Seismic Zonation in the New Madrid Seismic Zone

Abstract

Seismic zonation of geologic deposits susceptible to ground motion amplification is implemented by combining in situ measurements, geologic maps, and remote sensing imagery in a geographic information system (GIS). The National Earthquake Hazards Reduction Program (NEHRP) recommends classifying geologic deposits into six profile types based on the average shear wave velocity of the upper 30 meters. Programs such as GIS-HAZUS, created by FEMA, are used to assess seismic risk and estimate potential loss based on the NEHRP classification. Seismic zonation obtained from this project may be incorporated into GIS-HAZUS to improve loss estimates within the New Madrid Seismic Zone (NMSZ). Conventional seismic zonation entails obtaining field measurements of dynamic properties such as shear wave velocity. This approach requires extensive field testing which may not always be cost efficient, particularly in rural areas. Therefore, an approach for identifying soils susceptible to amplification is presented that merges in situ measurements of dynamic properties with geologic information and available remote sensing imagery. Geologic and soil data were used to identify deposits, susceptible to amplification. Remote sensing images were used to delineate alluvial deposits characterized by thick deposits of soft sediments. Geographic information systems (GIS) offer a platform for merging these various data types and assessing the spatial extent of soils susceptible to ground motion amplification. Seismic zonation of the New Madrid Seismic Zone (NMSZ) is currently underway in a cooperative effort with the Association of Central United States Earthquake Consortium (CUSEC) State Geologists and the U.S. Geological Survey. Available in situ measurements of shear wave velocity are continuously being collected and archived for this region. The resulting seismic zonation may be used to identify areas requiring additional field testing.