Mobile Laser Scanning Geodesy: a Complement to Space-based Methods

Abstract:

Mobile Laser Scanning (MLS) is an emerging tool that permits autonomous and rapid high-resolution imaging of the surface expression of fault slip. Here, we explore the possibility that MLS geodesy can complement GNSS and InSAR geodetic studies of fault-related deformation. We are particularly interested in transient slip aspects of the earthquake cycle – quasi-continuous creep and post-earthquake afterslip, for example – that have proven elusive to study with other geodetic methods because of their spatially and/or temporally punctuated occurrence. We envision and test two manners of performing MLS geodesy: (1) MLS data referenced to legacy Airborne Laser Scanning (ALS) data sets and (2) MLS data referenced to other MLS data sets collected from a moving automobile. From 2012 to 2014, we collected multiple MLS data sets from a creeping section of Northern California’s Hayward fault near Fremont, CA; the area was also imaged in the 2007 EarthScope regional ALS survey. The study area is a suburban, residential neighborhood and was chosen, in part, so that we could utilize the stability and geometric regularity of built structures as virtual control points in the geodetic analysis. Our analysis derived an estimated offset by a least squares rigid body transformation of planar surfaces from structural features common to each data set. For the ALS-MLS technique this presents a complication because ALS data image mostly house roofs whereas MLS data image a combination of roofs and vertical walls. Using TLS (Terrestrial Laser Scanning) data as ground truth, we find that both ALS-MLS and MLS-MLS techniques have relative accuracy capability of measuring surface fault slip at the ~1cm/yr level. Furthermore, we find good agreement between independently measured creep and the ALS-MLS derived measurement of ~6 cm over 6 years. We discuss the promise of extending this pilot work to cover a much larger portion of the Hayward fault as well as the implications and challenges related to carrying out MLS geodesy in natural environments.