The San Jacinto Fault Zone is, per the USGS, the most seismically active fault in southern California. It is the second major slip-bearing strand of the San Andreas system (after the San Andreas itself), branching off near Cajon Pass and running about 244 km southeast through the Peninsular Ranges into the Imperial Valley. It slips fast — about 12 mm/yr in the north dropping to ~4 mm/yr in the south — and transfers plate-boundary slip from the San Andreas down to the Imperial fault system, passing through the densely populated Inland Empire.
The USGS hazard model splits this fault into 8 sections, each with its own geometry and a geologic slip rate. Each rate says whether it rests on site slip-rate data in the USGS earthquake-geology database or only on the fault’s mapped slip-rate class.
| Section | Movement | Slip rate | Geometry |
|---|---|---|---|
| San Jacinto (Anza) CA | Right-lateral strike-slip | 14 mm/yr (11–18)site data | vertical · 0–17 km deep |
| San Jacinto (Borrego) CA | Right-lateral strike-slip | 5 mm/yr (1–10)site data | vertical · 0–13 km deep |
| San Jacinto (Clark) CA | Right-lateral strike-slip | 8 mm/yr (6–11)site data | vertical · 0–17 km deep |
| San Jacinto (Coyote Creek) CA | Right-lateral strike-slip | 5 mm/yr (1–10)site data | vertical · 0–16 km deep |
| San Jacinto (San Bernardino) CA | Right-lateral strike-slip | 6 mm/yr (2–10)site data | vertical · 0–16 km deep |
| San Jacinto (San Jacinto Valley) CA | Right-lateral strike-slip | 13 mm/yr (13–18)site data | vertical · 0–16 km deep |
| San Jacinto (Superstition Mountain) CA | Right-lateral strike-slip | 7 mm/yr (2–9)rate class only | vertical · 0–12 km deep |
| San Jacinto (stepover) CA | Right-lateral strike-slip | 5 mm/yrrate class only | vertical · 0–16 km deep |
Source: USGS NSHM23 fault sections database v3 and western US geologic deformation model v1.0 (on-plane slip rates, preferred with low–high range; site data = measured sites in the NSHM23 earthquake-geology database, rate class only = the fault’s mapped slip-rate category); central US and Cascadia sources from the model’s source files (code.usgs.gov/ghsc/nshmp/nshms/nshm-conus).
The San Jacinto has produced significant earthquakes in nearly every one of its main sections. It runs through or near the San Bernardino and Riverside metro areas (~4–5 million people), plus Hemet, San Jacinto, Anza, Borrego Springs, and Imperial Valley communities. A June 2026 study reported the southern San Andreas–San Jacinto system at its highest accumulated stress level in about 1,000 years. The USGS models a full multi-segment rupture at M7.8 (San Bernardino Valley + San Jacinto Valley + Anza segments).
A ~20 km section near Anza has had no large earthquake in roughly 200 years while surrounding sections stay active — strain is accumulating. In 2017, UC Riverside researchers detected the first spontaneous tectonic tremor and deep slow slip beneath the gap, which "adds stress to the shallow part" and may ultimately help trigger a damaging earthquake. Paleoseismic work at the Hog Lake site (Rockwell et al., 2015) found 21 surface ruptures in ~4,000 years — an average of about 257 years between large events.
The instrumental record is busy: the 1899 San Jacinto earthquake (M~6.5–6.7, killing 6 at the Soboba reservation), the 1918 Hemet earthquake (M~6.8, 1 death), the 1954 M6.4, the 1968 Borrego Mountain M6.6, and the 1987 Superstition Hills sequence (M6.2 Elmore Ranch + M6.6 Superstition Hills). Recurrence per segment runs roughly 100–300 years. Magnitudes and recurrence figures are estimates and vary between catalogs.
The USGS divides the zone into seven named sections, north to south: San Bernardino, San Jacinto Valley, Anza, Coyote Creek, Borrego Mountain, Superstition Hills, and Superstition Mountain. The principal faults overlap in a right-stepping pattern. Note: the Superstition Mountain and Superstition Hills sections belong to the San Jacinto zone — they are distinct from the parallel Elsinore fault to the southwest. See the Elsinore Fault page.
The San Jacinto's high activity and the Anza gap make it a central concern for the Inland Empire. See the California page and our seismic risk lookup.