QuakeIndex

Earthquake · reviewed by a seismologist

M 1.6md

Earthquake near Boulder Creek, CA

No earthquake was likely felt in Boulder Creek in the 24 hours to 3:35 am PST (11:35 UTC). The last one was M 2.3, 12 km (7 mi) E, at 2:58 am PDT on 9 October 2026, estimated intensity II (weak) in town; 3 felt reports to USGS. Every earthquake near Boulder Creek

This page: a magnitude 1.6 earthquake was recorded 8 km (5 mi) north of Boulder Creek, CA, at 9:23 am PDT on 27 June 2018 (16:23 UTC), 13 km deep.

USGS: 8km N of Boulder Creek, CA

29 km (18 mi) WSW of San Jose, CA · 15 km (9 mi) SSW of Cupertino, CA

9:23 am PDT, Jun 27, 2018 · · 13 km deep · released about 7.1 lb of TNT

10 km30 km60 km120 km N Santa Cruz County 23 kmSan Mateo County 33 kmSanta Clara County 39 kmAlameda County 53 kmContra Costa County 82 kmSan Francisco County 100 kmStanislaus County 107 kmMarin County 110 kmSan Joaquin County 111 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
9:23 am PDT on 27 June 2018 ()
Where
8 km (5 mi) north of Boulder Creek, CA · earthquakes near Boulder Creek
Magnitude
M 1.6 (md)
Depth
13 km below the surface
Felt
no reports yet
Nearest
Santa Cruz County, 23 km SSE
Nearest mapped fault
Butano 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 3060 days ago

This was a minor earthquake. Quakes this small are rarely felt and do not cause damage.

At this magnitude and depth it was probably too small to be felt, even directly above it. In Boulder Creek, 8 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: Brookdale, Saratoga, Lompico, Monte Sereno, Ben Lomond, Los Gatos.

How big was it?

This earthquake released about 7.1 lb of TNT. Magnitude is logarithmic: each whole step up releases about 32 times more energy, so a magnitude 2.6 would have released about 32 times as much.

  1. Mineral, Virginia 2011 M 5.8 2,100,000× the energy of this one
  2. Magna, Utah 2020 M 5.7 1,500,000× the energy of this one
  3. Around the size people start to feel M 3.0 130× the energy of this one
  4. This earthquake M 1.6 about 7.1 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

The largest earthquake within 50 km since 2016 was M 4.1 on 2017-10-10 — about 5,800 times the energy of this one.

Before 2016, the USGS record lists 24 earthquakes of M5 or more within 50 km; the five largest:

  1. 6.9 The 1989 Loma Prieta, California Earthquake · 28 km SE of this epicentre
  2. 6.5 Near Morgan Hill, California · 44 km ESE of this epicentre
  3. 6.3 22 km S of Davenport, California · 44 km S of this epicentre
  4. 6.3 16 km SW of Davenport, California · 36 km SSW of this epicentre
  5. 6.2 Near San Jose, California · 31 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 37.1972, -122.1237. Map © OpenStreetMap contributors.

Nearby places

PlaceDistanceDirection from the epicentre
Santa Cruz County, CA 23 km (14 mi) SSE earthquakes near Santa Cruz County
San Mateo County, CA 33 km (20 mi) NW earthquakes near San Mateo County
Santa Clara County, CA 39 km (24 mi) E earthquakes near Santa Clara County
Alameda County, CA 53 km (33 mi) NNE earthquakes near Alameda County
Contra Costa County, CA 82 km (51 mi) N earthquakes near Contra Costa County
San Francisco County, CA 100 km (62 mi) NW earthquakes near San Francisco County

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

Aftershocks so far

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

  1. 1.7 4km SSW of Los Altos Hills, CA
  2. 1.9 18km WNW of Bonny Doon, CA
  3. 2.2 18km WNW of Bonny Doon, CA
  4. 2.1 15km E of Seven Trees, CA
  5. 1.9 11km SSE of Portola Valley, CA
  6. 2.7 8km ENE of Alum Rock, CA
  7. 2.2 18km WNW of Bonny Doon, CA
  8. 1.5 3km S of Loyola, CA
  9. 2.5 9km E of Alum Rock, CA
  10. 1.6 18km WNW of Bonny Doon, CA
  11. 2.8 15km ENE of Alum Rock, CA
  12. 1.8 7km ENE of Morgan Hill, CA
  13. 1.5 7km SSE of Portola Valley, CA
  14. 1.8 7km SSE of Portola Valley, CA
  15. 2.1 15km S of Bonny Doon, 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.