HR: 0800h
AN: T41C-0704    [Abstracts]
TI: Tomographic Results From the Nicaragua Subduction Zone: Evidence for a Slab Tear
AU: * Dinc, A N
EM: nilay@geophysik.uni-kiel.de
AF: SFB574, University of Kiel, Department of Geoscience, Otto-Hahn-Platz 1, Kiel, 24118, Germany
AU: Thorwart, M
EM: thorwart@geophysik.uni-kiel.de
AF: SFB574, University of Kiel, Department of Geoscience, Otto-Hahn-Platz 1, Kiel, 24118, Germany
AU: Rabbel, W
EM: rabbel@geophysik.uni-kiel.de
AF: SFB574, University of Kiel, Department of Geoscience, Otto-Hahn-Platz 1, Kiel, 24118, Germany
AU: Flueh, E
EM: eflueh@ifm-geomar.de
AF: IfM-GEOMAR, Wischhofstrasse 1-3, Kiel, 24148, Germany
AB: The Nicaragua convergent margin shows different structures than Costa Rica such as a steeper slab, northward shift in the volcanic front and different geochemical traces in the volcanoes. It is also known as the wettest subduction zone in the world. To have a better understanding of the geometry of the slab and structural changes in the incoming and the overriding plate, local earthquake tomography was performed using 860 local earthquakes recorded by an amphibious network. After iterative simultenous inversion of Vp, Vp/Vs and hypocenters, the cold and dense slab is identified as a high velocity dipping structure anomaly with an angle of approx. 70 deg between depth of 20 - 150 km. Upper parts (0 - 20 km) of the incoming plate (between the trench and coast) and margin wedge show strong low velocity anomalies, which can be explained by eroded thick sediments and serpentinized oceanic crust and mantle due to high amount of fluid infiltration down to several km depths along bend-faults. The slowest mantle velocities are found directly beneath the volcanoes indicating a zone of partial melting extending to 100 - 150 km depth. The most striking observation is the alignment of hypocenters. The Wadati-Benioff zone dips with an angle of approx. 35 deg down to 70 km depth and steepens abruptly to approx. 70 deg below 70 km. An abrupt shift of seismicity towards the trench is observed near the border of Costa Rica and Nicaragua possibly indicating a slab break. This abrupt change is also recognizable in the velocity anomalies laterally correlated with the jump of the volcanic chain towards the trench between Maderas volcano in Nicaragua and Orosi volcano in Costa Rica.
DE: 7240 Subduction zones (1207, 1219, 1240)
DE: 7270 Tomography (6982, 8180)
DE: 8104 Continental margins: convergent
DE: 8170 Subduction zone processes (1031, 3060, 3613, 8413)
DE: 8180 Tomography (6982, 7270)
SC: Tectonophysics [T]
MN: 2007 Fall Meeting