2014 Noatak Earthquake Swarm

Mainshock and Aftershocks: 

A magnitude 5.6 earthquake occurred on Friday, April 18 at 10:44 am AKDT (18:44 UTC) in the western Brooks Range region of Alaska (blue star on the map). It was located 21 km (13 miles) NE of Noatak and 40 km (25 miles) S of the Red Dog Mine site. Nearly 100 aftershocks (blue circles) have been reported through end of April. Five aftershocks had magnitudes of 4.0 or greater. The largest aftershock, magnitude 5.3, occurred at 10:56 am AKDT on April 18, about 12 minutes after the mainshock.

On May 3 at 12:57 am AKDT (8:57 UTC) another moderate earthquake, magnitude 5.5, occurred in the same area (red star). It was followed by a vigourous aftershock sequence (red circles on the map) with 7 events having magnitudes 4 or greater. The two largest aftershocks measured at magnitude 4.7 and occurred about an hour after the mainshock. Only 3 seismic sites are located within 300 mile radius of the earthquake; therefore, only aftershocks with magnitudes ~2.5 and greater can be located.

Felt Reports: 

The mainshocks and largest aftershocks were felt strongly in Noatak and at the Red Dog Mine. It was also felt as far as Kotzebue. No major structural damage has been reported, however some residents reported items falling off the shelves and cracks appearing in the walls and ceilings. Click here [add link] for DYFI map.

Tectonic Setting: 

Seismicity in the region forms diffuse cloud with several clusters. The broad distribution of seismic activity suggests that deformation is distributed over many active structures and not concentrated on a single major fault system. The localized normal faulting may be associated with the formation of pull-apart structures. The April 18 and May 3 events are the largest in the region since the magnitude 5.5 earthquake on 12 July, 1981 (yellow star on the map).

Source Mechanism: 

The elastic-wave radiation pattern of the April and May events indicate normal faulting, typical for this region.