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Poster
DDC:
550 - Earth sciences
Abstract:
The central Andes are characterized by significant along-strike variations in magmatism, upper crustal shortening, crustal thickness, and lithospheric structure. Higher resolution regional-scale tomographic imaging of the upper mantle, including the subducting slab and the mantle below it, is required to better understand the relationship between large-scale structural variations and mountain building processes. Multiple temporary seismic networks composed of both broadband and short period stations have been deployed in the central Andes between ~16 to 26°S. The goal of this project is to integrate data from the individual seismic networks in the study region between 1994 and 2008 into a single database and, using modern teleseismic tomography methods, study variations in the upper mantle to depths of ~600 km. P-wave arrivals for teleseismic events between 30° and 90° in three frequency bands (0.2 to 0.8 Hz, 0.1 to 0.4 Hz, and 0.04 to 0.16 Hz) are picked for the broadband stations using a multi-channel cross-correlation algorithm. A single frequency band (0.5 to 1.5 Hz) is picked for the short period stations to help increase the resolution in the study area. Initial results from finite frequency tomography inversions clearly show a trench-parallel fast anomaly with around +2% velocity perturbation. This anomaly migrates to the east with increasing depth and appears to correspond to the steeply dipping subducting slab, penetrating through the 410 km discontinuity. Above 300 km, the slab anomaly exhibits large variations in its amplitude, and we are investigating whether this effect is real or due to uneven data distribution. A large low-velocity anomaly is observed in the uppermost mantle (~100 km) under the southern Altiplano near 21°S extending laterally to the east under the Eastern Cordillera. North and south of this anomaly the upper mantle appears to be more heterogeneous. We are adding to this data set by utilizing additional P-phases to improve the resolution of the images.
