Surface ruptures provide a physically important accessible record of the distribution of slip in earthquakes and are the primary record of prehistoric seismic activity. Traditional field mapping and measurements may incompletely characterize surface ruptures due to their often complex, distributed nature. Prehistoric earthquake ruptures are also subject to surface processes that, over time, smooth out displaced features and mask critical components of the deformation field, such as warping of the land surface.
This grant through the NSF EarthScope Program and the Americas Program of the NSF Office of International Science and Engineering supports the acquisition of very high-resolution airborne LiDAR topography over the surface rupture from the 4 April 2010 El Mayor - Cucapah earthquake in northernmost Baja California. The El Mayor - Cucapah earthquake ruptured the Pescadoros-Borrego fault system, which lies adjacent to the Laguna Salada fault that produced a similar-sized earthquake in 1892. Why the earthquake occurred where it did presents an important challenge to our understanding of the physics of earthquake slip and recurrence. Detailed comparison of the geometry of the 2010 and 1892 surface ruptures, engendered by the airborne LiDAR scan, will be especially important for assessing the relationship between these earthquakes.
The El Mayor - Cucapah Earthquake occurred in a hyper-arid desert setting where little vegetation cover exists to obscure the rupture. Thus high-resolution digital elevation models (~25 cm resolution) may be generated with current scanning technology (>10 points/sq. m), providing very high-resolution measurements of the surface rupture from this earthquake in a near-pristine state. The data span the rupture belt as identified by initial aerial and satellite reconnaissance by at least 500-1000 meters. The data acquisition and analysis involve numerous students and strengthen US-Mexico earthquake science collaborations. Terrestrial laser scanning data covering select portions of the rupture at ultra high resolution (1000s of points/sq. m) will be embedded in the airborne data and their seamless visualization and analysis will be enabled using tools developed at the KeckCaves facility at UC Davis (http://keckcaves.ucdavis.edu/). These data, including the embedded ground-based LiDAR scans, will be made immediately available to the research community using the existing infrastructure of the OpenTopography Facility (www.opentopography.org/). They will significantly advance the state of the art in earthquake geology and address important questions on the nature and preservation of earthquake ground ruptures.
The response to this earthquake enhances international collaboration and education opportunities. Close collaboration with scientists in Mexico has been central to the response to the El Mayor - Cucapah Earthquake. All data-gathering and dissemination activities will emphasize students from both the United States and Mexico. Openly available LiDAR data collected from the ground rupture will provide new opportunities for Mexican scientists and students to work with this imagery data, strengthening new collaborative relationships with U.S. scientists that have been established as part of the earthquake response.
Large continental earthquakes generate complex ruptures. The record of these events in the landscape is often quickly lost due to surface processes. In addition, measuring the subtle effects of the earthquakes in the volume around the causative faults is difficult, yet valuable for contributing to our understanding of the physics of faulting. In this project, we gathered spectacular high resolution topography data using LiDAR technology along the surface rupture of the 2010 El Mayor Cucupah earthquake in northern Baja California. These data sample the topography along the rupture zone at nearly 10 shots per square meter. They depict the rupture in unprecedented detail. The fault traces cut across both alluvial flats and through the steep topography of the mountain range in a discontinuous manner. We documented previously unmapped faults in the Colorado River Delta. When the data are compared with pre-earthquake topographic data, we were able to measure the deformation due to the event along the major faults as well as in the volume adjacent to it. We have learned that the volume adjacent to the fault can sustain significant strains. Without the ability to measure such distributed deformation, scientists may attribute all plate boundary deformation to fault slip. We have also learnt how to plan for future similar acquisitions after earthquakes.
