HR: 0800h
AN: S51D-1042    [Abstracts]
TI: Earthquake-Induced Ground-Rupture Mapping with InSAR-Derived Displacement Gradiometry
AU: * Ferrill, D A
EM: dferrill@swri.org
AF: Department of Earth, Material, and Planetary Sciences, Southwest Research Institute, 6220 Culebra Road, San Antonio, TX 78238-5166 United States
AU: Necsoiu, M
EM: mnecsoiu@swri.org
AF: Department of Earth, Material, and Planetary Sciences, Southwest Research Institute, 6220 Culebra Road, San Antonio, TX 78238-5166 United States
AU: Smart, K J
EM: ksmart@swri.org
AF: Department of Earth, Material, and Planetary Sciences, Southwest Research Institute, 6220 Culebra Road, San Antonio, TX 78238-5166 United States
AB: Comprehensive maps of active faults and known ground ruptures are critical for the effort to reduce earthquake hazard in seismically active regions such as California. Synthetic Aperture Radar (SAR) data have been collected since the early 1990's by a series of earth-orbiting satellites. Where data quality and character are appropriate, SAR data can be analyzed using interference patterns to determine changes in the ground surface elevation over time (InSAR). Earthquake-related fault slip can generate elevation changes, some of which are transient and some permanent (e.g., ground ruptures). We have developed a refined method of analyzing InSAR data to create displacement gradient maps. Established interferometry methods with phase unwrapping yield maps of line-of-sight displacement, which in turn form the basis for maps of displacement gradients. This refined approach can identify and map displacement field discontinuities that reflect earthquake-induced ground ruptures. The sensitivity and resolution of this approach is demonstrated by application to fault ruptures in the Newberry Springs fracture zone (NSFZ) in the Mojave Valley, California. Comparison of detailed rupture mapping of the NSFZ (based on aerial photographs, field observations and measurements, and InSAR analysis) shows our InSAR-based methodology can identify ground ruptures with displacements of 2 to 10 cm. Applying this method to InSAR data collected for the period bracketing and after the 1992 Landers earthquake provides displacement gradient maps that can be interpreted as detailed surface rupture maps. These maps highlight areas of small-displacement surface ruptures that were detected by traditional means at the time of the earthquake, together with ruptures that were undetected. Although small-displacement ground ruptures may not be intrinsically hazardous, they may be sufficiently significant to be included in seismic hazard assessments. In addition, they can indicate underlying larger and potentially more dangerous faults. This work will lead to improved detection of surface ruptures caused by earthquakes, and a consequent improvement in seismic hazard assessment maps. Further, we hope to find patterns in the ground displacement history that will lead to recognition of faults that are critically stressed and therefore present increased seismic hazard.
DE: 1209 Tectonic deformation (6924)
DE: 1241 Satellite geodesy: technical issues (6994, 7969)
DE: 7215 Earthquake source observations (1240)
DE: 7223 Earthquake interaction, forecasting, and prediction (1217, 1242)
DE: 8123 Dynamics: seismotectonics
SC: Seismology [S]
MN: Fall Meeting 2005