Geophysical Site Characterization Using Space-Based Imagery and Integrated Imaging Analysis Methods: AN Overview

The identification of active faults and the estimation of local geological site conditions are critical components of seismic hazard assessment. Precise information about regional and local geomorphic and geologic conditions are required to characterize both of these components. In many regions of the world, map information about the character of local terrain is imprecise, sparse, or is not readily available. Because of this, seismic hazard maps for many regions in the world are based on an imprecise assessment of active faults and without consideration of site conditions. We report on our development of methods using high-resolution, multi-spectral, remote sensing data to identify surficial fault features and to provide preliminary site characterizations for estimating ground motions in future earthquakes. Our data sets consist of: 1) optical imagery that include regions in the visible near-infrared (VNIR) through the thermal infrared (TIR) domains, and 2) relative digital elevation models (DEM), based on stereoscopic-correlation methods, derived from NASA's ASTER (Advanced Space-borne Thermal Emission and Reflection Radiometer) sensors. To identify active fault features, we apply edge-detection imaging analysis technology based on contrasts in the luminous intensity in our data. To determine terrain features that control ground motion, we apply automatic object-oriented and pixel-based feature extraction methods on the relative DEM and optical ASTER data, respectively. Using site classification schemes from the Wills et al (2000) and Wills and Clahan (2006) maps of California, we assign Vs30 values for selected regions in California, Afghanistan and Pakistan. Our results demonstrate that detailed site characterization maps, the key basis for microzonation, can be determined from remote-sensing imagery in parts of the world where conventional geological maps are limited or unavailable.