The Role of Fluids in Triggering the 2005 Nias Earthquake Induced by the 2004 Sumatra-Andaman Earthquake
We propose a two-step process to explain the M8.7 rupture as a suspended along-strike migration of the M9.3 rupture. First, the M9.3 earthquake on the plate interface was the initial trigger. Second, it produced a pulse of pore pressure that migrated laterally along the plate interface of the Sunda trench. This pore pressure pulse disturbed the stability of the segment south of the M9.3 rupture, leading to failure of the M8.7 segment. Preliminary numerical results suggest the presence of a fluid-rich permeable subducting oceanic crust sandwiched between the less permeable mantle regions of the down-going slab and overriding wedge. The isolated and permeable oceanic crust favors along-strike migration of excess coseismic pore pressure. This deep lateral migration of pore pressure along the subducting oceanic crust explains the delayed triggering at the hypocenter of the M8.7 earthquake.