A ne w method f or seismic imaging from ambient seismic noise

Transcription

1 2 2 3 Vol. 22 No ( :771777) PRO GRESS IN GEOP H YSICS J une , 2, 2 (1., ; 2., ),,,,.,,.,,..,,, P315 A (2007) A ne w method f or seismic imaging from ambient seismic noise Q I Cheng 1, CH EN Qi2f u 2, CH EN Yong 2 (1. Institute of Geology and Geophysics, Chinese A cademy of Sciences, Beijing , China; 2. Institute of Earthquake science, China Earthquake A dministration, Beijing , China) Abstract Recently, one of the hotly discussed problems in multidisciplinary fields is to use ambient seismic noise to extract the Green s function, i. e., cross2correlating the seismic noise recorded by two stations to get the Green s function between these two stations, thus to improve our knowledge about subsurface structures by use of seismic im2 aging. In this paper, the developing background and process of this new method will be introduced firstly. And then it s physical p rinciple will be also shown f rom four different viewpoint s. If this method could be developed more, seis2 mic images with high resolution will be acquired without natural earthquakes or artificial explosions, but just the seis2 mic ambient noise. This new method may greatly advance the development of seismology. Keywords ambient seismic noise, Green s f unction, cross2correlation, seismic imaging 0, ().,, [13 ].,,, [ 4 ].,,,.,,,.,. [5 ] [610 ], [1113 ] [1419 ]..,,,., ; ( ).,,1979,2001,.. ( E2mail ac. cn)

2 , :,,,. :. 1987,Steve Cole, [20 ]. Stanford 1,4,096. (plunging waves),,.,, 10 Hz.,Cole,, [ 5 ],. [ 21 ]. acoustic daylight imaging, Michelson Doppeler Imager ( MDI),. ( )., -,.,., [5 ]?, Weaver [6,7 ],(t hermal fluct uation),,,.,campillo [14 ].,, (coda). 101, one2 bit [22 ],.,,Rayleigh Love. Weaver [6 ], ( modal equiparti2 tion).,.,,,,. Hennino,, [23 ]. Shapiro 2005 [18 ]. U SArray 62,,(718 s).,7. 5 s 15 s, km..,,.,, [24 ] [25,26 ]., [27 ]. Roux [ 19 ],,. Rayleigh..,,,. [28 ], [ 29 ] [30 ], [31 ] [32 ]., [33 ]., [34 ].,,. Roux [19 ] 11,

3 3,: 773, Rayleigh,- P. P? Roux P. P, Rayleigh,, Rayleigh. P Rayleigh, P.,,.. (passive imaging).,,. 2,? Joint Assembly,.,., A GU, Hearing the Noise,,Joint Assembly. 1.,,,.,, [35 ] Weaver, [7 ].,. [7,16 ]. ( x, t) = a n u n ( x) e i n t, (1) n x, t, un n, an. : g ana 3 m g = nm F ( n ), (2) kronecker, F ( ).,, x y : C( x, y, ) = F ( n ) un ( x) un ( y) e - i n. (3) n

4 [36 ]. 2. 2,,. Derode (time2re2 versal symmetry) [ 37,38 ]., A B C. C, e( t), A B A ( ) = e( t) g h AC ( t) B ( ) = e( t) g h BC ( t), g. A B : C AB ( t) = < A ( ) < B ( t + ) d = h AC ( t) g h BC ( - t) g e( t) g e( - t), (4) :B,C h CB ( t),,, A h CB ( - t) g h AC ( t).,, h CB ( - t) g h AC ( t) = h AC ( t) g h BC ( - t). C,A B h AC ( t) g h BC ( - t).,a B h AB.,C,. Helmholtz2Kirchhoff, C,., B,, C.,.,,A h BA ( - t)., B ( t = 0), B,t > 0 A h BA ( t)., C, : C h AC ( - t) g h CB ( t) = h BA ( t) + h BA ( - t), (5),,,C,. [39 ] Snieder [ 17 ] Campillo Paul [14 ],. (stationary p hase approximation), [ 17,40 ]., x (0,0,0) ( R,0,0), c...,, : C( ) = 8 2 S ( ) 2 c i e 4R i kr 0 - nd x - e 4R - ikr R nd x, (6) n, S ( ) 2 s S s ( t). - exp ( i k R) / 4R, x < 0, x, (retarded). - exp ( - ik R) / 4R, x > R, x, (advanced).,,, Claerbout [41 ], Wapenaar [ 15 ],,.,.,,., : 5 D 0 { ( P+ A ) 3 P + B - ( P ) 3 P - Ā B } d2 x = 5 D m { ( P+ A ) 3 P + B - ( P ) 3 P - Ā B } d2 x, (7) P, A B, 5 D0 5D m. P + P -. 3., 5 D0 5 D m,

5 3,: 775., 5D0.,, R + 0 ( x A, x B, ) = R + 0 ( x B, x A, ), (8), : 2 R[ R + (x A,x B,) ] = (x H,B - x H,A ) - 5D m { T- (x A,x, ) } 3 T - (x B,x, ) d 2 x, (9) R[ g ]., R + ( x A, x B, ) T - ( x A, x, ) T - ( x B, x, ), { T - ( x A, x, ) } 3 T - ( x B, x, ) ( x A x B ).,,., 3 [ 46 ].,.,,,.,,...,.,?.,?.?,,, 4D?..,,, ;,,,,..,,.,,,.,...,.,., [16 ].,,. [ 42,43 ],.,Apollo 17,, 10 m [44 ]., ( ),,,. ( Urban Geo2 p hysics), [45 ].,,.,. ( References) : [ 1 ],,,. [J ].,2003,18 ( 4) : [ 2 ],,,,. [J ].,2006,21 (3) : [ 3 ],,,.. [J ].,2005,40 (2) :

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