QuakeIndex

Earthquake · reviewed by a seismologist

M 2.5md

Earthquake near Arroyo Grande, CA

No earthquake was likely felt in Arroyo Grande in the 24 hours to 5:33 am PST (13:33 UTC). The last one was M 2.3, 7 km (5 mi) NNW, at 6:27 pm PST on 14 December 2025, estimated intensity II (weak) in town; 25 felt reports to USGS. Every earthquake near Arroyo Grande

This page: a magnitude 2.5 earthquake was recorded 46 km (28 mi) west-southwest of Arroyo Grande, CA, at 8:30 pm PDT on 9 August 2020 (03:30 UTC), 8.2 km deep.

USGS: 40km SW of Avila Beach, CA

53 km (33 mi) W of Santa Maria, CA

8:30 pm PDT, Aug 9, 2020 · · 8.2 km deep · released about 160 lb of TNT

Every earthquake near Arroyo Grande Felt it? Tell USGS Check my area
10 km30 km60 km120 km N San Luis Obispo County 75 kmSanta Barbara County 99 km
Distance rings around the epicentre, with the nearest towns at their true direction and later quakes as coloured dots. Not a shaking map — see the USGS ShakeMap for that.
When
8:30 pm PDT on 9 August 2020 ()
Where
46 km (28 mi) west-southwest of Arroyo Grande, CA · earthquakes near Arroyo Grande
Magnitude
M 2.5 (md)
Depth
8.2 km below the surface
Felt
no reports yet
Nearest
San Luis Obispo County, 75 km NE
Nearest mapped fault
Hosgri fault, 21 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 2213 days ago

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 21 km (13 mi) from the epicentre. In Arroyo Grande, 46 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 160 lb of TNT. Magnitude is logarithmic: each whole step up releases about 32 times more energy, so a magnitude 3.5 would have released about 32 times as much.

  1. Mineral, Virginia 2011 M 5.8 92,000× the energy of this one
  2. Magna, Utah 2020 M 5.7 65,000× the energy of this one
  3. Around the size people start to feel M 3.0 5.8× the energy of this one
  4. This earthquake M 2.5 about 160 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 3 earthquakes of M5 or more within 50 km:

  1. 6.9 The 1927 Lompoc, California Earthquake · 39 km SE of this epicentre
  2. 5.4 77km WSW of Vandenberg Air Force Base, CA · 46 km SW of this epicentre
  3. 5.0 5 km SSW of Nipomo, California · 49 km ENE 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 34.9113, -121.0247. Map © OpenStreetMap contributors.

Nearby places

PlaceDistanceDirection from the epicentre
San Luis Obispo County, CA 75 km (46 mi) NE earthquakes near San Luis Obispo County
Santa Barbara County, CA 99 km (62 mi) ESE earthquakes near Santa Barbara County

Places and coordinates from the US Census Bureau Gazetteer (2024). Distances are from the epicentre.

Aftershocks so far

37 earthquakes have been recorded within 50 km since this one.

  1. 1.6 8 km WSW of Morro Bay, CA
  2. 2.0 34 km WSW of Guadalupe, CA
  3. 2.4 33 km WSW of Vandenberg Air Force Base, CA
  4. 2.0 3 km E of Avila Beach, CA
  5. 1.8 3 km S of Baywood-Los Osos, CA
  6. 2.0 17 km W of Vandenberg Air Force Base, CA
  7. 1.6 22 km SW of Vandenberg Air Force Base, CA
  8. 2.8 5 km W of Baywood-Los Osos, CA
  9. 3.1 8 km NW of Avila Beach, CA
  10. 1.7 8 km NW of Avila Beach, CA
  11. 2.5 12 km WSW of Morro Bay, CA
  12. 1.8 10km W of Orcutt, CA
  13. 1.6 9km SSE of Baywood-Los Osos, CA
  14. 1.8 5km E of Baywood-Los Osos, CA
  15. 1.6 4km ESE of Baywood-Los Osos, 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

QuakeIndex does not issue warnings. For earthquake early warning see ShakeAlert.