POST-EARTHQUAKE GEOLOGY IN THE ERA OF UBIQUITOUS POINT CLOUDS
Tuesday, 15 December 2015: 11:05
102 (Moscone South)
High-precision 3D imaging with lidar and structure-from-motion photogrammetry is revolutionizing the collection of post-earthquake displacement information. Massive point-cloud datasets, and their differences epoch to epoch, provide valuable information for scientific, engineering, and emergency response, and also pose challenges to process, handle, analyze, share, and visualize. In the physical world, earthquake surface ruptures and secondary deformation features are ephemeral, subject to natural degradation by erosion, or to repair of the built environment. Post-earthquake 3D imaging overcomes this limitation by virtually archiving the primary surface expression of deformation. This allows geologists make precise, repeatable measurements, and to assess subtle, distributed deformation often missed by traditional field methods. Generally, the more local and inexpensive the technique, the quicker that a response can be organized: ground and drone-based SfM (hours), terrestrial laser scanning (days), to airborne lidar (weeks). With the growth of high-resolution topography along fault zones and for other mapping purposes, it is increasingly likely that a large earthquake will coincide with an existing data set. Such an event beholds the exciting promise of point cloud differencing to develop a high-resolution, fully three dimensional displacement and rotation field. Existing paired airborne lidar data sets from Japan, New Zealand, Mexico, and California reveal new and informative features of earthquake-induced near-field deformation, but also illustrate that significant challenges impede the separation a tectonic signal from noise and uncertainty within lidar data. In a future earthquakes, there will be great opportunities, and soon enough, an imperative, to measure deformation at sub-meter resolution over entire cities, and along faults hundreds of kilometers in length. As a community, we stand at a threshold, watching this oncoming deluge of repeat and ubiquitous high resolution topography.