How long is the Harper fault?

65 km (40 mi) long, as mapped by the USGS Quaternary Fault and Fold Database.

How many earthquakes have been recorded near the Harper fault?

21 earthquakes of M2.5 or more with an epicentre within 10 km of the mapped trace since 2016. Near is not the same as on: some will have slipped on neighbouring faults.

What was the most recent earthquake near the Harper fault?

M 3.2, 33 km SE of Johannesburg, CA, on 2026-04-20, 1 km from the trace.

Fault · California

Harper fault

Q: When did the Harper fault last break the surface?

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

65 kmlong (40 mi), as mapped

not measuredhow fast it slips

< 15,000 yearssince it last broke the surface

21quakes of M2.5+ within 10 km since 2016

Updated April 20, 2026, with the latest earthquake of M2.5 or more within 10 km of the trace: M 3.2, 33 km SE of Johannesburg, CA.

In plain English

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

This week vs. its last ten years

0/100

quiet

No quakes of M1.5+ within 5 km of the trace in the last 7 days. A normal week: 0–0.

Computed 2026-11-13 10:10 UTC from the USGS catalogue · a description of the past, not a forecast · method

The Harper fault as mapped at the surface (glowing), with the other mapped faults nearby and 21 of the M2.5+ earthquakes within 10 km of it since 2016 (dots). 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.

164

172

192

202

211

244

252

264

Most recent near it

M 3.2 33 km SE of Johannesburg, CA
2026-04-20 · 1 km from the trace
M 3.2 18 km ESE of Johannesburg, CA
2026-02-26 · 6 km from the trace
M 3.5 18 km ESE of Johannesburg, CA
2026-02-26 · 6 km from the trace
M 2.5 18 km ESE of Johannesburg, CA
2026-02-09 · 6 km from the trace
M 3.1 16 km NNE of Barstow, CA
2025-02-18 · 10 km from the trace
M 3.5 32 km ENE of Boron, CA
2025-01-23 · 2 km from the trace

Neighbouring faults

Blackwater fault 4 km away
Mt. General fault 6 km away
Lenwood-Lockhart fault 12 km away
Calico-Hidalgo fault 15 km away
Helendale-South Lockhart fault 21 km away
Garlock fault 32 km away

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.