A total of 169 earthquakes were recorded in the state by the University of Utah Seismograph Stations during the last three months of 1991.
Four quakes of 3.0 or greater magnitude on the Richter scale occurred during the period, said Susan J. Nava, senior staff seismologist. The two strongest shocks registered 3.5 magnitude - one Nov. 8, about 28 miles southeast of Vernal, and the other Dec. 21, eight miles east-southeast of Hatch.In its report for the fourth quarter, the seismograph stations noted 25 percent of the quakes in-state during the October-December period struck in active coal-mining areas southwest of Price.
A cluster of 13 temblors up to 1.7 magnitude occurred 45 miles southwest of Logan in the Blue Springs area, approximately the same area hit by a 4.8 quake on July 3, 1989.
A grouping of 17 quakes up to 2.2 magnitude occurred 25 miles southwest of Logan north of the Bear River.
The U.'s seismic network includes more than 80 monitoring stations and analyzes about 2,200 seismic events a year regionally.