JCP Reports - What Types of Geologic Hazard Information Exist?

What Types of Geologic Hazard Information Exist?

By JCP Geologists

Since the earthquakes on October 17, 1989, and January 17, 1994, many buyers have become more sensitive to the ground under their feet. They may have questions regarding faults, bedrock, geology etc. before purchasing a home. The following is a short summary of some of the geologic information developed for disclosure purposes and for helping answer questions:

Alquist-Priolo Earthquake Fault Zones

Alquist-Priolo Earthquake Fault Zones are zones at least 600 feet wide on both sides of active faults. Property within these zones has a relatively higher risk of fault rupture (ground fracturing along the fault plane during an earthquake). Disclosure is state mandated for properties that are within or partially within these zones. Earthquake shaking can be as strong or stronger close to and outside a State Special Studies Zones as within it depending on the local geology.

Seismic Hazards Mapping Act

Early in October 1996, a set of Preliminary Seismic Hazard Maps was published for California by the California Department of Conservation. These maps show areas susceptible to liquefaction and earthquake triggered slope instability. For further information see the California Division of Mines & Geology Home Page.

Seismic Safety Elements

California has mandated that all counties and cities address geologic hazards in their General Plans. This is called the "Seismic Safety Element" of the General Plan. These may address such geologic hazards as ground shaking potential, landslides, slope stability, faults etc. within the jurisdiction. This information is often placed on maps to delineate areas of various geologic hazards. Some counties and cities such as Santa Clara County and the city of San Jose mandate geologic disclosure from their Seismic Safety Elements. More and more counties and cities are adopting maps delineating natural hazards in their general plans. Although not always mandatory, when these maps are publicly available it is prudent to include this local disclosure.

Local Planning Department

The local city or county planning department may have information such as soils reports, permits, geologic reports etc. for an individual parcel.

A JCP Natural Hazard Disclosure Report provides accurate information on Earthquake Fault Zones, Seismic Hazard Mapping Act Zones and Seismic Safety Elements, as well as National Flood Insurance Program Flood Zones, Dam Innundation Zones, Very High Fire Hazard Severity Zones (Bates Zones) and State Fire Responsibility Areas. The JCP Report also includes local county and city level information where available.