Use of Enhanced Nehrp Soil Maps for HAZUS-MH Analysis In Charleston SC

Charleston, South Carolina experienced the most damaging earthquake in the Eastern United States. The August 31, 1886 earthquake had an estimated magnitude of 6.9 to 7.3 and was felt over 2.5 million square miles. Earthquake events have been documented in South Carolina since 1698. Seventy percent of these are located in the Middleton Place - Summerville Seismic Zone (MPSSZ), 30 kilometers northwest of downtown Charleston. 137 earthquakes were located in the MPSSZ from 1996 through 2003. The risk from a reoccurrence of an earthquake of magnitude 6 or higher within the region is greater now due to changes in land use and population growth. Major hazards due to ground shaking and liquefaction during an 1886 style event could lead to an estimated 14 billion dollars of damage and potentially 900 fatalities with 45,000 injuries.

HAZUS-MH provides state and local decision makers with a better understanding of the types and magnitudes of the natural hazards. It is dependent on and sensitive to the quality of information that is used to determine the degree of hazards. The Earthquake module in HAZUS-MH requires information derived from the NEHRP (National Earthquake Hazard Reduction Program) soil maps in order to determine the extent of the hazards due to ground shaking and liquefaction. Small changes in the NEHRP soil maps can lead to major differences in the final HAZUS-MH determination and lead to better estimates for emergency managers and planners. This paper looks at the sensitivity of the HAZUS methodology to the resolution and accuracy of the NEHRP soil maps. Additionally, the authors provide a methodology for creating revised NEHRP soils maps for the Charleston Region.