HR: 0830h
AN: T11C-0398    [PDF]
TI: Seismic structure near the inner core boundary around the South Pole
AU: * Ohtaki, T
EM: t-ohtaki@aist.go.jp
AF: Geological Survey of Japan, AIST, AIST Tsukuba Central 7, Tsukuba, 305-8567 Japan
AU: Kaneshima, S
EM: kane@geo.titech.ac.jp
AF: Dept. Earth and Planetary Science, Tokyo Institute of Technology, Ookayama, Tokyo, 152-0033 Japan
AU: Kanjo, K
EM: kkanjo@met.kishou.go.jp
AF: Matsusiro Seismological Observatory, JMA, Matsusiro, Nagano, 381-1232 Japan
AU: Inoue, H
EM: inoue@bosai.go.jp
AF: National Research Institute for Earth Science and Disaster Prevention, Tennoudai, Tsukuba, 305-0006 Japan
AU: Purwana, I
EM: ibnu@bmg.go.id
AF: Bureau of Meteorology and Geophysics, Jl Angkasa I No.2 Kemayoran, Jakarta, 10720 Indonesia
AB: We deployed the broadband seismic network in central and western Indonesia called JISNET. Seismic waves from earthquakes of the southern South America to Indonesia pass through in the inner core beneath Antarctica. Using the waveforms observed at JISNET and other broadband stations around Indonesia, we analyze the seismic structure near the inner-core boundary (ICB) around the South Pole. We chose the data whose turning point of PKPdf or one of its intersections at the ICB is located at south of 70$\deg$S, and of good S/N ratio. We selected 89 vertical component seismograms for the 15 earthquakes from 1998 to 2002 whose core phases that meet the above-mentioned criteria are observed in more than 4 JISNET stations. The epicentral distances of the data we selected are from 130 to 164 degrees. We computed the synthetics using the Direct Solution Method (Takeuchi et al., 1996) with the earth reference model PREM. The observed and synthesized waveforms are bandpass-filtered at frequencies between 0.01-0.5 Hz. Our preliminary waveform analysis shows that the observed waveforms require a 150-km thick constant velocity zone above the ICB and the low velocity below the ICB. There remains trade-off between the low velocity zone in the outer core and low Q in the inner core. We evaluate the effect of the low Qp model which has Qp=200 in the uppermost 100 or 200 km of the inner core on the synthesized waveforms, and found that it does not significantly affect the result. This low velocity zone above the ICB is consistent with the results of previous travel-time studies (e.g., Souriau and Poupinet, 1991). We will also show whether the waveforms from earthquakes of north South America to JISNET, which pass through beneath the equatorial area, will require the same seismic structure near the ICB as that beneath the South
DE: 1213 Earth's interior--dynamics (8115, 8120)
DE: 7207 Core and mantle
DE: 8115 Core processes (1507)
SC: Tectonophysics [T]
MN: 2003 Fall Meeting