QuakeIndex

quarry blast · reviewed by a seismologist

M 1.5md

Earthquake near Loyola, CA

No: USGS classifies this as a quarry blast, not an earthquake. A magnitude 1.5 quarry blast was recorded 3 km (2 mi) S of Loyola, CA, at 11:23 am PDT on 29 September 2016 (18:23 UTC), less than 1 km deep.

This was on 29 September 2016. The latest near Loyola: M 2.5 on 19 September 2026.

USGS: 2 km S of Loyola, California

26 km (16 mi) W of San Jose, CA · 5 km (3 mi) W of Cupertino, CA

11:23 am PDT, Sep 29, 2016 · · -0.3 km deep · released about 5.9 lb of TNT

10 km30 km60 km120 km N San Mateo County 26 kmSanta Cruz County 36 kmSanta Clara County 38 kmAlameda County 40 kmContra Costa County 67 kmSan Francisco County 93 kmMarin County 99 kmSan Joaquin County 100 kmStanislaus County 101 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
11:23 am PDT on 29 September 2016 ()
Where
3 km (2 mi) S of Loyola, CA · earthquakes near Loyola
Magnitude
M 1.5 (md)
Depth
-0.3 km below the surface
Felt
no reports yet
Nearest
San Mateo County, 26 km WNW
Nearest mapped fault
Monte Vista-Shannon fault, 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 3531 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 10 km (6 mi) from the epicentre. In Loyola, 3 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.

Likely felt in: Loyola 3 km, intensity II · Cupertino 6 km, intensity II · Los Altos 7 km, intensity II · Mountain View 7 km, intensity II · Sunnyvale 8 km, intensity II · Saratoga 10 km, intensity II. Estimated for each town centre; each link is that town's own record.

USGS catalogues this as quarry blast, not an earthquake.

How big was it?

This earthquake released about 5.9 lb of TNT. Magnitude is logarithmic: each whole step up releases about 32 times more energy, so a magnitude 2.5 would have released about 32 times as much.

  1. Mineral, Virginia 2011 M 5.8 2,500,000× the energy of this one
  2. Magna, Utah 2020 M 5.7 1,800,000× the energy of this one
  3. Around the size people start to feel M 3.0 160× the energy of this one
  4. This earthquake M 1.5 about 5.9 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 19 earthquakes of M5 or more within 50 km; the five largest:

  1. 6.9 The 1989 Loma Prieta, California Earthquake · 38 km SSE of this epicentre
  2. 6.5 Near Morgan Hill, California · 48 km ESE of this epicentre
  3. 6.3 16 km SW of Davenport, California · 49 km SSW of this epicentre
  4. 6.2 Near San Jose, California · 27 km E of this epicentre
  5. 6.2 The 1984 Morgan Hill, California Earthquake · 38 km E 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 37.3255, -122.1040. Map © OpenStreetMap contributors.

Nearby places

PlaceDistanceDirection from the epicentre
San Mateo County, CA 26 km (16 mi) WNW earthquakes near San Mateo County
Santa Cruz County, CA 36 km (22 mi) SSE earthquakes near Santa Cruz County
Santa Clara County, CA 38 km (24 mi) ESE earthquakes near Santa Clara County
Alameda County, CA 40 km (25 mi) NNE earthquakes near Alameda County
Contra Costa County, CA 67 km (42 mi) NNE earthquakes near Contra Costa County
San Francisco County, CA 93 km (58 mi) WNW earthquakes near San Francisco 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.

  1. 1.6 2 km NE of Pacifica, California
  2. 2.4 6 km NE of East Foothills, California
  3. 2.1 15 km N of Morgan Hill, California
  4. 1.9 12 km S of Pescadero, California
  5. 1.7 3 km S of Loyola, California
  6. 2.0 8 km E of East Foothills, California
  7. 1.7 2 km S of Loyola, California
  8. 2.3 8 km SE of Livermore, California
  9. 1.7 6 km ESE of East Foothills, California
  10. 2.0 1 km NE of Pacifica, California
  11. 2.3 7 km NNE of East Foothills, California
  12. 1.8 1 km SSW of Loyola, California
  13. 1.5 2 km NE of Pacifica, California
  14. 1.9 10 km N of East Foothills, California
  15. 1.6 3 km S of Loyola, California

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.