Studies on the Source Parameters of the 23 June 2014 Rat Islands, Alaska, MW 7.9 Earthquake Sequence

Abstract

On 23 June 2014, an MW 7.9 earthquake occurred in the Rat Islands region, Alaska, United States. We inverted the full moment tensor for the mainshock, and found the shallow-dip nodal plane (P1) is: strike 207.4°, dip 27.1°, slip −12.7°; the steep-dip plane (P2) is: strike 308.7°, dip 84.2°, slip −116.5°. The larger aftershocks that have depth phase records were relocated and found the majority were distributed along a moderate dipping trend. The steep-dip plane was selected as the causative plane. Using the steep-dip plane as the rupture plane, source rupture process inversions were performed. The obtained maximum slip was about 3.5 m. The optimal rupture velocity VR was about 2.0 km/s. The shallow-dip plane was also used as a rupture plane to perform rupture inversion trials. Curiously the overall waveform fit between the observed and the synthetic seismograms is slightly better than that when the steep-dip plane was used. The catalogue hypocenters of the aftershocks with magnitude ≥ 4.0 were used to simulate a spatial plane. The simulated plane is moderate dipping towards north-west. When the simulated plane was used as the rupture plane, the overall waveform fit was poor. The moderate dipping plane was not the causative plane.