HR: 1340h
AN: T43A-1313    [Abstracts]
TI: Characteristics of PKP-Cdiff coda observed with small-aperture seismic arrays
AU: * Tanaka, S
EM: tanaka@aob.geophys.tohoku.ac.jp
AF: Tohoku Univ. Grad. School Sci., Aramaki Aza Aoba 6-6, Aoba-ku, Sendai, 980-8578 Japan
AB: PKP-Cdiff is a compressional wave diffracted around the inner core boundary (ICB), which may contain much information on the structure of the ICB. Here I have determined slowness of PKP-Cdiff and its coda with small-aperture arrays as large as several kilometers in size to approach the unsettled issues on the origin of the PKP-Cdiff coda (Morita, 1987; Umetsu, 1989; Nakanishi, 1990). The short-period seismic array data is collected from the Prototype International Data Center (pIDC) of the International Monitoring System (IMS) as Koper et al. (2004) did. The criteria of data selection (focal depths greater than 100 km, mb greater than 5.5, epicentral distances from 153 to 160 degrees, the period since Jan. 1995 through Feb. 2000) yielded twenty-nine event-array pairs, the band-pass filters comprising sixteen frequency bands from 0.25 to 4 Hz with 0.5 Hz bandwidths were operated to the array seismograms. Then the beam-forming as functions of slowness and incident azimuth were applied to each band-pass filtered array record. The difference of array response functions were adjusted by using the phase weighted stack with variation of the power index of the phase stack. The stacked powers for the PKP-Cdiff coda were investigated on the vespagram for all the frequency bands and the slownesses were distributed around two peaks of 1-3 s/deg and 4-5 s/deg, corresponding to the slowness of PKP-Cdiff and PKP-AB, respectively. The incident azimuths concentrated around the great-circle directions connecting the events and arrays. The specific stacked powers with slowness of 1-3 s/deg observed at distance 153-155 degrees tended to occur just after the PKP-Cdiff first arrivals whereas those at 156-160 degrees scattered uniformly in the time window between PKP-Cdiff and PKP-AB and are a few around the PKP-Cdiff first arrivals. Such characteristics of the slowness filtered PKP-Cdiff coda imply that the PKP-Cdiff coda is affected with the ICB structure. Because the small first arrival and large coda observed around larger distances are similar to the characteristics of PKiKP coda observed in 50-90 degrees by Vidale and Earle (2000) and Koper et al (2004), the nature of the PKP-Cdiff and its coda may reflect the scattering property of the ICB.
DE: 8115 Core processes (1507)
DE: 7203 Body wave propagation
DE: 7207 Core and mantle
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting