SUBDUCTION SYSTEM STRUCTURE AND FOREARC MORPHOLOGY: CONTROL ON SEISMOGENIC RUPTURE

Improving our understanding of what governs the magnitude, source region and recurrence interval of subduction zone earthquakes constitutes one of the most pressing issues in geosciences today. One of the problems we are facing results from the fact that large parts of the seismogenic zone and forearc are commonly submerged in deep water and difficult to access at the majority of margins. Marine geophysical techniques, which are able to image the complex structures in these settings with sufficient coherency and depth penetration, have evolved in recent years and may thus provide the observational foundation from which to assess the spatial and temporal variation of interplate seismicity. The 2004 Sumatra earthquake sparked many of the questions addressed here: why, along a single convergent margin, do some segments produce large megathrust events whereas other portions of the very same margin only nucleate earthquakes of moderate magnitude? How and why are devastating tsunamis generated in both segments? These observations implicate the notion that individual subduction zones or segments thereof differ in their structure and geometry to induce such diverse behavior. Geophysical imaging shows margin segmentation to be far more complex than previously inferred. The Sunda accretionary wedge was a type-example of 'steady-state' accretion forming a uniform body of imbricate thrusts. However, the newly observed segmentation of structure across-strike correlates to mechanics that vary during an earthquake cycle. Furthermore, the recognition of splay faults and their potential role in tsunami excitation represents an important advance for hazard mitigation efforts. In addition, the impact of lower plate structural diversity on along-strike segmentation is documented. Comparative studies from subduction zones around the globe show the identified structures to be consistent in different margin settings.