The role of the Investigator Fracture Zone in the Sumatra subduction zone process using high-resolution bathymetry, seismic data and numerical geodynamic models
IPGP - Îlot Cuvier
Soutenances de thèses
Géosciences marines (LGM)
Great earthquakes occur mainly on subduction plate boundaries, but what causes the along strike earthquake segmentation remains poorly understood. To understand earthquake segmentation, I have processed, analysed and interpreted high-resolution seismic reflection and multibeam bathymetry data acquired during the MegaTera experiment of 2015. The MegaTera survey covered an area where the Investigator Fracture Zone (IFZ), a linear group of long ridges, impinges the trench along the central Sumatra subduction zone. The interpretation results show the subduction of these four groups of ridges has a considerable impact on the accretionary wedge morphology, including strike-slip and normal faulting, along with thrusts, leading to the development of complex channel systems and basins, and hence erosion. The relief of IFZ ridges has uplifted the forearc sediments, creating subsidence in the wake of subducting ridges. Frontal parts of the subducting ridges have created long-lived thrusts, whereas the décollement horizontally passes through the sedimentary sequences on the top of two neighbouring ridges. Additionally, I have performed 3-D numerical geodynamic models to study the effects of oblique subduction of ridges on the persistent stress evolution and the permanent forearc deformation patterns. Finally, I have analysed and compared the numerical experiments to the interpretation of the seafloor and subsurface features. The overall results indicate the subducting IFZ create heterogeneous wedge deformation and stress behaviour along the accretionary prism. Hence, the subduction of the IFZ might promote a heterogeneous inter-plate coupling, acting as a segment boundary and being a proper candidate for having stopped the south-eastward propagation of the 2005 Mw 8.7 Nias-Simeulue earthquake.