Pre-, Syn-, and Post-Seismic Ground Deformation from
Inclusive Dates: 09/15/03 03/15/05
Background - Measurement of ground deformation is extremely important for monitoring active volcanoes, evaluating landslides, glacier movement, land subsidence related to groundwater withdrawal, hydrocarbon production, and underground mining, as well as evaluating fault-related deformation, including earthquakes and surface ruptures associated with fault slip. Assessing deformation rates, including relative movements over large regions and local displacements associated with slip on specific active faults, is increasingly used in earthquake hazard assessment. Interferometric Synthetic Aperture Radar (InSAR) is a relatively new technology that provides spatially dense coverage that has very broad applicability in situations where images were collected before and after the event or period of interest.
Approach - The primary technical objectives of the project were to 1) develop a methodology and technique for creating land displacement maps based on Synthetic Aperture Radar (SAR) images and 2) understand regional deformation that occurs prior to, during, and after seismic (i.e., earthquake generating) fault slip. The radar interferometry technique was applied to a series of image pairs acquired by the European Remote Sensing Satellite (ERS-1 and ERS-2) for an area close to Barstow, California, before and after the 1992 Landers earthquake. InSAR methodology developed in this project could be applied to other events and different types of SAR data, such as that received from the Japanese Earth Resources Satellite (JERS), RADARSAT, and ENVIronment SATellite (ENVISAT).
Accomplishments - We developed expertise in InSAR analysis of ground deformation and developed an improved InSAR technique for generating surface displacement maps and mapping fault ruptures. The developed methodology, based on available SwRI commercial-off-the-shelf and public domain software, has a modular structure that allows future development and customization for a large palette of potential InSAR-related projects.
This project significantly enhanced our ability to use InSAR to map ground ruptures associated with fault slip. Comparison of line-of-sight displacement maps, displacement gradient (slope) maps, and field mapping of ruptures of the Newberry Fracture zone demonstrate the ability to map ground ruptures with displacements on the order of centimeters. Other displacement-gradient anomalies allowed us to identify ground rupture on the Lenwood and Old Woman faults where field observations had suggested minor displacement had occurred, but continuous ground ruptures had not been mapped. These results demonstrate that field mapping and InSAR displacement gradient mapping provide a powerful combination of methods that can improve ground rupture mapping and focus field investigations. We estimated spatial and temporal slip along the Lenwood fault and evaluated long-term (i.e., years) deformation associated with the Landers earthquake. InSAR difference maps illustrate ongoing ground deformation continuing for several years after the Landers earthquake. This result suggests accumulation of permanent deformation that reflects gradual re-equilibration of the regional deformation field after the abrupt perturbation produced by the Landers earthquake.
This project made important contributions toward understanding deformation field perturbations and recovery of the regional deformation field through time. The knowledge gained in this project will advance our capability to simulate deformation fields in tectonically active regions and incorporate geologic information into hazard assessment for sensitive installations such as nuclear waste storage and disposal sites, nuclear power plants, and critical infrastructure in the United States and abroad. The developed InSAR methodology could be used in a variety of other applications dealing with land displacement, such as land subsidence related to oil and gas extraction and groundwater withdrawal, mine collapse, landslides, volcanism, or glacier dynamics. Completion of the project led to an active radar interferometry research program at Southwest Research Institute.