第十四讲地震波层析成像

Present Generation of models: Dense receiver sets, all rotating, ຫໍສະໝຸດ Baidureat coverage and crossing rays.
Brain Scanning Cool Fact:
According to an earlier report, the best valentine’s gift to your love ones is a freshly taken brainogram. The spots of red shows your love, not your words!
第六章 地震层析成像
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From IRIS
Seismic waves
• Seismic wave is currently the only effective tool that can penetrate the entire earth
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1939:
Jeffreys & Bullen
First travel-time tables：JeffreysBullen Seismological Tables
at 0 with an integral area of 1) p is also called sinogram, and it is a sine wave when f(x, y) is a point value.
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Shepp-Logan Phantom (human cerebral)
3. AK135 速度模型 Kennett et al. (1995)；
Montagner and Kennett (1996).
另外 还有： MC35， STW105， TNA/SNA.模型等
• • 莫霍诺维齐（前南斯拉夫）——莫霍面（壳幔边界） • －－地壳与地幔分界面的发现者
• 古登堡（美国）——核幔边界 • －－地幔与地核分界面的发现者
Cunningham & Jurdy, 2000
Broader fan beam, Moving source, fixed receivers, fast moving (1976)
Different “generations” of X-Ray Computed Tomography (angled beams are used to increase resolution). Moral: .good coverage & cross-crossing
• 莱曼（丹麦，女）—— （内外核边界）
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－－外核与内核分界面的发现者
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地球一维结构是远远不够的！ Plate tectonics
Topography
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mantle convection
Travel time table from ak135 model
Travel time picks
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Shearer, 2009
Input
Radon Projected
Recovered (output)
Back projection of the function is a way to solve f() from p()
(“Inversion”):
f ( x , y ) p ( x c y s o ) ) d i , s n
3-D variations of Earth’s Structure from Seismic Tomography
Seismic waves in the Earth
Traveltime/waveform
3-D wave speeds
Inverse problem
Researchers at MIT and Harvard, led by Keiti Aki and Adam Dziewonski in late 1970’s and 1980’s, pioneered the technique of se.ismic tomography.
→ 1D Earth model
Jeffreys-Bullen 1-D Earth Model
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地球内部结构
PREM一维全球速度模型
1. PREM参考地球模型： Preliminary Reference Earth Model (Dziewonski & Anderson, 1981)
2. IASP91速度模型 (Kennett and Engdahl, 1991)
Radon transform p ( s , ) f ( x , y ) ( x c y s o s ) d is n x
where p is the radon transform of f(x, y), and is a Dirac Delta Function (an infinite spike
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全球地震层.析成像
地幔柱 区域地震层. 析成像
大洋中脊 区域地震层. 析成像
俯冲带 区域地震层. 析成像
局部地震层析成像
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地震层析成像的基础——Radon 变换 Tomo— Greek for “tomos” (body), graphy --- study or subject Where it all began: Radon transform: (Johan Radon, 1917): integral of function over a straight line segment.
0
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A few of the early medical tomo setups
Parallel beam
Fan beam, Multi-receiver, Moves in big steps
Broader fan beam, Coupled, moving source receivers, fast moving
PREM模型给出了地球的一维结构，而地球内部三维结构需要更精细的刻画。 地震层析成像方法是给出地球内部三维结构的最重要的方法。 某种意义上说，地震是照亮地球内部的明灯。 地震层析成像方法可以给出：
全球地球结构的横向不均匀性； 典型地球动力学过程的三维结构：俯冲带、地幔柱、大洋中脊等； 小尺度的构造（断层等）； 地震分布特征。