Extent of Low‐Angle Normal Slip in the 2010 El Mayor‐Cucapah (Mexico) Earthquake From Differential Lidar

Abstract

We investigate the 4 April 2010 M w 7.2 El Mayor-Cucapah (Mexico) earthquake using three-dimensional surface deformation computed from preevent and postevent airborne lidar topography. By profiling the E-W, N-S, and vertical displacement fields at densely sampled (∼300 m) intervals along the multisegment rupture and computing fault offsets in each component, we map the slip vector along strike. Because the computed slip vectors must lie on the plane of the fault, whose local strike is known, we calculate how fault dip changes along the rupture. A principal goal is to resolve the discrepancy between field-based inferences of widespread low-angle (<30 ∘ ) oblique-normal slip beneath the Sierra Cucapah, and geodetic and/or seismological models which support steeper (50 ∘ -75 ∘ ) faulting in this area. Our results confirm that low-angle slip occurred along a short (∼2 km) stretch of the Paso Superior fault-where the three-dimensional rupture trace is also best fit by gently inclined planes-as well as along shorter (∼1 km) section of the Paso Inferior fault. We also characterize an ∼8-km fault crossing the Puerta accommodation zone as dipping ∼60 ∘ NE with slip of ∼2 m. These results indicate that within the northern Sierra Cucapah, deep-seated rupture of steep faults (resolved by coarse geodetic models) transfers at shallower depths onto low-angle structures. We also observe a statistically significant positive correlation between fault dip and slip, with slip pronounced along steep sections of fault and inhibited along low-angle sections. This highlights the important role of local structural fabric in controlling the surface expression of large earthquakes.

Vertical Coseismic Offsets Derived From High‐Resolution Stereogrammetric DSM Differencing: The 2013 Baluchistan, Pakistan Earthquake

“…Importantly, our vertical offsets support the previously reported observations that the ratio of fault‐parallel to fault‐normal offsets in the 2013 earthquake was at least 6:1 and not smaller than 6:1. While our measurements lead to a broad range of permissible dip values, they further illustrate the strength that 3‐D displacements provide in constraining shallow fault structure (e.g., Ishimura et al, ; Lajoie et al, ).…”

Three‐Dimensional Surface Displacements During the 2016 MW 7.8 Kaikōura Earthquake (New Zealand) From Photogrammetry‐Derived Point Clouds

“…The term offset measurement refers to the motion of one side of a fault relative to the other side of the fault. These coseismic offsets are estimated from cross‐fault swath profiles through the displacement field, similar to previous lidar‐based studies (e.g., Diederichs et al, ; Lajoie et al, ).…”

“…For the part of the Jordan Fault where significant vertical offsets were observed (marked by a box in Figure e), it is possible to constrain the dip of the fault from offset measurements. Elsewhere, vertical offsets are close to zero and rake must be close to 180°; it is impossible to determine the dip of a plane from a purely fault‐parallel slip vector (Lajoie et al, ). The well‐constrained dip estimates at the NE end of the fault cover a relatively large range but are moderate or steep, between ~50 and 80°.…”

“…One obvious comparison to make is between our results and those derived from ICP differencing of lidar point clouds. Several studies have demonstrated that where differential lidar data exist, the ICP algorithm can extract reliable, high-resolution 3-D displacements (Ekhtari & Glennie, 2018;Lajoie et al, 2019;Nissen et al, 2012Nissen et al, , 2014Scott et al, 2018).…”

Distribution of Aseismic Deformation Along the Central San Andreas and Calaveras Faults From Differencing Repeat Airborne Lidar

“…High-resolution imagery and topography from airborne and spaceborne platforms are valuable data sets for measuring coseismic deformation. Differential lidar and optical correlation resolve surface displacements along and adjacent to ruptured faults (Leprince et al, 2007;Nissen et al, 2012;Oskin et al, 2012), measuring on-and off-fault deformation, strain, and shallow fault slip (Lajoie et al, 2019;Milliner et al, 2015;Milliner & Donnellan, 2020;Nissen et al, 2014;Scott et al, 2018Scott et al, , 2019Scott et al, , 2020Vallage et al, 2015;Wedmore et al, 2019). Interferometric Synthetic Aperture Radar (InSAR) provides synoptic creep rate estimates (Lindsey et al, 2014;Tong et al, 2013) but lacks ability to resolve the 3-D deformation field from one or two independent orbits.…”