HR: 1400h
AN: S33A-04    [Abstracts]
TI: Discriminating Hidden Structures Beneath the Paraná Basin With Receiver Functions
AU: Julià, J
EM: jordi@seis.sc.edu
AF: Department of Geological Sciences University of South Carolina, 701 Sumter St., Columbia, SC 29208, United States
AU: * Assumpção, M
EM: marcelo@iag.usp.br
AF: Departamento de Geofísica - IAG Universidade de São Paulo, Rua do Matão, 1226 Cidade Universitária, São Paulo, SP 05508-090, Brazil
AB: We investigate the seismic structure of the crust and uppermost mantle beneath the intracratonic Paraná basin of SE Brazil by analyizing P- and PP-wave receiver functions at 14 broadband stations within the basin. The stations were deployed by the University of São Paulo during the 1992-1995 and 2002-2005 Brazilian Lithosphere Seismic Project experiments and cross the surface projection of several independently proposed locations for a suspected cratonic nucleous presently hidden under the basin's sediments. Discriminating among competing hidden structures is critical for our understanding of the subsidence and formation mechanisms of the basin. Analysis of the phase moveout of the Moho interaction phases observed in the computed receiver functions reveals crustal thickness and bulk Vp/Vs ratio variations in the 40-48 km and 1.71- 1.76 ranges, respectively. Joint modeling of receiver function waveforms with independent local surface-wave dispersion velocities yields S-wave velocity variations with depth beneath each station that suggest the highest Vp/Vs ratios are the result of mafic underplating roughly along the basin axis. The overall pattern displayed by our measurements is thus consistent with a hidden structure consisting of several cratonic blocks separated by underplated rift segments, which suggests the locus of subsidence was defined by a preexisting zone of weakness and driven by the gravitational pull of underplated mafic material.
DE: 7203 Body waves
DE: 7205 Continental crust (1219)
DE: 8038 Regional crustal structure
DE: 8103 Continental cratons
DE: 8169 Sedimentary basin processes
SC: Seismology [S]
MN: 2007 Joint Assembly