MEASURING COSEISMIC SURFACE DEFORMATION WITH DIFFERENTIAL TOPOGRAPHY IN UNDERGRADUATE GEOSCIENCE COURSES

Frequently, the topography surrounding fault zones is measured before and after large earthquakes. Fault scarps are observable in the hillshade imagery produced from the meter to sub-meter scale resolution topographic data. Differencing the before and after earthquake datasets constrains the coseismic surface displacements that occurred both on and off the fault. These displacements are used to identify the type of activated fault (i.e., normal, reverse, strike-slip), measure the slip along the fault plane, assess the deformation in the volumes adjacent to the fault, and determine the earthquake magnitude. In this undergraduate geoscience laboratory exercise, students explore classical faulting relationships, learn about the hazard and scientific response required for large surface rupturing earthquakes, and are exposed to cutting-edge technology for working with topography data.

We develop a laboratory exercise in which undergraduate geoscience students learn about faulting processes by examining coseismic surface ruptures and computing surface displacements from high-resolution topography (<1 m/pix). Students develop a mental scientific model of earthquake processes by mapping surface ruptures and analyzing coseismic surface displacements. Students also gain experience working with digital elevation models, which are increasingly used in geological and engineering applications. This laboratory assignment is designed to be implemented in the active faulting part of a structural geology or geophysics class.

There are four learning goals: (1) Visualize how earthquakes permanently deform landscapes. (2) Describe the relationship between fault slip, surface displacement, and earthquake magnitude. (3) Interpret quantitative geospatial datasets. (4) Practice writing scientific methods and interpretations for an experiment with uncertainty.

In the laboratory assignment, students are given hillshades and point cloud files that represent the surface topography before and after a synthetic earthquake along the Wasatch Fault in Salt Lake City, Utah. They map and describe the surface rupture. They calculate 3D coseismic displacements using the Iterative Closest Point (ICP) algorithm available in Cloud Compare's GUI. Students also determine the type of activated fault and estimate the earthquake magnitude. We will make the course material available on OpenTopography (http://www.opentopography.org).