HR: 0800h
AN: U41B-0411    [Abstracts]
TI: More Seismic Evidence for a Sharp Edge to the Large Low Shear Velocity Anomaly Beneath the Pacific Anomaly
AU: * Zhao, C
EM: zhaochp@asu.edu
AF: Arizona State University School of Earth and Space Exploration, Arizona State University, PO Box 871404, Tempe, az 85287-1404, United States
AU: Garnero, E
EM: garnero@asu.edu
AF: Arizona State University School of Earth and Space Exploration, Arizona State University, PO Box 871404, Tempe, az 85287-1404, United States
AB: A number of seismic investigations have well documented a sharp transition between the large low shear velocity province (LLSVP) beneath the Pacific and Africa and the surrounding lower mantle. Using USArray recordings of Fiji-Tonga and Kemadec events, we study the northern portion of the LLSVP beneath the Pacific. For this geometry, normal and multi-pathed SH phases are apparent, along with rapidly changing arrival times consistent with a sharp boundary there. Wave paths sample the implied edge somewhat obliquely, resulting in strong waveform broadening in data that sample within a few hundred kilometers of the transition. A rapid change in SH- wave travel times of up to 8 s relative to the PREM reference model are observed, compared with little change relative to PREM for P wave arrival times. Such acute variations in waveforms and travel times for signals with comparable wavelengths are quite consistent with SH multipathing. Our analyses suggest a sharp lateral transition from a broad slow region to a relatively fast region in the lowermost mantle. We observe a different scaling between P and S velocities within and outside of the LLSVP, implying chemical differences between the LLSVP and the surrounding lower mantle, as well as providing a constraint on deep mantle mineralogy.
DE: 7200 SEISMOLOGY
DE: 7203 Body waves
DE: 7207 Core (1212, 1213, 8124)
DE: 7208 Mantle (1212, 1213, 8124)
SC: Union [U]
MN: 2007 Fall Meeting