Extent of low‐angle normal slip in the 2010 El Mayor‐Cucapah (Mexico) earthquake from differential lidar

We investigate the 4April2010 M(w)7.2 ElMayor-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 (approximate to 300m) 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 degrees) oblique-normal slip beneath the Sierra Cucapah, and geodetic and/or seismological models which support steeper (50 degrees-75 degrees) faulting in this area. Our results confirm that low-angle slip occurred along a short (approximate to 2km) stretch of the Paso Superior faultwhere the three-dimensional rupture trace is also best fit by gently inclined planesas well as along shorter (approximate to 1km) section of the Paso Inferior fault. We also characterize an approximate to 8-km fault crossing the Puerta accommodation zone as dipping approximate to 60 degrees NE with slip of approximate to 2m. 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.