Observed patterns of high-frequency seismic wave attenuation suggest that near 22°S, the upper mantle structure beneath the central Andean plateau changes along strike to the south. The observations combined with data from previously reported wave propagation studies suggest that south of about 22°S, the upper mantle beneath the plateau and its adjacent foreland thrust belt is more highly attenuating than the upper mantle farther north. Foreward modeling of the Q measurements made at Jujuy indicates that the observations can be explained either by a variable thickness high-Q upper plate beneath the plateau, or by a thin, variable width, very low-Q zone in the asthenospheric wedge above the subducted slab. This lateral variation in upper mantle structure coincides with two physiographically distinct segments of the central Andean plateau and its adjacent foreland thrust belt to the east: the Bolivian Altiplano and Subandean ranges in the north and the Argentine Puna and Santa Barbara system in the south. -from Authors
