August 28, 2003

A large trench has been excavated to investigate how often large (magnitude 7) earthquakes have occurred in the Provo area over the past 15,000 years to better estimate the likelihood of the next one. URS Corporation of Oakland, California, in cooperation with the Utah Geological Survey, has excavated a “megatrench” in Mapleton along the Provo segment of the Wasatch fault zone.

The trench is called a “megatrench” because it was excavated deeper to expose evidence for earthquakes older than those of the past 5,000 years that have been found in other, shallower trenches in the Provo area. The ultimate goal of the study is to better understand how often large earthquakes occur in the Provo area, how large they are, and how regularly they occur. This information will help scientists evaluate the likelihood of the next large earthquake in the area and calculate the severity of earthquake ground shaking that should be expected in the future.

The trench is up to 30 feet deep and about 300 feet long. Faults exposed in the trench provide direct evidence for possibly 7 large, surface-faulting earthquakes in the past 15,000 years, and indirect evidence for other, older earthquakes.

Those interested in seeing the “megatrench” and hearing the preliminary results are invited to a field review beginning at 10:00 a.m., Monday, September 8, in Mapleton. We will meet at the entrance to the site at 1150 East 1600 South in Mapleton at 10:00 a.m.

To get to the meeting place from 1-15 coming from the north, take the Spanish Fork exit 260 (about 1 mile south of the exit for State Highway 6 to Price). Turn left at the off ramp stoplight onto Main St., proceed south on Main, and then left (east) at the 400 North (Highway 147) stoplight. Proceed east on 400 North, which turns into 1600 South in Mapleton, to the end of the street at the mountain front. We will meet at the locked metal double gate on the south side of 1600 South across from the home at 1155 East (see attached map).

We hope to conclude by 12:00 noon, but can stay as long as needed. Be prepared for heat; bring water, sun protection, and a hard hat if you have one. A limited number of hard hats will be available, and must be worn by those who enter the trench.

This project is funded by a grant from the U.S. Geological Survey National Earthquake Hazard Reduction Program. Susan Olig of URS Corporation (510-874-1729, susan_olig@URSCorp.com) is the principal geologist performing the study and leading the review.

If you have questions concerning the review, contact Gary Christenson (801-537-3304, garychristenson@utah.gov) at the Utah Geological Survey.