Upper-plate controls on megathrust slip behaviour: Comparing the Hikurangi and Nankai subduction zones

Abstract:

We compare relationships between forearc structure and megathrust slip behaviour along the Hikurangi and Nankai subduction margins. In Hikurangi, active source seismic data recorded by 49 Ocean Bottom Seismographs and a 12.7 km long streamer constrain crustal structure along a 530 km margin-parallel transect. In Nankai, two-decades of onshore-offshore, OBS and passive seismic data have been processed to obtain high-resolution, 3-D constraints on the width and properties of the frontal prism, the thickness and geological architecture of the forearc crust, and the geometry of the subducting Philippine Sea Plate. In Nankai, the geological architecture of Kii Peninsula plays an important role in both the nucleation and segmentation of large megathrust earthquakes. In Nankai and Hikurangi, sharp along-strike transitions in forearc crustal structure are shown to correlate with abrupt and significant changes in the strength of interseismic coupling. We will describe the observations made in Hikurangi and Nankai, their physical and geological interpretation, and the relationships shown with megathrust slip behaviour.