Documenting Ancient Wasatch Fault Earthquakes

2/20 (Tuesday)   Documenting Ancient Wasatch Fault Earthquakes    Presented by Alexis Ault, Utah State University.

Utah’s Wasatch Fault is capable of producing major earthquakes throughout the Greater Salt Lake City area and beyond. In order to understand the danger this fault system poses it is important to study what it has done in the past. Geologists commonly trench across fault systems to study them, there are newer high-tech methods that have the potential to significantly increase our ability to understand their history. Thermochronometry is one such technique, it is a tool that enables scientists to use minerals altered along a fault surface by friction-generated heat resulting from an earthquake.

Alexis Ault and her team study hematite, a common mineral in fault zones and present on high gloss “fault mirrors” in the Wasatch fault zone. The friction-generated heat from earthquakes on these fault surfaces is estimated to be >12000C, a temperature which transforms the hematite crystals and causes He loss or “resets” the hematite (U-Th)/He thermochronology system. Her work provides evidence for small-scale earthquakes <4.5 million years ago. These results provide constraints on Utah’s Wasatch Fault rich history, and more importantly should encourage much wider use of these techniques to investigate faults and their associated history of earthquake generation across the globe.