2007 Northeast Brooks Range Earthquake Swarm

Mainshock and Aftershocks: 

The Earthquake Center recorded an unusual sequence of earthquakes northeast of Brooks Range in April 2007. The sequence started with a few minor events (magnitude 3+) on April 8th. The largest earthquake (M5.0, large red star) occurred on April 28 at 5:20 UTC (April 27, 9:20 pm ADT). As of the end of April, AEIC have located 75 events in the area (white circles). Four events had magnitudes greater than 4.3 (red stars). Due to sparse seismic network coverage in the area (the nearest station is located 152 miles away), accuracy of the earthquake locations is poor, especially for the smaller events recorded by very few stations.

Felt Reports: 

A few events were felt in Kaktovik, located 37 miles (60 km) NE of the earthquake source area. 

Tectonic Setting: 

Seismicity in this region is characterized by a diffuse zone of activity extending from northeast Brooks Range, across the coastal plane and onto the Beaufort Shelf. Background seismicity is shown by yellow circles, past magnitude 4 and greater earthquakes are indicated by orange stars. In 2006, five magnitude 4+ earthquakes occurred in this general area, with the largest event of M4.6 on February 20, 2006. 

Source Mechanism: 

Focal mechanisms obtained from the waveform modelling for the 2006 and 2007 events are consistent with the left-lateral strike-slip motion along this NE-trending zone of seismicity, i.e. the northeast Brooks Range is moving northward relative to the lowland to the west.