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What is an earthquake-induced landslide zone?

The hillside counterpart to liquefaction zones: California maps where strong shaking could set slopes moving, and inside those zones new development must investigate the ground before building. If your disclosure packet says 'seismic hazard zone — landslide,' here is what that does and does not mean.

Where the zones come from

After Loma Prieta, the Seismic Hazards Mapping Act (1990) directed the California Geological Survey to map where strong shaking could cause ground failure. The result is one map series with two zone types: liquefaction in the lowlands, and earthquake-induced landslide zones on slopes. CGS combines slope steepness, geologic strength (weak rock and old landslide deposits fare worst), and expected shaking to draw the zones, quadrangle by quadrangle. An old landslide body — of which the Bay Area hills hold thousands — is a strong predictor: ground that has moved before is the ground most likely to move again when shaken.

What the designation does

  • Requires investigation: cities and counties cannot approve most new development inside the zone until a site-specific geotechnical study evaluates the slope and the project incorporates any needed mitigation.
  • Requires disclosure: it is part of statutory item #6 on the Natural Hazard Disclosure (the “seismic hazard zone” box covers both landslide and liquefaction).
  • Does not restrict existing homes — but it hands a hillside buyer the right questions: is there a soils or geology report on file from the original permit? Any history of retaining-wall work, re-leveling, or drainage repairs?

Bay Area context

The zones trace the hills with remarkable fidelity: the Oakland–Berkeley hills (roughly 11% of Oakland and 9% of Berkeley is zoned), the ridge districts of Fremont, and the canyon towns of Marin. The pattern is the mirror image of the liquefaction map — hills versus flats — and many buyers moving “up the hill” to escape one designation are surprised to acquire the other. Every city page shows both percentages side by side.

Reading a hillside listing

Inside the zone, the highest-value document is any prior geologic investigation — newer hillside construction usually has one, and it tells you what the ground under that specific lot is made of. Outside the zone, remember what the boundary means: the mapped earthquake-triggered hazard was judged low, which says nothing about drainage, cut-and-fill grading, or wet-winter behavior. Slopes deserve curiosity regardless of which side of a line they sit on.

Check a specific address: the free sitelume interactive map shows which mapped zones any SF Bay Area address falls in — layer by layer, no sign-up.

Frequently asked questions

Does the zone mean my hillside house will slide in an earthquake?
No. Like its liquefaction sibling, this is a 'zone of required investigation' — slope, geology, and strength conditions make earthquake-triggered sliding plausible enough that new development must study the site first. Whether a specific slope moves depends on the underlying material, groundwater, slope angle, and how the lot was graded — which is exactly what the required investigation determines.
Is this the same as the landslides that happen in wet winters?
No, and this trips people up: the state zones cover earthquake-induced landslides specifically. Rain-driven slides — the debris flows and slumps of atmospheric-river winters — are a related but separately mapped phenomenon (USGS and county susceptibility maps), and a lot that is outside the seismic zone can still have wet-season slope issues. For hillside property, ask about both.
What does the zone require if I build or remodel?
New construction and most significant projects inside the zone need a geotechnical/engineering-geology investigation before permits, with mitigation (retaining structures, drainage, foundation design) where the study finds a hazard. Existing homes are not retroactively affected, but the disclosure follows every sale.
How do liquefaction and landslide zones relate?
Same law (the Seismic Hazards Mapping Act), same maps, opposite terrain: liquefaction zones follow the flat, wet, sandy lowlands; landslide zones follow the steep hillsides. Many Bay Area cities contain both — flatland neighborhoods in one, hill neighborhoods in the other — and a property can be in either, both is rare.

Related reading

Informational summary of publicly available government designations — not legal, insurance, or engineering advice. Zone boundaries and rules change; verify with the issuing agency before making decisions.