The 23 June 2014 Mw 7.9 Rat Islands archipelago, Alaska, intermediate depth earthquake

Abstract

On 23 June 2014, the largest intermediate depth earthquake (Mw 7.9) of the last 100 years ruptured within the subducting Pacific plate about 100 km below the Rat Islands archipelago of the Western Aleutian Islands, Alaska. The unusual faulting orientation, strike = 206°, dip = 24°, and rake = -14°, is possibly related to curvature of the underthrust slab and high obliquity of the relative plate motions. The first ~15 s of the rupture generated relatively weak seismic waves, followed by strong energy release for the next 25 s. The seismic moment is 1.0 × 1021 Nm, and slip of up to ~10 m is concentrated within a 50 km × 50 km region. The radiated energy is 1.1 to 2.7 × 1016 J, assuming attenuation t∗ of 0.4 to 0.7 s. This type of intraplate faulting can be very damaging for populated regions above subduction zones such as Japan, Taiwan, Chile, and Indonesia. Key Points The 2014 Rat Islands Mw 7.9 earthquake ruptured within the Pacific slabIt is the largest intermediate depth earthquake in 100 yearsThis category of event presents poorly recognized seismic hazard for some zones