Along-strike variations of crustal reflectivity related to the Andean subduction process

Abstract

This paper presents the results of Kirchhoff prestack depth migration applied to two onshore deep seismic reflection data sets (ANCORP'96 and PRECORP'95). The prestack depth migration method was implemented in 3D (ANCORP) and in 2D (PRECORP), respectively, from topography. Selective stacking of the migrated depth slices yielded a 3D depth volume (ANCORP) and a 2D depth section (PRECORP), respectively. An additional "offline stacking" provided a final 370 km long 2D depth section (ANCORP). In this paper a 180 km long depth section will be presented. At the beginning of the ANCORP section a double reflection zone is observed, which is associated with the upper and lower boundary of the oceanic crust. Except for some areas a nearly complete image of the Nazca reflector at depths between 60-90 km has been obtained. Moreover, one Bright Spot in each section has been detected: the Quebrada Blanca Bright Spot (QBBS, ANCORP) and the Calama Bright Spot (CBS, PRECORP). The reprocessing yielded two new aspects regarding these structures: Besides the west dip of the QBBS, which was already known from standard poststack processing results, a 3D analysis of the ANCORP data set shows an additional north-dipping trend of the QBBS. Furthermore, the CBS is discovered for the first time.