Intraslab rupture triggering megathrust rupture coseismically in the 17 December 2016 Solomon Islands M_w 7.9 earthquake

The 17 December 2016 Solomon Islands earthquake (M_w 7.9) initiated ~103 km deep in the subducting Solomon Sea slab near the junction of the Solomon Islands and New Britain trenches. Most aftershocks are located near the Solomon Islands plate boundary megathrust west of Bougainville, where previous large interplate thrust faulting earthquakes occurred in 1995 (M_w 7.7) and 1971 (M_w 8.0). Teleseismic body wave modeling and aftershock relocations indicate that the initial 30 s of the 2016 rupture occurred over depths of 90 to 120 km on an intraslab fault dipping ~30° to the southwest, almost perpendicular to the dipping slab interface. The next 50 s of rupture took place at depths of 32 to 47 km in the deeper (Domain C) portion of the overlying megathrust fault dipping ~35° to the northeast. High susceptibility to triggering in the region accounts for this compound rupture of two separate fault planes.