Seismic Zone

Seismic design procedures in the United States no longer use seismic zones. The Uniform Building Code (1997 and earlier editions) derived seismic design forces from seismic zones, zone factors, near-source factors in Zone 4, and source types. The International Building Code (2000 and later editions) derives seismic design forces from two ground motion parameters (SS and S1), site class, and long-period transition period (TL). Thus, current building codes use seismic design parameters with values that vary continuously across a geographic area, as opposed to zones with distinct geographic boundaries.

None of the seismic design tools on the USGS web site identifies seismic zones.

Specific Building Code Reference Documents

In the United States, a local municipality, or the state in some cases, determines its building code, which is a legal document defining certain characteristics of structures (houses, offices, hospitals, bridges, etc.) built in the municipality. Municipalities often adopt model building codes (for example, the International Building Code or International Residential Code) instead of writing these extensive documents on their own. A municipality can adopt a model building code in full, in part, or with amendments, according to local circumstances. For example, a municipality might adopt the International Building Code, except that a different reference document defines the seismic provisions of its building code.

The USGS does not maintain information about which seismic provisions of building codes are adopted by local municipalities. Engineers and builders who are unsure which reference document governs in their area should contact their local building department before using a seismic design tool on the USGS web site.