HR: 10:35h
AN: S31H-02    [PDF]
TI: Probing the Southern Indian Shield with {\it P}-Wave Receiver-Functions
AU: * Tseng, T
EM: tseng1@uiuc.edu
AF: University of Illinois, Department of Geology, 1301 W. Green St., Urbana, IL 61801 United States
AU: Chen, W
EM: wpchen@uiuc.edu
AF: University of Illinois, Department of Geology, 1301 W. Green St., Urbana, IL 61801 United States
AU: Zou, Z
EM: zzou@uiuc.edu
AF: University of Illinois, Department of Geology, 1301 W. Green St., Urbana, IL 61801 United States
AB: We demonstrate a rare, successful case of using {\it P}-wavefield recorded on vertical-component seismograms alone to constrain crustal properties of the southern Indian shield. The data comprise of digital seismograms recorded by the short-period Gauribidanur Array (GBA) situated on Archean crust. The {\it P}-wavefield contains critical information, such as average speed of the {\it P}-wave in the crust ({\it V$_{P}$}), which is obscured in standard receiver-functions based on {\it P} to {\it SV} conversions. Moreover, conventional receiver-functions require all three components of seismograms, thus tripling the workload. In contrast to previous reports of {\it P}-wave receiver functions where the results have been equivocal, primary reflection off the Moho, the {\it PpPmp} phase, is visible and coherent in unprocessed data across the GBA array where the signal-to-noise ratio is excellent. We use eigen-image decomposition to estimate the source wavelet whose effect (including the instrument response) is then removed from seismic profiles by deconvolution. The resulting profiles show that the coda of {\it P}-wave is dominated by the {\it PpPmp} phase, whose uniform timing relative to the direct {\it P}-phase indicates a sharp, sub-horizontal Moho beneath GBA. Building upon previous reports of crustal thickness (35 $\pm$ 2 km) and average speed of the {\it S}-wave in the crust ({\it V$_{S}$}, 3.60 km/s), the {\it P}-wave receiver functions indicate a {\it V$_{P}$} of 6.4 $\pm$ 0.1 km/s in the crust. Low values of {\it V$_{P}$}, {\it V$_{S}$}, and the Poisson ratio (0.268 $\pm$ 0.011) are consistent with well-constrained results from Hyderabad, bolstering the interpretation that the entire thickness of Archean crust in southern India is felsic to intermediate in composition.
DE: 7200 SEISMOLOGY
DE: 7205 Continental crust (1242)
SC: Seismology [S]
MN: 2003 Fall Meeting