日本列岛下太平洋俯冲板块的精细结构

第15卷第1期2008年1月

地学前缘(中国地质大学(北京);北京大学)

Earth Science Frontiers (Chin a University of Geosciences,Beijing;Peking University)Vol.15No.1Jan.2008

收稿日期:2007-06-29;修回日期:2007-09-19

基金项目:日本文部科学省科学研究项目(Kiban -A 17204037)

作者简介:江国明(1979 ),男,博士研究生,地球探测与信息技术专业,主要研究方向为天然地震的层析成像。E -m ail:jiang gu om ing@

;jiang@aob.geoph ys.tohoku.ac.jp

日本列岛下太平洋俯冲板块的精细结构

江国明

1,2

, 赵大鹏2, 张贵宾

1

1 中国地质大学(北京)地球物理与信息技术学院,北京100083

2 日本东北大学地震预测与火山研究中心,日本仙台980-8578

Jiang Guo ming 1,2

, Zhao Dapeng 2

, Zhang Guibin

1

1 S ch ool of G eop hy sic s and I nf or mation T echnolog y ,Ch ina Unive rsity of Ge oscience s(B eij ing ),Beij ing 100083,China

2 De par tme nt of Ge op hy sics ,T ohoku Univ ersity ,S end ai 980-8578,J ap an

Jiang Guoming,Zhao Dapeng,Zhang Guibin.Detailed structure of the subducting Pacific slab beneath the Japan islands and Ja -pan sea.Earth Science Frontiers ,2008,15(1):222-231

Abstract:A lt ho ug h many studies have been made to image the subduct ing Pacif ic slab in and aro und t he Japan islands,deta ils of t he slab st ruct ur e (such as the slab thickness,its seismic v elocit y,the subducting o ceanic crust,as well as the depth var iatio ns o f these factor s)are still unclear.In this study,we have addressed this issue by using ar riv al times o f int er mediate -depth and deep ear thquakes r eco rded by the dense seismic netwo rk on t he Ja pan islands.W e adopted a fo rw ard -modeling approach with a 3-D ray -tracing technique.We fir st used 333teleseismic ev ents and fo und that the thickness o f the Pacif ic slab beneath Japan is 85km.We t hen used 130227P -w ave trav el times fr om 3283local and regional ear thquakes w ith fo cal depths g reater than 40km to study the detailed structur e o f the subducting Pacific slab.Our results sho w that the av erag e velocit y per tur ba -tions of the slab in 6depth r ang es ar e 5 5%,4 0%,3 5%,2 5%,2 0%and 6 0%,r espectiv ely T he per -tur bat ions in the dept h r ang e of 40-500km decr ease wit h depth,w hich is consistent w ith the patter n of in -cr easing temperature with depth Ho wev er,at depths gr eater than 500km,the per tur bat ion amo unts to 6 0%,which may be caused by the larg e uncerta int y in the hy pocenter locations o f the v ery deep ear thquakes under the East Asia continent mar gin F inally,w e used the local and reg ional events wit h focal depths from 40to 500km to study the subducting o ceanic crust beneath No rtheast Japan and H okka ido Our r esult s sho w that the o ceanic crust ex tended do wn to 110km depth under both r egions,t he averag e thickness of the oceanic crust is 7 5and 5km,and the velocity per tur bat ion in the oceanic cr ust relative to the 1-D model is 1%and -3%,respectively T hese r esults can be int erpreted that the oceanic cr ust has dehy dr ated and metamor phosed g radu -ally because of the increasing temperature and pr essure wit h depth A fter analyzing the relatio nship betw een the hypocenters and the o ceanic crust,we co nsider that t he lar ge difference (1%and -3%)is pro bably caused by mor e fluids (such as wat er)in the o ceanic crust beneath H okka ido t han that beneath N or theast Japan T he state of the oceanic cr ust beneat h southern Japan w as not determ ined because mo st o f the r egion is co ver ed by the ocean and so ther e are few stat ions there

Key words:the subducting P acific slab;detailed structure;3-D r ay tr acing ;fo rw ard -modeling ;o ceanic crust