QuakeIndex

Fault · California

San Juan fault

76 kmlong (47 mi), as mapped
not measuredhow fast it slips
< 15,000 yearssince it last broke the surface
10quakes of M2.5+ within 10 km since 2016

In plain English

Its most recent surface rupture is younger than 15,000 years.

The largest earthquake recorded near it was M 7.9 in 1857 (The 1857 Fort Tejon, California Earthquake) — about 25,000,000 times the energy of an M3.0, the size people start to feel. It released about 12 megatons of TNT.

This week vs. its last ten years

0/100

quiet

0 quakes of M1.5+ within 5 km of the trace in the last 7 days — busier than 0% of weeks since 2016. A normal week: 0–0.

Computed from the USGS catalogue · a description of the past, not a forecast · method

San Andreas faultGreat Valley thrust fault systemHosgri faultLos Osos faultPleito faultWheeler Ridge faultLos Alamos fault M 7.9 · 1857 · The 1857 Fort Tejon, California Earthquake M 6.5 · 1922 · 1922 Parkfield, California Earthquake
The San Juan fault as mapped at the surface (glowing), with the other mapped faults nearby, 10 of the M2.5+ earthquakes within 10 km of it since 2016 (dots), and the epicentres of the large historic earthquakes recorded near it (rings). Traces: USGS Quaternary Fault and Fold Database. Historic epicentres are estimates.

Every year since 2016

Earthquakes of M2.5+ with an epicentre within 10 km of the mapped trace. Near is not the same as on: some will have slipped on neighbouring faults.

The big ones recorded near it

  1. M 7.9 The 1857 Fort Tejon, California Earthquake
    January 9, 1857 · epicentre on the trace
  2. M 6.5 1922 Parkfield, California Earthquake
    March 10, 1922 · epicentre 6 km from the trace

Before 1973 from the USGS ComCat historical catalogue (within 25 km; epicentres of old earthquakes are estimates). Since 2016, M4+ within 10 km.

Most recent near it

  1. M 2.7 3 km ENE of Cholame, CA
    2025-09-11 · 4 km from the trace
  2. M 2.8 16km W of Simmler, CA
    2022-05-05 · 1 km from the trace
  3. M 2.8 8km NNW of Cholame, CA
    2022-01-30 · 8 km from the trace
  4. M 3.0 7km NNW of Cholame, CA
    2022-01-30 · 8 km from the trace
  5. M 3.2 4km NNW of Cholame, CA
    2021-09-28 · 5 km from the trace
  6. M 2.7 7km NNW of Cholame, CA
    2021-07-31 · 8 km from the trace

Neighbouring faults

Fault trace, slip rate and age: USGS Quaternary Fault and Fold Database (public domain), simplified for the web. Earthquakes: USGS ComCat. QuakeIndex does not forecast earthquakes; a fault's history describes the past. For early warning use ShakeAlert.