HR: 16:00h
AN: S34C-01    [Abstracts]
TI: Determination of Inner Core Rotation Rate: Preliminary Results From ARCTIC PASSCAL Experiment
AU: * Song, X
EM: xsong@uiuc.edu
AF: University of Illinois at Urbana-Champaign, Department of Geology, 1301 W. Green St. 245 NHB, Urbana, IL 61801 United States
AU: Christensen, D H
EM: doug@giseis.alaska.edu
AF: University of Alaska Fairbanks, Geophysical Institute, 903 Koyukuk Drive, Fairbanks, AK 99775 United States
AU: Dai, W
EM: weidai2@uiuc.edu
AF: University of Illinois at Urbana-Champaign, Department of Geology, 1301 W. Green St. 245 NHB, Urbana, IL 61801 United States
AB: Recent study by Zhang et al. (Science, 2005) provided strong support for inner core rotation. The doublet technique employed put a tight constraint on the temporal change of travel times through the inner core along the South Sandwich Islands (SSI) to Alaska pathway of about 0.0090 s/yr. Determination of the rotation rate, however, requires knowledge of underlying structure. We recently deployed 15 PASSCAL seismic stations in the interior of Alaska. The experiment, coded as Alaska Receiving Cross-Transects for the Inner Core (ARCTIC), consists of two linear arrays north of and west of Fairbanks, Alaska, respectively (http://www.geology.uiuc.edu/~xsong/arctic/arctic.html). The NS array is designed to provide critically needed samples for imaging the lateral variation of the inner core structure as illuminated by SSI earthquakes. The EW array is designed to provide critical samples at continuous distances for depth-dependence of the inner core anisotropy and attenuation. The new data collected will also be used to elucidate crustal and upper mantle structure of the Alaska interior. We installed three stations (for testing purposes) along the NS line in August, 2004, and the rest of the stations this summer. The stations will be deployed until the late summer of 2007. Over the last 13 months, we recorded 21 SSI earthquakes with m_b >= 5.2, among which 16 has m_b >= 5.4. This seismicity rate is about the same as the average rate over the last four decades. Combined with existing stations, our new stations provide samples of the inner core underneath the central America across a lateral range of 30 degrees in longitude. Preliminary analysis suggests a strong lateral velocity gradient in the inner core with the velocity decreasing from west to east. Our new samples are consistent with predictions for a super-rotation of the inner core.
DE: 7203 Body waves
DE: 7207 Core (1212, 1213, 8124)
DE: 7294 Seismic instruments and networks (0935, 3025)
DE: 8115 Core processes (1213, 1507)
SC: Seismology [S]
MN: Fall Meeting 2005