Scientific study of the evolution of the southern end of the San Andreas Fault is critical, given the earthquake-prone nature of southern California. To advance this effort, the Department of Geological Sciences at San Diego State Univ. (SDSU) teamed with Geodetics Inc., manufacturer of integrated mobile mapping systems that utilize passive and active vision sensors (LiDAR/Camera), to research the San Andreas Fault in southern California. The study scanned the fault with Geodetics’ drone-based Geo-MMS™ LiDAR/Camera mapping system that uses Velodyne LiDAR technology and an RGB camera to deliver the most accurate 3D data on the market.
The research is focusing on evaluating both past large slip events (earthquakes) and aseismic creep (also known as “silent earthquakes”), which are tremors that release their energy over weeks or months rather than seconds. It is looking to discover new fault zones and active fault traces, which are visible marks where a geological fault meets the ground surface. The research is also looking to detect fault slip that has resulted from past earthquakes.
San Andreas Fault Research
In their study, SDSU researchers are developing a comparison between several techniques for evaluating past slip events and looking to establish precision and accuracy of the techniques relative to each other. Previous work in this area has utilized traditional photogrammetry techniques using small drones to build digital terrain models of earthquake faults.
The Structure from Motion (SfM) approach in photogrammetry to monitor topography changes has been a hot topic in geology for the past two years. However, SfM does not have inherent referencing scale – the scale at which symbols and labels appear on a map at their intended, true size. Other techniques involve LiDAR with the U.S. Geological Service using airborne LiDAR while other researchers have tapped ground-based LiDAR to map topographic expression of the fault and examine offsets, which are the distance the fault is out of line with the map.
The SDSU team used a Geodetics Geo-MMS system including the mapping payload and DJI Matrice M600 Pro drone for its San Andreas Fault mapping. The Geo-MMS payload was equipped with Geodetics’ Point&Pixel™ technology (the Point (provided by the LiDAR) and Pixel (provided by the camera)) which enabled researchers to generate 3D models without the use of ground control points (GCP), which are marked points on the ground that have known geographic locations.