Slab Geometry and Mountain Building Processes in the Southern Andes

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This research involves the study, by means of PASSCAL portablebroadband seismometers in Argentina and Chile, of the structurebeneath the south central Andes where a major change in subductingslab geometry occurs. The research will be done in conjunctionwith research institutes from Chile, Argentina, France, andGermany. At approximately 33.3 degrees South, the subducting Nazcaslab changes from a horizontal slab geometry without any activevolcanism to the north, to a 30-degree dipping slab with an activevolcanic arc to the south. This north-south change in slab dip isone of the most dramatic bends or warps in a Wadati-Benioff zonegeometry anywhere globally. At 31 degrees South, the flattenedslab extends 300 km to the east before resuming its descent intothe mantle. This segment has high elevations and large amounts oftectonic shortening. Across the dipping slab segment, the elevation decreases, as does the amount of tectonic shortening.Two PASSCAL transects will be deployed: one near 30.5 degrees South above the horizontal slab segment and one at 36 degrees South above the dipping slab segment. The seismic data will be gathered from natural earthquakes and inverted to answer questions involving thestructure of the subducting slab across the transition, surroundingmantle structure, mountain building, and earthquake generationprocesses.