HR: 17:48h
AN: T54A-09    [Abstracts]
TI: Identification of PKJKP using data from a Broad-band Seismic Array
AU: * Cao, A
EM: acao@seismo.berkeley.edu
AF: Berkeley Seismological Lab University of California, Berkeley, 215 McCone Hall, Berkeley, CA 94720 United States
AU: Romanowicz, B
EM: barbara@seismo.berkeley.edu
AF: Berkeley Seismological Lab University of California, Berkeley, 215 McCone Hall, Berkeley, CA 94720 United States
AU: Takeuchi, N
EM: takeuchi@seismo.berkeley.edu
AF: Berkeley Seismological Lab University of California, Berkeley, 215 McCone Hall, Berkeley, CA 94720 United States
AB: The solidity of the inner core, first proposed by Inge Lehmann in 1936, was confirmed using seismic normal mode observations more than three decades ago. Since then, significant progress has been made in documenting the sharpness of the Inner Core Boundary (ICB), and in the inner core, the existence of P-wave anisotropy, as well as various features of the P-wave velocity and attenuation and some constraints on the solid-state mineralogical texture. However, direct evidence for the solid inner core, PKJKP (traversing the inner core as a shear wave), is still a topic of debate. Very few studies have addressed this issue, and each of them has generated some level of skepticism about the reliability of the observations. Using stacked broadband records from the high quality Graeffenberg network in Germany, we here document the observation of a high signal to noise phase on the vertical component, whose arrival time and slowness are in agreement with predictions for PKJKP from the seismic reference model PREM. The high quality of the observed waveform provides us a unique opportunity to verify whether what we observed is a real PKJKP phase. For this we use two distinct approaches: (1) comparison with unambiguous synthetic PKJKP phases without any interference from mantle phases. The resulting vespagram is very compatible with the observed one. (2) waveform modeling. Taking both solid and liquid inner core into account, we discuss the possible interfering phases (including unidentifiable mantle multiples) in detail. Our results show that the most likely influence on our observed PKJKP is from a mantle multiple. However, its slowness is positive, whereas the slowness of our observed PKJKP is negative, and so it can clearly be distinguihsed from PKJKP. This observed PKJKP waveform also allows us to estimate $Q_\beta$ in the central part of the inner core. We find a somewhat higher value than that of PREM, indicating an increase of $Q_\beta$ with depth in the inner-core, in agreement with what is generally observed for $Q_\alpha$.
DE: 7207 Core and mantle
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting