INL Seismic Monitoring Annual Report: January 1, 2005 - December 31, 2005

Abstract

During 2005, the Idaho National Laboratory (INL) recorded 2390 independent triggers from earthquakes both within the region and from around the world. 38 small to moderate size earthquakes ranging in magnitude from 3.0 to 5.7 occurred within and outside the 161-km (100-mile) radius of INL. Earthquakes activity occurred in areas that have experienced seismic activity in the past, the Basin and Range northwest of the INL, southwestern Montana, Yellowstone Park, Wyoming, Jackson, Wyoming, and southeastern Idaho. INL recorded the July 26, 2005 body-wave magnitude (mb) 5.7 Dillon, Montana earthquake and 100’s of associated aftershocks. Local residents felt the earthquake and experienced minor damage. The mb 5.7 main shock was located more than 170 km (105 miles) from INL facilities and was not felt. The main shock did not trigger any strong-motion accelerographs (SMAs) located within INL buildings. Free-field SMAs and accelerometers co-located with seismic stations recorded acceleration data. Peak horizontal and vertical accelerations range from 0.0077 to 0.0006 g. There were 449 earthquakes with magnitudes up to 4.6 that occurred within the 161-km radius of the INL in the Basin and Range surrounding the eastern Snake River Plain (ESRP). No earthquakes occurred within the INL boundaries or the ESRP. The largest earthquake occurred on October 31, 2005 and had a moment magnitude (Mw) 4.6. It was located north of Leadore, Idaho at a distance of 100 km (62 miles) from INL. The earthquake did not trigger SMAs located within INL buildings. Free-field SMAs and accelerometers co-located at seismic stations recorded peak horizontal and vertical accelerations that ranged from 0.0003 to 0.0030 g.