March 10, 2008

The Utah Geological Survey (UGS) recently released Special Study 122, "Paleoseismic Reconnaissance of the Sevier Fault, Kane and Garfield Counties, Utah."  The Sevier fault trends north-south through southwestern Utah and northern Arizona, extending from just north of Panguitch, Utah to south of the Grand Canyon in Arizona.  Approximately 67 miles of the 155-mile-long fault are in Utah.

The report shows that while the level of activity is relatively lower along the southern part of the fault, it becomes higher at the fault’s northern end near Panguitch and Bryce Canyon National Park, which receives tens of thousands of visitors every year.

The UGS conducted the study to determine the level of activity of the Sevier fault based on earthquake timing, recurrence, displacement, and vertical slip rate to evaluate the likelihood of large (magnitude 6.5 - 7.5) earthquakes on the fault.  A majority of the data came from near Red Canyon and Black Mountain in Garfield and Kane Counties. 

On the northern portion of the fault, near Red Canyon and Panguitch, the slip rates and surface-faulting recurrence intervals are high compared to the Black Mountain area.  The vertical displacement rates range from 0.05 to 0.38 millimeters per year.  The time intervals between large earthquakes (magnitude 6.5-7.5) range from approximately once every 5,000 to 33,000 years.  Based on more rapid slip rates over the past several thousand years, it appears that large earthquakes have been more frequent in more recent geologic time.

This evidence of geologically recent earthquakes on the northern part of the Sevier fault, places Panguitch and nearby Bryce Canyon National Park in an earthquake hazard area similar to Cedar City, St. George, and other communities that are located near potentially active faults.

Special Study 122 is available for $14.95 at the Natural Resources Map & Bookstore, located at 1594 West North Temple, Salt Lake City (801.537.3320 or 1-888-UTAHMAP; geostore@utah.gov.