Stress Interactions between an Interplate Thrust Earthquake and an Intraplate Strike-Slip Event: A Case Study of 2018 Mw 7.9 Gulf of Alaska Earthquake

ABSTRACT Most major earthquakes that have occurred in Alaska are related to rupture of the megathrust along the Alaska–Aleutian subduction zone. Large intraplate earthquakes in the oceanic lithosphere are rare. Recently, one large intraplate earthquake occurred near the Alaska subduction zone: the Mw 7.9 Gulf of Alaska earthquake (23 January 2018). The stress interaction between interplate megathrust and intraplate earthquake has been of interest because it helps to understand stress transfer and seismic hazard estimation. To explore the phenomenon of stress transfer, a viscoelastic spherical finite-element-method model accounting for topographic relief and lateral viscosity variations was used to calculate time-dependent stress transfer associated with the 1964 Mw 9.2 Alaska earthquake. We used postseismic Global Positioning System measurements to probe the differences in rheological properties between the continental mantle and oceanic mantle. The best-fitting model determined the viscosities of the continental mantle and oceanic mantle to be 3×1019 and 1×1020 Pa·s, respectively. Then, we calculated the viscoelastic stress transfers based on this viscosity structure. Because of viscoelastic stress loading associated with the 1964 Alaska earthquake, the ΔCFS values on the 2018 Alaska earthquake rupture fault exceeded the threshold (0.01 MPa) for triggering earthquakes.