HR: 0800h
AN: DI31A-0250    [Abstracts]
TI: Seismic Evidence for a Distinctly Anisotropic Innermost Inner Core
AU: Chen, Q
EM: chenqf@seis.ac.cn
AF: Institute of Earthquake, Science China Earthquake Administration, No.63 Fuxing Avenue, Beijing, 100036, China
AU: * Niu, F
EM: niu@rice.edu
AF: Department of Earth Science, Rice University, 6100 Main Street, Houston, TX 77005, United States
AB: We observed clear underside reflections at the inner core boundary, PKIIKP, at two broadband seismic arrays in Venezuela and China from two deep focus earthquakes occurring in Indonesia and Argentina. Since PKIIKP traverses a very similar ray path with PKIKP, we anticipate that the differential travel time between PKIIKP and PKIKP is mostly sensitive to the seismic structure of the inner core. The uppermost 400 km of the inner core is also expected to produce no significant anomalies to the differential travel time along these two paths based on current inner-core models. The differential travel time is thus mainly subjected to heterogeneities and/or anisotropy in the center of the earth that affect the travel time of PKIKP. We found that the Indonesia-Venezuela path exhibits a ~1.8 s positive differential travel-time residual while the Argentina-China path shows no significant anomaly with respect to PREM. As the Indonesia-Venezuela and Argentina-China paths are in the directions of ~8° and 28° from the equatorial plane, respectively, our observation suggests that the slowest direction of wave propagation is no longer in the east-west direction for the innermost inner core. The Earth's center has a distinct seismic anisotropy relative to the rest part of the inner core.
DE: 7203 Body waves
DE: 7207 Core (1212, 1213, 8124)
SC: Study of the Earth's Deep Interior [DI]
MN: 2007 Fall Meeting