Utah Earthquakes (1850–2016) and Quaternary Faults
The Utah Geological Survey (UGS) and the University of Utah Seismograph Stations (UUSS) recently released a 1:500,000 scale ‘Utah Earthquakes (1850-2016) and Quaternary Faults’ map by Steve Bowman (UGS) and Walter J. Arabasz (UUSS). You can download the map at https://ugspub.nr.utah.gov/publications/maps/m-277.pdf
Movement along active faults and the severe ground shaking that accompanies moderate to large magnitude earthquakes provides a substantial hazard to some of Utah’s most densely populated communities. As noted in the map explanation, “The major fault in Utah is the 240-mile-long Wasatch fault zone that extends from north of Malad City, Idaho, south through the Wasatch Front to near Fayette, Utah … .”
According to Steve Bowman, co-author and Program Manager of the UGS Geologic Hazards Program "Due to the 57% probability(over 1 in 2 chance) that a magnitude 6.0 or greater earthquake will occur in the Wasatch Front region in the next 50 years, we developed the map so the public could more fully understand the hazard from earthquakes and faults, as well as the resulting risk to property, infrastructure, and life safety in Utah, and take appropriate action to help protect themselves and their families.
From the Map Explanation: “This map shows earthquakes known to have occurred within and surrounding Utah from 1850 through December 2016 and mapped Quaternary faults considered to be earthquake sources. The faults shown on the map have been sources of large earthquakes (about magnitude 6.5 or greater) during the Quaternary Period (past 2.6 million years) and are the most likely sources of large earthquakes in the future. Most small to moderate size earthquakes plotted on the map are “background” earthquakes not readily associated with known faults and of a size generally below the threshold of surface faulting (about magnitude 6.5). Buried or unmapped secondary faults are likely sources of much of the background seismicity.”
Basin and Range Extension. Quaternary faults and folds in western and central Utah stem from Basin and Range extension that produced a corrugated landscape of alternating sediment-rich basins and mountain ranges demarcated by normal faults. The vast Basin and Range Province includes parts of California, Nevada, Utah, Arizona, New Mexico, Texas, and northern Mexico. By the Early Miocene, ~ 20 million years ago, Basin and Range extension was well underway in western North America.
We congratulate the UGS and their partners on producing and broadcasting this excellent display of the distribution of Quaternary faults and historic earthquake epicenters. The proximity of faults and earthquake epicenters to cities, towns, and villages is clear, as is the hazard and risk of future earthquake activity in Utah.
For an interactive map of Utah’s Quaternary faults, visit https://geology.utah.gov/resources/data-databases/qfaults/ .
AZGS thanks Vicky Clarke (UGS - Publications Manager) for sharing Steve Bowman’s comments.
