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Hazards, Zoning

Seismic hazards are those related to ground shaking. Landslides, ground cracks, rockfalls, tsunami - these are all seismic hazards. Generally, though, we think more in terms of damage to our structures and our possessions. Engineers, seismologists, architects, and planners have carefully evaluated seismic hazards related to building construction. They have devised a system of classifying seismic hazards on the basis of the expected strength of ground shaking and the probability of the shaking actually occurring within a specified time. The results are included in the Uniform Building Code (UBC) seismic provisions.

The UBC seismic provisions contain six seismic zones, ranging from 0 (no chance of severe ground shaking) to 4 (10% chance of severe shaking in a 50-year interval). The shaking is quantified in terms of g-force (familiar to race car drivers and astronauts), the earth's gravitational acceleration. The diagram below is a way of describing seismic zonation.

Zonation Based on General Principles

In 1992, the USGS was asked to reevaluate the seismic hazards in Hawai`i County. A probabilistic seismic-hazards assessment was carried out according to previously established procedures. eismic-hazards analysis combines:

The new calculations indicate that Hawai`i County has a greater chance of strong ground shaking than was previously thought.

For an overview of seismic hazards in Hawai`i, see the online USGS publication, Volcanic and Seismic Hazards on the Island of Hawai`i, reprinted in 1997.


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Updated : 19 June 2001 (pnf)