The Rupture Process of the 2014 Rat Island Intermediate-Depth Earthquake with Relation to the Geodynamical Context of the Western Aleutian Arc

Monday, 15 December 2014
Twardzik Cedric, Chen Ji and Ralph J Archuleta, University of California Santa Barbara, Santa Barbara, CA, United States
The June 2014 (Mw 7.9) Rat Island intermediate-depth (~107 km) earthquake occurs at the junction between the eastern end of the February 1965 (M8.7) Rat Island under-thrusting earthquake and the western end of the 1957 (Mw8.6) Great Aleutian earthquake, where the Aleutian arc intersects with the Bowers Ridge and a change of strike of the subduction zone occurs. We relocate the aftershocks occurring within the first month after the earthquake and combine them with teleseismic P and SH waveforms and long period surface waves together to unravel its slip history. While the inversion cannot distinguish between the two nodal planes derived from its GCMT solution, it is clear that the one with steep dip angle is more consistent with our relocated aftershocks. The preferred fault plane has therefore a strike of 306o and a dip of 84o. The June 2014 (Mw7.9) Rat Island earthquake is an intra-plate oblique normal fault earthquake within the subducted Pacific slab. The inversion leads to a seismic moment of 9.9 x 1021 Nm and an average rupture speed of 2.4 km/s. The slip distribution is separated in two large patches of slip, one east and one west to the hypocenter, with the aftershocks focussing mostly on the western side. The fault orientation also coincides with the orientation suggested for the northern boundary of the Rat block. Consequently, the small right-lateral strike-slip component of the earthquake could be explained by the transmission of the surface rotation of the Rat block at depth. In the meantime, addition of data from one strong-motion station and regional data might help to improve the reliability of the inversion. The possibility of having variable double-couple solutions distributed along strike is also going to be investigated.