New approaches to studying shallow fault zone properties with high-resolution topography

Abstract

Coseismic surface deformation fields provide us with information about the physical and mechanical properties of faults and fault zones. Recent advances in geodetic imaging and analysis allow us to map deformation and infer fault properties at spatial resolutions that were previously unattainable. These high-resolution, remotely-sensed datasets provide an intermediate observational scale that bridges the gap between very local field measurements of surficial faulting and far-field satellite geodesy which samples deeper slip, allowing previously-overlooked shallow-subsurface fault structure to be probed. In this thesis, I use new analytical techniques to study the shallow sub-surface properties of three recent and historic earthquakes that together are representative of diverse, remotely-sensed data types now available. For each earthquake, I (along with co-authors) employ a separate, recently-developed technique that is best suited for the specific dataset(s) involved, and in this way, explore how extant datasets can be analyzed (or re-analyzed) to reveal new characteristics of the earthquakes. The earthquakes studied (which comprise the three chapters of this thesis) are: (1) The 2016 Mw 7.0 Kumamoto, Japan earthquake, for which pre- and post-event gridded digital elevation model (DEM) datasets are available. We compute high-resolution two-dimensional fault offsets along strike using optical pixel tracking on the hillshaded DEMs, and investigate the calculated slip distribution to assess variations in roughness and strain along the rupture and as a function of observation scale. (2) the 2010 Mw 7.2 El Mayor-Cucapah, Mexico earthquake, for which we have both pre- and post-event lidar point cloud data. For this earthquake, full three-dimensional surface displacements are computed using an implementation of the Iterative Closest Point (ICP) algorithm, and fault offsets measured in the resulting x, y, and z displacement surfaces constrain total slip as well as fault dip along strike. (3) The 1992 Mw 7.3 Landers, California earthquake, for which the best existing dataset is a post-earthquake, historical aerial survey. The historical images are used to generate a high-resolution, geo-rectified Structure from Motion (SfM) point cloud. This work serves as a proof-of-concept for a method to study historical earthquakes or remote modern events for which aerial surveys have been undertaken but which lack high resolution topographic data.