University of Utah seismograph stations located 168 earthquakes within the Utah region during the fourth quarter of 1990, according to a report prepared for two federal agencies.

Sue J. Nava, senior staff seismologist, says the strongest earthquake recorded during the three-month period was a magnitude 3.2 tremor about 18 miles west of Emery on Oct. 23.Other earthquakes included a magnitude 3.0 shock on Nov. 15, about five miles west of Hiawatha, and a 3.0 earthquake about three miles west of that city on Nov. 21. A magnitude 2.6 quake southeast of Castle Dale on Nov. 20 was felt at Clawson, Ferron and Castle Dale, all in Emery County.

The station also located two clusters of earthquakes near Price, Carbon County, in the magnitude range of 1.5 to 3.0, and three clusters, including 49 earthquakes up to magnitude 2.6 in areas north of the Great Salt Lake.

Nava says the area north of the lake is one of the most seismically active regions in Utah, and the activity in the final three months of 1990 was not unusual. Three swarms of earthquakes north of the lake accounted for a third of the shocks that occurred in Utah during the Oct. 1-Dec. 31, 1990 period.

The Seismograph Stations' quarterly report was prepared with funding provided by the U.S. Geological Survey and the U.S. Bureau of Reclamation.

The U.'s regional seismic network features the operation and centralized recording of more than 80 seismograph stations. The U. facility, operated by the Department of Geology and Geophysics, detects and analyzes about 2,200 seismic events annually. These include distant and regional earthquakes and local blasts.

Since 1974, about 1,100 local earthquakes have been located annually along the Intermountain seismic belt. Of these, about 700 per year occur on average in the Utah region and 500 along the Wasatch Front. The Intermountain seismic belt transects Utah.

Dr. Walter J. Arabasz, research professor of geology and geophysics and station director, says the greatest threat for large surface-faulting earthquakes in the Utah region is posed by the 225-mile long Wasatch fault zone, even though the zone has not generated an earthquake larger than magnitude 5 in historical time.

Since 1850, at least 16 independent earthquakes (aftershocks excluded) of magnitude 6.0 or greater have occurred within the Intermountain seismic belt. Three of these earthquakes were associated with surface faulting - the magnitude 6.6 Hansel Valley earthquake of 1934; the magnitude 7.5 Hebgen Lake, Montana earthquake of 1959; and the magnitude 7.3 Borah Peak, Idaho earthquake of 1983.