Undergrad Faulting Lab

Measuring coseismic deformation with differential topography in undergraduate courses

When a fault ruptures the surface in an earthquake, the fault scarp is observable in a topographic hillshade produced from meter to sub-meter scale resolution imagery. Frequently, earthquakes are now imaged by before and after topography. Differencing these two datasets constrains on- and off- fault surface displacements. These displacements are used by scientists to identify the type of activated fault (i.e., normal, reverse, strike-slip), measure the amount of slip on the fault plane, assess the deformation in the volumes adjacent to the major fault, and determine the earthquake magnitude. In this laboratory exercise, students explore classical faulting relationships and are exposed to cutting-edge technology.

We develop a laboratory exercise in which undergraduate students learn about faulting processes by examining coseismic surface ruptures and computing surface displacements from high-resolution topography (<1 m/pix). Students develop their 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 used in increasingly more 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) Students visualize how earthquakes permanently deform landscapes. (2) Students describe the relationship between fault slip, surface displacement, and earthquake magnitude. (3) Students interpret quantitative geospatial datasets. (4) Students 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 an earthquake. They map and describe surface ruptures. They calculate 3D coseismic displacements using the Iterative Closest Point (ICP) algorithm available in Cloud Compare's GUI. Students determine the type of activated fault and estimate the earthquake magnitude.