.6 km deep.
USGS: 2km N of Plumas Eureka, CA
75 km (46 mi) WNW of Reno, NV
- When
- 5:23 pm PDT on 27 July 2018 ()
- Where
- 16 km (10 mi) west of Portola, CA · earthquakes near Portola
- Magnitude
- M 1.7 (md)
- Depth
- 1.6 km below the surface
- Felt
- no reports yet
- Nearest
- Plumas County, 25 km NW
- Nearest mapped fault
- Mohawk Valley fault, under 1 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 3024 days ago
Earthquake alerts for Portola, CA
Get a notification in this browser when USGS records an earthquake near Portola, 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 12 km (7 mi) from the epicentre. In Portola, 16 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.
Earthquakes near other towns within 30 km: East Quincy, Quincy.
How big was it?
This earthquake released about 10 lb of TNT. Magnitude is logarithmic: each whole step up releases about 32 times more energy, so a magnitude 2.7 would have released about 32 times as much.
- Mineral, Virginia 2011 M 5.8 1,500,000× the energy of this one
- Magna, Utah 2020 M 5.7 1,000,000× the energy of this one
- Around the size people start to feel M 3.0 92× the energy of this one
- This earthquake M 1.7 about 10 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 5 earthquakes of M5 or more within 50 km:
- 5.9 West of Downieville, California · 45 km SW of this epicentre
- 5.6 5 km NE of Loyalton, California · 40 km ESE of this epicentre
- 5.3 11 km N of Soda Springs, California · 47 km SSE of this epicentre
- 5.2 3 km N of Blairsden, California · 3 km E of this epicentre
- 5.0 Nevada County, California · 50 km SSW 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 39.8077, -120.6558. Map © OpenStreetMap contributors.
Nearby places
| Place | Distance | Direction from the epicentre | |
|---|---|---|---|
| Plumas County, CA | 25 km (16 mi) | NW | earthquakes near Plumas County |
| Sierra County, CA | 28 km (17 mi) | SSE | earthquakes near Sierra County |
| Nevada County, CA | 58 km (36 mi) | S | earthquakes near Nevada County |
| Butte County, CA | 83 km (51 mi) | W | earthquakes near Butte County |
| Placer County, CA | 83 km (52 mi) | S | earthquakes near Placer County |
| Yuba County, CA | 84 km (52 mi) | SW | earthquakes near Yuba County |
Places and coordinates from the US Census Bureau Gazetteer (2024). Distances are from the epicentre.
Aftershocks so far
48 earthquakes have been recorded within 50 km since this one.
- 2.2 12km NNE of Little Grass Valley, CA
- 1.6 2 km WNW of Sattley, California
- 1.8 4km ESE of Taylorsville, CA
- 1.7 7km WSW of Greenville, CA
- 1.5 9 km N of Greenhorn, California
- 1.8 9 km NW of Loyalton, California
- 2.2 5km SE of Taylorsville, CA
- 1.8 4km SE of Taylorsville, CA
- 2.9 4km SE of Taylorsville, CA
- 1.8 5km SE of Taylorsville, CA
- 1.6 4 km SSE of Taylorsville, California
- 1.5 9 km S of Taylorsville, California
- 1.7 8 km NNE of Calpine, California
- 2.4 4km SE of Taylorsville, CA
- 2.2 5km SE of Taylorsville, 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.