Rapid documentation of earthquake surface displacements using structure from motion photogrammetry

Abstract:

Following the 24 August 2014 Napa earthquake, we used structure from motion (SfM), to produce extremely high-resolution three-dimensional point clouds with mm-scale resolution of surface rupture through anthropogenic features. We show that this method is useful for rapid and inexpensive recording of fault displacement. The SfM technique represents a significant advance over traditional post-earthquake field measurements, which are irreproducible because displacement may change over time due to afterslip, and because the detailed features of a surface rupture quickly degrade either due to weathering or repair. Using SfM, we documented ten sites with tectonic slip along the surface rupture of the South Napa earthquake. Using repeat surveys, we documented two sites with appreciable afterslip over the days, weeks, and months after the earthquake. We illustrate a simple workflow that allows other workers to conduct surveys with enough reference information to easily scale and orient fine scale features of surface rupture captured with SfM.