Seismic imaging of the interplate boundary and deformation within the overriding Aegean lithosphere
DESCRIPTION: Most of the world's great earthquakes occur at subduction zones, or "megathrusts". These events pose significant earthquake and tsunami hazards to densely populated coastal areas. This project focuses on the Hellenic subduction zone in Eastern Mediterranean, which is the most seismically active region in Europe. This subduction zone presents an apparent paradox in that the megathrust appears to be weakly coupled at present, rupturing in events with maximum magnitudes of ~6, but this system has been capable of producing M>8 tsunamigenic earthquakes in historical time such, as the 365 AD M 8.3 events south of western Crete which is the largest event ever reported in Europe. This project will help resolve this paradox by improving our knowledge of the geometry and properties of the plate interface and other faults in the Hellenic subduction zone. Better constraints on the deep architecture of this subduction zone are essential for assessing hazards for the densely populated Mediterranean coastal regions. The study of the Hellenic subduction zone will also benefit studies of other subduction zones, such as the US Cascadia and Alaska margins. This project involves a strong international collaboration with French and Greek scientists. Funding supports a multichannel seismic survey of the volcanic arc of the Hellenic subduction zone. Acquiring these data takes advantage of a unique opportunity to image the seismogenic part of this subduction zone. The data will be acquired with the deep penetration reflection seismic capabilities of the R/V Marcus Langseth along a 220-km-long profile west of Crete, across the inferred rupture area of the AD 365 earthquake. These data will provide important missing information on the overall geometry of the plate boundary including the thickness of sediment subducting along the plate boundary, interplate roughness and possible downdip variations related to changes in the properties of the interplate, as have been observed elsewhere, allowing a much-improved understanding of the subduction dynamics and processes in this area. The data will be analyzed and interpreted together with co-located ocean bottom seismometer wide-angle reflection-refraction data acquired in 2012 by French partners of this project. Seismicity studies indicate one or more active features in the overriding plate, and some authors recently suggested that past great earthquakes might have occurred on a splay fault rather than on the main plate boundary. The seismic reflection profile will image features in the overriding plate and their relationship to the megathrust and will allow us to distinguish between active faults and relic structures from previous tectonic events. The geometry of these features will provide important constraints on the tsunamigenic potential of these features. In addition to international collaborations, broader impacts include support of an early career female scientist and enhancement of research infrastructure through the first test of the new R/V Marcus Langseth long-offset streamer.