HR: 0830h
AN: S41D-0110    [PDF]
TI: An investigation into crustal structure of South America; the continent that is missing some of its Moho
AU: * Sakaguchi, K
EM: ksa@email.arizona.edu
AF: University of Arizona, Department of Geosciences 1040 E.4th Street, Tucson, AZ 85721 United States
AU: Gilbert, H
EM: hgilbert@geo.arizona.edu
AF: University of Arizona, Department of Geosciences 1040 E.4th Street, Tucson, AZ 85721 United States
AU: Zandt, G
EM: zandt@geo.arizona.edu
AF: University of Arizona, Department of Geosciences 1040 E.4th Street, Tucson, AZ 85721 United States
AU: Beck, S
EM: beck@geo.arizona.edu
AF: University of Arizona, Department of Geosciences 1040 E.4th Street, Tucson, AZ 85721 United States
AB: Knowledge of the large-scale crustal structure of the South American continent is currently very sparse. In order to improve this situation we collected data from available permanent broadband seismometers in the GSN, GTSN, and Geoscope networks in South America to learn about crustal structure at each station. Data was obtained from 15 stations spanning South America from as far north as Venezuela to southern Argentina, and across the entire east-west extent of the continent. Five stations are located along the western coast of South America near the subduction zone in the forearc region west of the high cordillera of the Andes. Seven stations are located in the non-deformed shield part of the South American continent. Three stations are located in the actively deforming region of the Andes. The stations in the nearby Galapagos and Falkland Islands were also studied. We collected data from each of these stations for a time period between 1996 and 2002 and calculated nearly 1000 high quality receiver functions with the amount of data at each station ranging from less than ten to over 150. The receiver functions from these stations were investigated as a function of ray parameter and backazimuth to identify P-to-s conversions from the Moho and crustal multiples. The most striking observation we find is that we do not detect a clear Moho arrival at any of the five stations in the forearc region. This observation may be due to pervasive hydration of the forearc mantle resulting in the reduction of the shear velocity contrast at the base of the crust. We do however find a strong conversion that appears to occur at a depth corresponding to the top of the subducting slab in the range of 60-80km at these stations. The Moho under the stations in the cratonic crust can be clearly seen in the depth range of 34-47 km and Vp/Vs values are in the range of 1.63 to 1.88. We do not detect a clear geographic pattern in changes in crustal thickness and Vp/Vs across the continent, but we are currently comparing crustal properties and surface geology to find additional correlations.
DE: 7205 Continental crust (1242)
DE: 7218 Lithosphere and upper mantle
SC: Seismology [S]
MN: 2003 Fall Meeting