Temperature distribution for interplate seismic events in the southcentral Alaska subduction zone based on 3-D thermomechanical modeling

Abstract

In the southcentral Alaska subduction zone, the Pacific plate and an oceanic plateau, known as the Yakutat terrane, are subducting at a convergence rate of ∼4.7 cm/yr in the direction of N21.5°W with respect to the current North American plate. We constructed a 3-D thermomechanical model to simulate the simultaneous subduction of the Pacific plate and Yakutat terrane. In the numerical simulation, the oceanic plate subducts along a 3-D geometry model obtained from the seismic data, with a spatiotemporally changing convergence rate that was provided based on the past plate motion model. Under these conditions, we obtained the time-dependent temperature and mantle flow velocity fields from 18 Ma to the present. As a result, we discovered that the interplate temperature for the source region of the 1964 Alaska earthquake with a coseismic slip larger than 2 m was estimated to be 155–323 °C at depths of approximately 10–20 km. We also estimated the temperature for the slip area with cumulative slip larger than 5 cm of the northeastern 2009–2013 long-term slow slip event (L-SSE) and the southwestern 2010–2012 L-SSE to be 337–570 °C and 300–381 °C, respectively. In the southcentral Alaska subduction zone, the temperature at the boundary between the downdip of the seismogenic zone and the updip of the L-SSEs is estimated to be approximately 350 °C, which is consistent with the temperature at the transition from frictional instability to stability at the plate boundary proposed in previous studies.