HR: 1340h
AN: S13B-1054    [Abstracts]
TI: An Investigation of Crust and Upper Mantle Structure in Western Argentina Utilizing Local Event Receiver Functions
AU: * Calkins, J A
EM: jcalkins@geo.arizona.edu
AF: University of Arizona, 1040 E. Fourth Street, Tucson, AZ 85719 United States
AU: Zandt, G
EM: zandt@geo.arizona.edu
AF: University of Arizona, 1040 E. Fourth Street, Tucson, AZ 85719 United States
AU: Gilbert, H
EM: hgilbert@geo.arizona.edu
AF: University of Arizona, 1040 E. Fourth Street, Tucson, AZ 85719 United States
AU: Beck, S
EM: beck@geo.arizona.edu
AF: University of Arizona, 1040 E. Fourth Street, Tucson, AZ 85719 United States
AB: Images of the crust-mantle boundary and crustal structure obtained using the traditional analysis of teleseismic receiver functions (RFs) exhibit an unusually weak P-S conversion from the Moho in Western Argentina, where the subducting Nazca plate temporarily flattens out beneath the overriding South American plate. In order to better estimate depth to the Moho and search for mid-crustal impedance contrasts, we calculate and stack receiver functions using approximately 45 local earthquakes occurring in the downgoing slab between December of 2000 and February of 2001. The events occurred over a depth range of 76 to 165 km and were all within 128 km horizontal distance of the recording station and thus traveled with ray parameters less than .09 s/km. Radial receiver functions are calculated at two temporary broadband seismic stations located between San Juan and Mendoza, in the region where the Precordillera transitions eastward to the Sierras Pampeanas. Plots of stacked RFs as a function of ray parameter show a strong signal from the Moho at 7 seconds corresponding to a depth near 50 km, as well as conversions from interfaces within the crust at depths of $\sim$ 20 and 35 km. It should be noted that the narrow time interval between the P and S arrivals, due to the close proximity of events to the stations, precludes the analysis of reverberations within the crust to better constrain crustal Vp/Vs estimates and to refine the depth to interfaces. The observed Moho depth is in good agreement with estimates made using Pn apparent phase velocities along a transect through tectonically similar terrain 200 km to the north. In both cases, areas of relatively low topography are underlain by anomalously thick crust. The discrepancy in the clarity of the Moho Ps between RFs obtained using teleseismic versus local events currently remains unexplained but is an area of ongoing research.
DE: 7294 Instruments and techniques
DE: 7205 Continental crust (1242)
DE: 1734 Seismology
DE: 0902 Computational methods, seismic
DE: 0935 Seismic methods (3025)
SC: Seismology [S]
MN: 2004 AGU Fall Meeting