上地壳二维 Pg波成像方法及几个应用实例

裴顺平

中国科学院青藏高原研究所

2012-11-08, 中科大

Moho

3D Tomography

(张国民等， 2002)

2D Pg Tomography

2 2( ) / /obs sta evtt h v v t t

ij i j ijk kk

t a b d s

obs sta evtt t t t 2 2 /t h v

(Pei and Chen, 2012, BSSA)

Anisotropy

ij i j ijk kk

t a b d s ( cos 2 sin 2 )ij i j ijk k k k

k

t a b d s A B

波速各向异性的大小为

波速最快方向方位角为 1/2arctan(Bk/Ak) +90

2/122 )( kk BA

(Pei et al., 2012, Tectonophysics)

ij i j ijk kk

t a b d s Ax b

Earthquake

Station

M oho kijkjiij Sdbat

2sin2cos kkkk BAsS

Pn Tomography

(Pei et al., 2007, JGR)

ML Amplitude Tomography

Source

Station

Crust

Upper mantle

( ) ( ) ( ) ( ) ( ) ( , )ij j i i ij ijA f O f I f S f G R B f R1

0ln ( ) ln ( )ij ij ij i jY A f G R a b Q cR

(Pei et al., 2006, BSSA)

2D Pg Tomography

2 2( ) / /obs sta evtt h v v t t

ij i j ijk kk

t a b d s

obs sta evtt t t t 2 2 /t h v

(Pei and Chen, 2012, BSSA)

实例一：玉树地震

(Pei and Chen, 2012, BSSA)

Weimin Wang et al.

Yong Zhang et al.

Koketsu et al.

7157 Pg arrival times1689 Earthquakes 11 Stations

Depth ：8.6 2.1 km

Epicenter Distance:76 38 km

0.046.02

t

Resolution Test15’ 15’

Table 1. Average velocity in the three sub-regions

Sub-region Number of ray paths Average velocity (km/s) Tomographic velocity A 672 6.45 Fast anomaly B 363 5.82 Slow anomaly

C 163 5.83 Slow anomaly

稳定性测试

• Origin time 0.2s errors

• Source depth 10km

• Both

Why Anisotropy

• Anisotropy ？• Crack direction

• Crack density

(Pei et al., 2012, Tectonophysics)

120

(Pei et al., 2012, Tectonophysics)

Without Anisotropy With Anisotropy

（ Yao et al ， 2010）

Summary

• Simple 2D tomography method

• Seismic velocity structure controls the origination (stress accumulation) and rupture propagation and distribution of aftershocks as well

• Pg anisotropy implies direction and density of micro-crack

总结

• Pg 二维成像方法简单有效• 高分辨率成像能够提供新的结

构信息（裂隙，介质变化）• 浅层精细结构能够提供地质可

比性