Application of high resolution DEM data to detect rock damage from geomorphic signals along the central San Jacinto Fault

We analyze geomorphic properties extracted from LiDAR and SRTM (Shuttle Radar Topography Mission) data to test whether the damage zone along the central San Jacinto Fault (SJF) zone can be resolved with remotely-sensed data in a quantitative fashion. The SJF is one of the most active faults in southern California, with well expressed geomorphology and a fast slip rate, as seen in the geology and by GPS. We use ArcMap and the TauDEM toolbox to compare several morphometric parameters, including drainage density (Dd), on both sides of the fault, using a 1 km and a 5 km buffer for the LiDAR and SRTM data, respectively. We also analyze the spatial patterns of Dd near the fault, using two different definitions of spatial Dd. The high resolution of the LiDAR data allows us to focus on a single fault, eliminating the effects of parallel nearby faults. From the LiDAR data we find that the highest Dd values occur in areas between two fault strands, followed generally by rocks on the northeast side of the fault, with the lowest Dd values occurring on the southwest side of the fault. The SRTM data shows a band of high Dd values centered on the main fault trace with ~ 1 km width. Our results indicate that there is a strong correlation between drainage density and proximity to the fault, with zones of structural complexity along the fault displaying the highest Dd. We interpret this to largely be an effect of degree of rock damage, as these are areas that are expected to be more damaged, and field observations support this contention. If we are correct, then it appears that the northeast side of the SJF is generally more damaged. South of the trifurcation area there is evidence that the signal is reversed on the larger scale, with more damage on the southwest side of the fault inferred from the SRTM data, possibly caused by extension between the Coyote Creek and Clark faults. The implications of the observed asymmetry could be geological evidence for rupture propagation direction, because a preferred propagation direction is predicted to produce asymmetric damage structure that would be recorded in the volume of rock surrounding a fault.