Show 1 f Earthquake hits NW Uintah Basin Friday morning morning An earthquake registering between 45 and 50 on the Richter scale shook the northwestern nor nor- Uintah h Basin in the pre-dawn pre hours of Sept September 30 The location and magnitude was first reported by the US U.S. Geological Survey earthquake monitoring station at Boulder Colorado and was later tater confirmed confirmed confirmed con con- firmed by the University UniVE lly of Utah Seismological Station Dr Walter J J. J Arabasz Research Associate Professor of Geology and Geophysics University of Utah said the U of ofU ofU ofU U seismograph station has determined a Richter r r r magnitude of 44 for the shock with a revised epicenter at 40 deg 30 north deg 38 west 26 miles mile NW of Duchesne Duchene and about 9 miles mites SW of Moon Lake Current field studies studie include the operation of 12 portable seismographs in the earthquake area to study small continuing after shocks and an evaluation of ground motion and possible damage related to the main shock No personal injury or serious property damage has yet been related to the main shock However many any people in Duchesne and Uintah counties felt fell the quake Stated Dr Arabasz most residents in Mountain Home the town nearest the epicenter were awakened by what they described as a sharp jolt Several elk hunters camped in inthe inthe inthe the Moon Lake area reported being awakened and vigorously by the strong motion Some minor rock falls were observed in the Rock Creek Canyon area that were possibly caused by the shake Also a cracked window in a cabin was reported in that area THE EARTHQUAKE took place southwest of Moon Lake Duchesne County in an area which has been generally considered stable and free of seismic activity However in recent years detailed geologic mapping and careful field examinations in the Uintah Basin by the Utah Geological and Mineral Survey have revealed subtle but definite indications of seismic activity of relatively recent geologic age The recent tremor seems to be a continuation of these earth movements Howard Assistant Director of the Utah Geological and Mineral Survey and specialist on the structure of the Uinta Mountains stated The are bordered north and south by very large folds and faults which give rise to much of the sharp ridge and valley topography of the Uinta Vinta foothills This structure so spectacular in the Flaming Gorge and Dinosaur Monument areas is mostly concealed along the south flank of the from Whiterocks River to west west Est of the Duchesne p chesne River These structures took shape 30 to 40 million years ago but have been inactive since that time lime However there are a number of lines of fracturing and faulting separate from the that trend east east- northeast to west-southwest west along the south flank of the mountains and extend out into the basin to the south These apparently reflect a very ancient ancient ancient an an- seated deep rupture in inthe inthe inthe the crust of the Earth that can be traced from the northeast corner of Utah westward nearly to the Nevada line This line Is older than the and apparently apparently apparently ap ap- is still active to some extent The September 30 earthquake occurred along this line lineament in the area are southwest of Moon Lake Mr explained that the lineament along which the earthquake occurred has very subtle but definite expression including lines of springs sinkholes and caves disturbed drainage lines landslide areas and md in some places fault scarps with wilh Indications of movement since the end of glacial time perhaps as recent as to a few hundred years One such area noted by Mr is Flat four miles northwest of Mountain MountainHome MountainHome MountainHome Home where well defined fault scarps cut a glacial plain Mr has named the regional line of fracturing and faulting Lineament for these excellent exposures The faults displayed here said Mr are equal in magnitude and as fresh fresh- appearing as any faults exposed along the Wasatch Front Other areas where faulting is displayed are near the head of Wagstaff Hollow southeast of Tabiona north of Little Valley northeast of Tabiona southeast of Twin vin Pots Reservoir and in inthe inthe inthe the Big Tom Hollow area east of the Whiterocks River Fracturing Frac Frac- turing luring and faulting associated with the Lineament also appears to exert control on the location of several mineralized areas and tar sand deposits and may influence the productive fracture pattern of the Greater Bluebell Altamont oil field Kenneth L. L Cook Professor of Geophysics University of Utah Seismograph Station is conducting conducting conducting con con- ducting a study of the ground motion in the recent e earthquake by asking people in the area of the quake to fill out the questionnaire and mail it to him Results of the survey will be published in the Vernal Express |