ANALYSES OF COSEISMIC SURFACE RUPTURE FROM THE 4 APRIL 2010 EL MAYOR-CUCAPAH EARTHQUAKE USING TERRESTRIAL LIDAR

Three high-resolution terrestrial LiDAR (t-LiDAR) datasets collected 12-18 days after the 4 April 2010, M_w7.2 El Mayor-Cucapah earthquake in northern Mexico provide a new opportunity to quantify fresh, meter-scale coseismic surface ruptures and advance understanding of how earthquakes deform the earth’s surface. We map on gridded 3 cm-resolution digital elevation models and analyze the full resolution t-LiDAR point cloud using the KeckCAVES immersive 3D virtual reality space and a 3D-enabled desktop computer. Detailed rupture mapping reveals widely variable rupture styles at three locations. Our mapping suggests that rupture style is dependent on the properties of the material through which a rupture propagates, with more diffuse deformation in less consolidated materials. The surprising extent of centimeter to decimeter scale distributed displacement in some locations raises the possibility that displacements measured across older fault scarps may often be underestimated. Lineations on the vertical fault face measured from full resolution t-LiDAR point-cloud data at two sites define two southeast plunging populations with an average difference in rake of ~30°. The shallower set of lineations (~30° rake) closely matches the ~34° rake of the 2010 slip vector we measured from displaced landforms along the same fault reach. Thus, we conclude that the steeper set of lineations (~55° rake) indicate the slip direction in the penultimate surface-rupturing event. To constrain displacement during the previous earthquake, we reconstructed the pre-rupture topography and collected profiles across a prominent paleo-fault scarp. These profiles yield an average vertical offset of ~3.3 m, from which we estimate an oblique right-normal displacement during the penultimate event of ~4 m along a slip vector plunging ~55° SE. Rapid post-event acquisition of high-resolution terrestrial LiDAR data has allowed us to capture details not only of this most recent surface rupture, but of the penultimate earthquake as well. In addition to serving as a valuable compliment to fieldwork, these data digitally preserve sections of the rupture upon which to base future studies.