What's really involved in planning and completing a paleoseismology project like this one on the Wasatch fault zone? It's more time-consuming and interesting than you might think.
Selecting and Preparing the Site
The first order of business is selecting a trench site. The trench site location depends on the scientific questions to be answered and the ability to gain permission to dig a trench at the site. In this Wasatch fault zone study, the scientists needed to select site locations that were near the end of known fault segments, so a good bit of staring at maps and wandering around in the field preceded site selection. After a few potential sites are identified, scientists need to get permission from the landowner to dig a paleoseismic trench across the fault; the land may be private property, or owned by the Local, State, or Federal government. Once permission is granted, a detailed topographic survey is completed to record the natural site conditions before any trenching is started.
Now it's time to bring in the excavator and dig the trench. A typical paleoseismology study onthe Wasatch fault zone requires a single trench about 40-50 meters (130-160 feet) long, 5 meters (16 feet) side, and up to 5 meters (16 feet) deep. A trench usually takes one day to excavate, although this time can vary depending on the size of the trench or if more than one trench is excavated.
As soon as the excavator does its job, the paleoseismologists get to work cleaning the walls of the trench, much like archeologists cleaning an archaeological site. They want to make the trench walls as "clean" as possible and to prepare a fresh geologic exposure of the sediment layers and the faults that cut and offset these layers. Preserved in the trench walls is the geologic and tectonic record of paleo-earthquakes at this location along the Wasatch fault zone.