A low velocity layer (LVZ) at the top of the subducting plate has been detected in a majority of subduction zones. LVZ may be a hydrated layer of oceanic.

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Presentation transcript:

A low velocity layer (LVZ) at the top of the subducting plate has been detected in a majority of subduction zones. LVZ may be a hydrated layer of oceanic crust caused by dehydration reactions as the plate subducts. LVZ has interesting consequences for imaging the subduction zone and (potentially) seismogenesis.

Interrogating Shallow Subduction Zone Structure Seismic wave conversions and reverberations Seismic reflection studies Refraction seismic tomography Low velocity wave guides Blue & Red lines bound the LVZ Black line = Oceanic Moho

Imaging the LVZ

Schematic Model of Hydrologic Evolution

Possible Interpretations of the LVZ LVZ = Entire Oceanic Crust Distributed Shear Zone Fluid-rich Layer within the Overriding Continental Crust Serpentinized Mantle Layer Possible Interpretations of the LVZ This Paper: Upper Oceanic Crust

Global Survey

Magnetotellurics and Fluid Pathways beneath Volcanoes McGary et al., Nature, 2014

Fluids, Viscosity & Volcanism Honda & Saito, 2003 Honda and Yoshida, 2005 (modified after Hasegawa and Nakajima, 2004)

Upper Mantle Lower Mantle How are high pore fluid pressures and dehydration reactions related to seismicity (i.e., tremor, Wadati- Benioff zone seismicity)? Along-strike variations? What are the pathways for volatiles and melt in the subduction system and how does this ultimately manifest as surface volcanism? Lower Mantle How do slab fragments contribute to surface magmatism? Why do some slabs bend and stagnate while others penetrate into the deep mantle? What does this mean for material transport?

Subduction Zone Observatory Wish List Upper Mantle How are high pore fluid pressures and dehydration reactions related to seismicity (i.e., tremor, Wadati- Benioff zone seismicity)? Along-strike variations? What are the pathways for volatiles and melt in the subduction system and how does this ultimately manifest as surface volcanism? Lower Mantle How do slab fragments contribute to surface magmatism? Why do some slabs bend and stagnate while others penetrate into the deep mantle? What does this mean for material transport? Subduction Zone Observatory Wish List Ocean Bottom Seismometers Long Running Networks (on land and offshore) Magnetotelluric Surveying Does a subduction zone observatory need to be confined to subduction zones?? …