Mapping the Crustal Thickness of the Andes Using pmP Phases Identified From Adaptive Teleseismic Array Data

Crustal thickness (or Moho depth) is a key parameter for many geological and geophysical models. Despite this we have a limited number of measurements, typically from seismic receiver functions, to constrain variations in crustal thickness. Here we present an automatic methodology where we leverage array processing techniques and the increasing density of teleseismic data, to identify near-source Moho reflector phases, specifically pmP, from intermediate-depth and deep focus earthquake recordings. Using the differential travel times between the depth phase pP and its Moho precursor pmP to determine Moho depths at the pmP bounce points, we construct a crustal thickness map for the South American Subduction Zone, based on 2,588 pmP detections. The approach compares favorably to previous receiver function studies in the region, and enables the generation of continental-scale high resolution Moho depth maps with a greater number of defining data points, automatically, for supra-subduction zone regions, without the need for local instrumentation. Furthermore, we spatially analyze the relative amplitudes between pmP and pP, and infer dry, high velocity, uncoupled mantle overlying the Peruvian flat slab, which viscously couples at the distal bend subducting into the mantle. Overall, we present a powerful approach to study local to continental-scale crustal structure and subduction dynamics in areas with limited seismic infrastructure.