Magnitude 3.5 - 185 miles SE of Old Harbor

Tectonic Setting of the Gulf of Alaska

Seismicity of the Gulf of Alaska region is characterized by very shallow earthquake sources confined to the Pacific Plate crust. These events either activate faulting on preexisting fracture zones formed during the ocean ridge spreading processes hundreds of millions of years ago or break along the new fault lines. On January 23, 2018 a magnitude 7.9 earthquake occurred about 200 miles southeast of Kodiak Island. It activated complex faulting on a system of conjugate strike-slip faults. Previously, the 1987 M7.8 and the 1988 M7.7 events were the largest events recorded within the Pacific Plate in the northern Gulf of Alaska region. These were right-lateral strike-slip faulting events that occurred along the north-south-oriented faults.