Joint inversion of high-rate GPS and teleseismic observations for rupture process of the 23 June 2014 (Mw 7.9) Rat Islands archipelago, Alaska, intermediate depth earthquake
Abstract
On 23 June 2014, a large (Mw 7.9) earthquake ruptured within the subducting Pacific plate~ 100km below the Rat Islands archipelago, Alaska. The focal mechanism indicates two possible rupture orientations:(1) on a shallowly dipping fault plane (strike 206, dip 24, rake‐14) striking perpendicular to the trench, possibly related to curvature of the underthrust slab or (2) on a steeply dipping fault plane (strike 309, dip 84, rake‐113) striking parallel to the trench, possibly associated with a slab detachment process. Joint inversion of teleseismic body waves and regional high‐rate (1 Hz) GPS recordings indicate a slip zone spanning 50km× 30km with a maximum slip of~ 11 m on the shallowly dipping plane, or a more distributed slip pattern extending upward to~ 70km, with maximum slip of~ 14 m on the steeply dipping plane. Estimated stress drops are 16 to 25 MPa. The radiated energy is~ 1.8× 1016J, and the inferred low radiation efficiency,~ 0.1, is compatible with the assumed low rupture velocity, 1.5 km/s. The finite‐fault models and aftershocks do not indicate a preferred fault plane. This type of intermediate‐depth intraslab faulting can be very damaging for populated regions above subduction zones such as Japan, Taiwan, Chile, Peru, and Indonesia.