March 11, 2008

View Map 229 (pdf)

A large (magnitude 7) earthquake occurred about 1,000 years ago near Levan in Juab County and future large earthquakes in this area are possible.

The Utah Geological Survey (UGS) recently released Map 229, “Surficial Geologic Map of the Levan and Fayette Segments of the Wasatch Fault Zone, Juab and Sanpete Counties, Utah.”

The Wasatch fault is Utah’s longest and most geologically active fault, extending more than 200 miles from southeastern Idaho to central Utah. The fault is subdivided into 10 segments; each segment ruptures independently and is a separate source of large earthquakes. The Levan and Fayette segments, extending from Nephi to Fayette, comprise the southern 35 miles of the fault.

The new map completes a series of relatively detailed (1:50,000 scale) geologic maps by the UGS and U.S. Geological Survey that now cover the entire length of the Wasatch fault having evidence for one or more large, surface-faulting earthquakes in recent geologic time (past 10,000 years). The most recent large earthquake on the southern part of the Wasatch fault occurred about 1,000 years ago on the Levan segment.

Geologic mapping of active faults is important in characterizing Utah’s earthquake hazard. The Levan-Fayette map includes a 37-page booklet that provides essential data for a variety of earthquake-hazard parameters including surface-rupture length, vertical ground-surface displacement, prehistoric-earthquake timing, and slip rate.

The map and booklet also provide detailed information about the geologic deposits along the fault zone, some of which are important from the standpoint of geologic hazards. The map can be used as a primary data source from which to generate derivative maps that address a variety of geologic hazards, including surface fault rupture, alluvial-fan flooding, debris flow, landsliding, rock fall, and expansive soil.

Although presently sparsely populated, the proximity of the southern Wasatch fault to the Wasatch Front urban corridor virtually ensures future population growth, so the map can be used as a land-use planning tool before widespread development occurs.