Earthquake Preparation for Charleston County: A HAZUS-MH Earthquake Impact Study

The Charleston County Department of Building Services in partnership with the College of Charleston has been using HAZUS-MH to better prepare for the effects of an earthquake in the Charleston region. 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. Although, 137 earthquakes were located in the Charleston region from 1996 through 2003, the risk from a reoccurrence of an earthquake of magnitude 6 or higher within the region is not well known. Recurrence intervals in the region are based on paleo-seismic evidence, thus they are determined based on the relative position of sand blows and crosscutting features found in the soil profiles. Based on this information the recurrence interval of an 1886 style event is estimated to be ~500 years. The recurrence of smaller damaging events in the 5 to 6 magnitude range has not been calculated. Charleston County recognizes that due to changes in land use and population growth the risk to its citizens is now greater during one of these milder earthquakes.

HAZUS-MH is being used by the county to create and implement hazard plans for a variety of earthquake magnitudes. HAZUS-MH has been used to model earthquakes in the region ranging from a repeat of the 1886 event (7.3 magnitude), down to a 4.0 magnitude earthquake. Eight scenarios are being used to design the county's response protocols for potential events in the region. The maps and other HAZUS-MH-based outputs are essential tools for educating the policy makers in the region about their local hazards.