HR: 1330h
AN: T32B-0923    [PDF]
TI: Receiver Function Imaging of the upper mantle seismic discontinuities beneath the Japan Islands and the Korean Peninsula -Lateral variation in the depths and the Ps amplitudes-
AU: * Tonegawa, T
EM: tonegawa@eps.nagoya-u.ac.jp
AF: Nagoya University, Furoutyou, Chikusa-ku, Nagoya, 464-8602 Japan
AU: Hirahara, K
EM: hirahara@eps.nagoya-u.ac.jp
AF: Nagoya University, Furoutyou, Chikusa-ku, Nagoya, 464-8602 Japan
AU: Shibutani, T
EM: shibutan@eps.nagoya-u.ac.jp
AF: Kyoto University, Gokasho, Uji, Kyoto, 611-0011 Japan
AB: \hspace{1em}In the Japan Islands, high density short-period and broadband seismic networks have recently been installed. In this study, we apply Receiver Function (RF) analyses to teleseismic P-wave coda portions observed at 63 J-array, 64 F-net, 4 IRIS and 7 KIGAM (Korea) broadband stations and investigate the detailed structure of the upper mantle velocity discontinuities beneath the Japan Islands and the Korean Peninsula. The results indicate that there are large lateral variations in visibility of the 410 km discontinuities, and the 410, 660 km discontinuities are affected by the subducting Pacific (PAC) slab. \par \hspace{1em}We examine the observed waveforms from the teleseismic events with the magnitudes greater than 5.5, which occurred during a period from 1998 to 2003. We discard almost 35,000 RFs with low signal-to-noise ratios, and finally keep a total of 8,825 RFs from 389 events.\par \hspace{1em}RFs are constructed through frequency domain division of radial components by vertical ones with a water level of 0.01. The low-pass Gaussian filters of 0.1, 0.3, 1.0 Hz are also applied to examine the frequency dependence of the visibility of the discontinuities. Assuming the phases in RFs are produced by Ps converted ones at depths, we transform the time domain RFs to the depth domain ones using recent P- and S-wave tomographic velocity models. Then, SVD filtering is applied to the depth domain RFs. We keep largest 6 eigenimages to construct SVD-filtered RFs. Finally, we construct 2-D stacked RF images projected on cross-sections along several profiles to see the detailed velocity discontinuity structure.\par \hspace{1em}Beneath the Japan Islands, the dipping positive RF amplitude traces can be recognized to a depth of 200 km or more, which coincides with the distribution of deep earthquakes occurring within PAC. In contrast, the Philippine Sea slab has not been confirmed clearly. 660 km discontinuity is confirmed clearly and uniformly beneath the whole Japan Islands. Similarly, 410 km discontinuity is detected clearly in Kanto area (central Japan). However, in Tohoku (northern Japan) and southwest Japan area, 410 km one is not detected clearly. We consider that the reasons are both the density differences of the stations and the regional differences of the thickness of the 410 km discontinuity. Also, the 410 and 660 km discontinuities are undulated due to the subducting cold PAC slab. That is, in our results, the 410 km discontinuity seems to be locally affected where the PAC penetrates, and the 660 km discontinuity is broadly and gradually downwarped westwards by 50 km, which is consistent with the stagnated PAC on the 660 km discontinuity.\par \hspace{1em}We are grateful to the J-array, F-net, IRIS, KIGAM project for providing the data, and we are especially thankful to Prof. D. Zhao in Ehime University and Prof. K. Koketsu in Univ. of Tokyo for giving us 3-D P- and S-wave velocity models, respectively.
DE: 7218 Lithosphere and upper mantle
DE: 8124 Earth's interior--composition and state (old 8105)
SC: Tectonophysics [T]
MN: 2003 Fall Meeting