This map displays epicenters of selected earthquakes that occurred from November 1984 through December 1989. Only those data that exceed the magnitude threshold for each time period given in Table 1 are plotted. All of the earthquakes presented have magnitudes of 2.0 or greater. Nearly all originated at a depth shallower than 25 km (15 miles).
Symbols are plotted at epicentral locations. Pre-instrumental locations are determined from intensity data. Symbol sizes are scaled into four magnitude ranges. Earthquakes of magnitude 6.0 or greater are labeled with the reference number from Table 2. In addition to these earthquakes, the magnitude 6.1 Pocatello Valley, Idaho, earthquake of March 28, 1975, produced strong shaking in Utah. The epicenter of this shock was several kilometers north of Utah's border within Idaho, at latitude 42°4'N, longitude 112°31'W.
The accuracy of epicentral parameters of earthquakes that occurred since the mid-1970s is greater than that of earlier earthquakes because a major expansion of the University of Utah seismograph network took place at this time. Earthquakes that occurred since 1975 are distinguished on this map from earlier events by the intensity of color of the epicentral symbol, as indicated at left.
