HR: 0800h
AN: DI41A-1250    [Abstracts]
TI: North Pacific Transition Zone Thickness From SS-Precursors
AU: * Mayeau, T M
EM: tmayeau@nmt.edu
AF: Department of Earth and Environmental Science, New Mexico Tech, Socorro, NM 87801 United States
AU: Wysession, M E
EM: michael@seismo.wustl.edu
AF: Department of Earth and Planetary Science, Washington University, St. Louis, MO 63130 United States
AU: Aleqabi, G I
DI41A-1250 AF: Department of Earth and Planetary Science, Washington University, St. Louis, MO 63130 United States
AB: The thickness variation of the mantle transition zone is one key to understanding mantle dynamics, in particular, as a possible indicator of lateral temperature variations at that depth. As a result of the Clapeyron slopes of the 410 and 660 km phase transitions, the transition zone is expected to thin in regions of high heat and thicken in cooler areas. Thus, these variations can be used to look for large scale mantle convection features, such as down going slabs and mantle plumes. The thickness of the transition zone can be effectively measured by the differential travel times of phases reflecting off the 410 km and 660 km discontinuities. Here we search for transition zone thickness variations using SS-precursors from the North Pacific recorded by the IRIS PASSCAL Florida-to-Edmonton (FLED) Array of broadband seismometers (and neighboring North American stations), which were operational from May 2001 to September 2002. Records are first rotated into transverse components, converted to displacements with the instrument responses removed, and then subdivided into 20 degree by 20 degree bins. The traces from earthquakes with strong SS arrivals were binned by the location of the SS bounce point, and the bins stacked into vespagrams using the MATLAB-based MATSEIS program. From the vespagrams we determine the S660S-S410S differential travel times for each stack, which yield measurements of transition zone thickness. We then compare thickness measurements from different events and with previously published maps of transition zone thickness to determine the robustness of our technique. This work was supported by an IRIS Undergraduate Summer Internship.
DE: 7208 Mantle (1212, 1213, 8124)
DE: 8120 Dynamics of lithosphere and mantle: general (1213)
SC: Study of Earth's Deep Interior [DI]
MN: Fall Meeting 2005