QuakeIndex

Fault · California

West Napa fault

43 kmlong (27 mi), as mapped
0.2–1 mm/yrhow fast it slips
last 150 yearssince it last broke the surface
21quakes of M2.5+ within 10 km since 2016

In plain English

The two sides move 0.2 to 1 mm a year — 2 to 10 cm every century.

It has broken the ground surface within the last 150 years.

The largest earthquake recorded near it was M 6.4 in 1898 (South of Sonoma, California) — about 130,000 times the energy of an M3.0, the size people start to feel. It released about 60 kilotons of TNT.

USGS maps it as 2 sections: Browns Valley section, Napa County Airport section.

This week vs. its last ten years

97/100

unusual

2 quakes of M1.5+ within 5 km of the trace in the last 7 days — busier than 97% 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 systemSan Gregorio faultBartlett Springs fault systemMaacama faultCalaveras faultHayward faultGreenville faultHunting Creek-Berryessa fault systemRodgers Creek faultBennett Valley faultGreen Valley faultAlexander-Redwood Hill faultKonocti Bay faultConcord faultPleasanton faultCordelia faultBig Valley faultSerra faultCorral Hollow-Carnegie fault M 6.4 · 1898 · South of Sonoma, California
The West Napa fault as mapped at the surface (glowing), with the other mapped faults nearby, 21 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 6.4 South of Sonoma, California
    March 31, 1898 · epicentre 16 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 2.5 0 km NNW of Angwin, CA
    2026-07-07 · 9 km from the trace
  2. M 3.6 0 km W of Angwin, CA
    2026-07-07 · 9 km from the trace
  3. M 2.7 7 km SSW of Yountville, CA
    2025-08-21 · 3 km from the trace
  4. M 2.6 6 km WNW of Yountville, CA
    2025-04-29 · 2 km from the trace
  5. M 2.6 3 km ENE of Saint Helena, CA
    2024-12-16 · 4 km from the trace
  6. M 2.5 3 km ENE of Saint Helena, CA
    2024-10-05 · 5 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.