One of the most powerful applications of fault-zone LiDAR scans is to serve as the before image for comparison with a survey acquired after a future surface-rupturing earthquake. Then, every displaced feature acts as a geodetic marker from which an ultra-high resolution map of the surface displacement field may be constructed. Such a detailed displacement field shows how faults and their containing rock volume act together to accommodate deformation and grow geologic structures over successive earthquakes. This provides new understanding of how earthquake ruptures connect faults to generate larger, more destructive events, and illuminates cryptic, distributed components of deformation needed for improving estimates of long-term deformation rates and seismic hazard. This grant through the NSF EarthScope Program and the Americas Program of the NSF Office of International Science and Engineering supports the development of fully 3-dimensional approaches to unraveling deformation from successive airborne LiDAR scans of a fault zone. The focus of the project is the before and after airborne lidar scans of the April 4, 2010 El Mayor-Cucapah (EMC) earthquake rupture in northern Baja California, Mexco. The project objectives address three challenges in working with this data set: (1) reprocessing of the pre-earthquake data to reduce scanning artifacts and improve accuracy; (2) development of methods for rigorous, high-resolution displacement measures from point-cloud data of vastly different resolutions (9 to 18 pts/m2 post-earthquake compared with 0.013 pts/m2 pre-earthquake); (3) preliminary 3-D mechanical modeling of fault-zone deformation from this event. Meeting these challenges will advances knowledge of fault-zone deformation gained from this earthquake, as well as advance techniques for analysis of the next earthquake captured by differential LiDAR -- quite possibly along one of the numerous active faults imaged as part of the Earthscope facility.
Coseismic surface rupture is an important, accessible record of earthquake slip, and the primary record of prehistoric seismicity. Near-field deformation measurements from differential LiDAR can transform our understanding of how coseismic surface ruptures are produced and distributed within fault zones. New knowledge to be gained includes understanding the mechanical coupling of fault slip to near-field distributed deformation, quantifying distributed components of fault slip otherwise difficult to measure, and predicting the style, extent, and magnitude of high strains around fault zones that could damage buildings and critical infrastructure. The techniques developed for this project will also prove valuable for other applications, such as in geomorphology, civil engineering, and robotics. This research brings together the expertise from five U.S.-based research groups that are leaders in the study of differential airborne LiDAR: UC Davis, Arizona State, UC San Diego, University of Houston, and Caltech / USGS. This project also broadens international collaborations formed following the EMC earthquake by involving researchers and students from CICESE, Baja California, in the development and deployment of new differential LiDAR algorithms and the open-source LiDAR-visualization software.
Earthquakes produce complex patterns of permanent ground displacement along fault zones. We have been able to use measures of topography from before and after earthquakes to directly estimate this deformation. To do so, we use methodologies which match pieces of the pre and post earthquake topography and determine what displacement and rotation provides the best match. The measures of topography that we use (and are becoming more and more common globally) are from airborne laser scanning. The resulting point clouds may need refinement and we have recognized the importance of preserving and updating such "legacy" data. We applied our research to the 2010 M7.2 El Mayor Cucupah earthquake which occured in northern Baja California. We used pre event data (2006) from Mexican cartographic agency Instituto Nacional de Estadistica y Geografia (INEGI) and post earthquake data gathered with US National Science Foundation support by the National Center for Airborne Laser Mapping in collaboration with Mexican colleagues at CICESE in Ensenada, Mexico. The differenced topography improved after correction of the 2006 data and we could measure the vertical and horizontal deformation along the rupture belt. In particular, we were able to measure both the discontinuous deformation along the faults, and the more continuous deformation of the intervening blocks. These latter observations are quite valuable because they are otherwise extremely hard to quantify. Intellectual merit: we have been able to measure permanent deformation along faults from single earthquakes at unprecedented fine scales using differential topography. This is complementary to field measurements of fault offsets and remote sensing analysis such as is commonly available from Interferometric Synthetic Aperture Radar or Global Positioning System networks. Broader impacts: We have been able to show the value of topographic differencing made possible by reprocessing of legacy data. We also developed a framework for computing these displacements in future earthquakes in the US as well as applied it to recent earthquakes in Japan. Finally, our international collaboration has strengthened with important scientific and cultural exchange.
