Subduction Zone Geodynamics

Abstract

Improvements in the quality and quantity of seismological data, together with technological advances in marine geophysics, mean that we are now able to examine in detail the infl uence of sea fl oor topography on the rupture process of great subduction earthquakes. Subducting seamounts were fi rst suspected to affect the rup- ture process of a great earthquake in the 1986 Mw 8.0 Andreanof Islands earthquake, where large slip was seen in isolated round patches in the direction of the plate subduction. Since then, we have been able to show that a ridge and trough feature on the subducting oceanic plate stalled the rupture process of the 2001 Mw 8.4 Peru for ∼30 s, and then broke, thereby resulting in the third largest earthquake worldwide since the 1960s. An important question is how much of a subducting oceanic plate bathymetric feature remains intact after subduction and how it affects earthquake rupture on the subduction plane. Recent high quality bathymetric and seismic surveys from the Middle America trench, for example, shows both the scars on the hanging wall associated with the subduction of a seamount, as well as large, clear, subducted seamounts after subduction. This paper discusses the rupture histories of four great subduction earthquakes in the Indian and Pacifi c oceans and examines the relation- ships between these histories and bathymetric features on the subducting oceanic plate.