SOURCE FAULT EVALUATION OF THE 1994 DRANEY PEAK EARTHQUAKE SEQUENCE

The Draney Peak Earthquake sequence occurred in southeastern Idaho February 3, 1994 approximately 100 miles east of Pocatello Idaho. It included two initial earthquakes of 4.5 and 5.9 magnitude producing normal fault focal mechanisms. On March 4, 2013 a magnitude 4.0 earthquake occurred in the same area indicating that the region continues to be seismically active. Previous researchers suggest the 1994 events occurred on the Star Valley Fault in Wyoming 17 km east of the hypocenter. The hypocenter depth is ~4.5 km (Brumbaugh, 2001). Using basic trigonometric principles and constraining the dip of the fault to 45 to 60°, the responsible fault should lie approximately 4.5 to 2.6 km from the epicenter. Based on this analysis we hypothesize that the earthquakes occurred on the Meade thrust fault rather than the Star Valley fault. To test the hypothesis, we created a map in ArcGIS using Digital Elevation Models (DEMs) to determine elements indicative of a fault including horizontal offset and linear features. In addition we are using ERS-1 Synthetic Aperture Radar images to create an interferogram of the surface deformation. The results will likely highlight localized vertical displacement caused by the earthquake and show whether surface deformation is consistent with movement on the Star Valley fault or the Meade thrust fault. The earthquakes and the Meade thrust fault lie within the extensional Basin and Range province in the Western United states. The Draney Peak earthquakes may be an instance of reactivation of a Sevier-age thrust fault. Understanding fault reactivation as tectonic stresses shift from compression to extension can increase the ability to predict seismic hazards in the Intermountain West.