INL Seismic Monitoring Annual Report: January 1, 2011 – December 31, 2011

Payne, S.; Hodges, J.; Berg, R.; Bruhn, D.

During 2011, the Idaho National Laboratory Seismic Monitoring Program evaluated 21,928 independent triggers that included earthquakes from around the world, the western United States, and local region of the Snake River Plain. Seismologists located 2,063 earthquakes and man-made blasts within and near the 161-km (or 100-mile) radius of the Idaho National Laboratory. Of these events, 16 were small-to-moderate size earthquakes ranging in magnitude (M) from 3.0 to 4.4. Within the 161-km radius, the majority of 941 earthquakes (M < 4.4) occurred in the active regions of the Basin and Range Province with only six microearthquakes occurring in the Snake River Plain. In the northern and southeastern Basin and Range, eight earthquake swarms occurred and included over 325 events. Five of the Snake River Plain earthquakes were located within and near the northern and southern ends of the Great Rift volcanic rift zone. The five microearthquakes have anomalously deep focal depths (16 to 38 km) and waveforms indicative of fluid movement at mid- and lower-crustal levels. The 2011 events appear to be a continuation of activity observed at Craters of the Moon National Monument since 2007. During the 39 years of monitoring, the Idaho National Laboratory has recorded 55 small-magnitude microearthquakes (M 2.2) within the eastern Snake River Plain and 25 deep microearthquakes (M 2.3) in the vicinity of Craters of the Moon National Monument.