Earth Planets Space, Vol. 57 (No. 4), pp. 271 -280, 2005
D.S.Ramesh1, H.K wakatsu2, S.Watada2, and X.Yuan3
1National Geophysical Resear h Institute,P.B.724,Hyderabad-500007,India
2Earthquake Resear h Institute,University of Tokyo,1-1-1 Yayoi,Bunkyo-ku,Tokyo 113-0032,Japan
(Received November 1,2004;Revised March 16,2005;Accepted March 16,2005)
Crustal confguration of the central Chugoku region with disposition of the Philippine Sea Plate (PHS)in this area are investigated through the receiver function approach using short-period Hi-net data.Images of the upper mantle discontinuities are also obtained.Restituted short-period receiver functions bring out discernible variations in verage composition of the crust and its thickness in the study region.The Vp /Vs values in the study area are generally high,reaching values in excess of 1.85 at few places.The central part of the study region showing the highest Vp /Vs values is coincidentally subregion of least seismicity,possibly bestowed with special subsurface structure.Migrated receiver function images,both Ps and Pps images,unambiguously trace the NW subducting PHS taking steeper plunge in the northwest part of the Chugoku region reaching depths of 70 km from its low dip disposition in the southeast.An excellent correlation of the subducting PHS with the hypocenters is also seen.We demonstrate that short-period data after restitution and application of appropriate low pass flters can indeed detect presence of the global 410-km and 660-km discontinuities and map their disposition reasonably well.Our migrated receiver functions image the deflections in the 410-km and 660-km discontinuities in n anti-correlated fashion on expected lines of Clapeyron slope predictions induced by subduction of the Pacific plate (PAC)beneath Japanese islands,though PAC itself is feebly traced but shows good correlation with slab seismicity.
Key words: Central Chugoku,Hi-Net,Japan,Migration,Receiver Functions,Short period data.