New Insights Into the Sierras Pampeanas Crust Using High Frequency Local Event Receiver Functions

Flat slab subduction of the Nazca plate beneath the western margin of South America is thought to control the tectonic deformation of the Andean Precordillera and Sierras Pampeanas between 30° and 32° S. Several arrays of broadband seismic instruments have been deployed in Chile and Western Argentina to study this phenomenon (e.g., CHARGE, 2000-2002; CHARSME, 11/2002-01/2003). In order to better constrain the crustal structure in the transition region between flat slab and normal subduction to the south, we have calculated local receiver functions from earthquakes occurring beneath the stations of the CHARGE and CHARSME arrays, and then compared results to published teleseismic receiver functions. Initially, 37 intermediate-depth local earthquakes recorded by the CHARGE array were used to calculate high frequency receiver functions at station JUAN. The improved vertical resolution afforded by the higher frequency content of the local earthquakes reveals complex layering throughout the crust below JUAN. Further, forward modeling of the combined local/teleseismic data set indicates a gradational increase in velocity in the lower crust. This initial study has since been expanded to the surrounding region using data from the more densely spaced three month CHARSME array, which was deployed directly above a cluster of earthquakes occurring near 100 km depth. The new results allow us to image differences between the adjacent Andean Precordillera and Western Sierras Pampeanas tectonic regimes. We present stacked receiver functions from the CHARSME array along with an analysis of the sensitivity of high frequency receiver functions to various filtering parameters and deconvolution techniques, using both real and synthetic data.