Earthquake · reviewed by a seismologist
M 3.4ml
Earthquake near Castaic, CA
No earthquake was likely felt in Castaic in the 24 hours to 4:53 am PST (12:53 UTC). The last one was M 2.2, 11 km (7 mi) S, at 8:32 am PDT on 18 October 2026, estimated intensity II (weak) in town; 16 felt reports to USGS. Every earthquake near Castaic
This page: a magnitude 3.4 earthquake was recorded 3 km (2 mi) northwest of Castaic, CA, at 12:46 pm PDT on 27 August 2017 (19:46 UTC), 18 km deep. 125 people have reported feeling it to USGS.
USGS: 3km NW of Castaic, CA
58 km (36 mi) NNW of Los Angeles, CA · 16 km (10 mi) NW of Santa Clarita, CA
- When
- 12:46 pm PDT on 27 August 2017 ()
- Where
- 3 km (2 mi) northwest of Castaic, CA · earthquakes near Castaic
- Magnitude
- M 3.4 (ml)
- Depth
- 18 km below the surface
- Felt
- 125 reports · strongest reported intensity IV
- Measured shaking
- intensity IV (ShakeMap)
- Nearest
- Ventura County, 48 km WSW
- Nearest mapped fault
- San Gabriel fault, 2 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 3271 days ago
Earthquake alerts for Castaic, CA
Get a notification in this browser when USGS records an earthquake near Castaic, 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 57 km (35 mi) from the epicentre. In Castaic, 3 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: Valencia 8 km, intensity III · Santa Clarita 16 km, intensity III · Piru 17 km, intensity III · Simi Valley 29 km, intensity II · Moorpark 33 km, intensity II · Agoura 41 km, intensity II · Thousand Oaks 41 km, intensity II · Santa Paula 42 km, intensity II. Estimated for each town centre; each link is that town's own record.
How big was it?
This earthquake released about 2.1 tons of TNT. Magnitude is logarithmic: each whole step up releases about 32 times more energy, so a magnitude 4.4 would have released about 32 times as much.
- Northridge, California 1994 M 6.7 80,000× the energy of this one
- Mineral, Virginia 2011 M 5.8 3,600× the energy of this one
- Magna, Utah 2020 M 5.7 2,500× the energy of this one
- This earthquake M 3.4 about 2.1 tons of TNT
- Around the size people start to feel M 3.0 this one released 4.4× 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 4.1 on 2016-03-12 — about 11 times the energy of this one.
Before 2016, the USGS record lists 19 earthquakes of M5 or more within 50 km; the five largest:
- 6.7 Northridge, California, earthquake · 34 km SSE of this epicentre
- 6.6 1971 San Fernando Earthquake, California · 27 km ESE of this epicentre
- 6.0 Tejon Pass, California · 50 km NNW of this epicentre
- 5.9 1km ENE of Granada Hills, California · 29 km SSE of this epicentre
- 5.8 10km SSW of Agua Dulce, CA · 27 km ESE 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 34.5060, -118.6422. Map © OpenStreetMap contributors.
Nearby places
| Place | Distance | Direction from the epicentre | |
|---|---|---|---|
| Ventura County, CA | 48 km (30 mi) | WSW | earthquakes near Ventura County |
| Los Angeles County, CA | 49 km (30 mi) | SE | earthquakes near Los Angeles County |
| Kern County, CA | 94 km (58 mi) | N | earthquakes near Kern County |
| Orange County, CA | 122 km (76 mi) | SE | earthquakes near Orange County |
Places and coordinates from the US Census Bureau Gazetteer (2024). Distances are from the epicentre.
Aftershocks so far
52 earthquakes have been recorded within 50 km since this one.
- 1.6 3km NW of Frazier Park, CA
- 1.9 4km SW of Sunland, CA
- 1.7 4km WNW of San Fernando, CA
- 1.5 4km S of Frazier Park, CA
- 1.6 4km S of Frazier Park, CA
- 1.9 3km NNW of Frazier Park, CA
- 2.5 4km SE of Piru, CA
- 1.7 3km SSE of Frazier Park, CA
- 1.5 5km WNW of Frazier Park, CA
- 1.6 12km SSW of Agua Dulce, CA
- 2.4 12km SSW of Agua Dulce, CA
- 2.8 16km N of Santa Paula, CA
- 1.5 15km N of Santa Paula, CA
- 2.2 16km N of Santa Paula, CA
- 1.7 15km N of Santa Paula, 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.