a low velocity layer (lvz) at the top of the subducting plate has been detected in a majority of...
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• 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.
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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
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Imag
ing
the
LVZ
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Schematic Model of Hydrologic Evolution
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Possible Interpretations of the LVZ
LVZ = Entire Oceanic Crust
Distributed Shear Zone
SerpentinizedMantle Layer
Fluid-rich Layer within the Overriding
Continental Crust
This Paper: Upper
Oceanic Crust
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Global Survey
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McGary et al., Nature, 2014
Magnetotellurics and Fluid Pathways beneath Volcanoes
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Fluids, Viscosity & Volcanism
Honda and Yoshida, 2005 (modified after Hasegawa and Nakajima, 2004)
Honda & Saito, 2003
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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?
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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??
• …
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