Global adjoint tomography: first-generation model
Global adjoint tomography: first-generation model
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DOI：
10.1093/gji/ggw356
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发表时间：
2016-12-01
影响因子：
2.8
通讯作者：
Pugmire, David
中科院分区：
文献类型：
--
作者：
Bozdag, Ebru;Peter, Daniel;Pugmire, David
我们提出了第一代全球层析成像模型的基础上构建的伴随层析成像，迭代全波形反演技术。使用GPU加速的谱元模拟全球地震波传播计算合成地震图，适应由于3-D滞弹性地壳和地幔结构，地形和测深，海洋负荷，椭圆度，旋转和自引力的影响。在三维滞弹性模型中，采用伴随状态法计算了Fr、Chet导数。模拟是在名为“泰坦”的Cray XK 7上进行的，这是一台拥有18 688个GPU加速器的计算机，位于橡树岭国家实验室。横向各向同性的全球模型是15次层析迭代的结果，系统地减少了观测和模拟三分量地震图之间的差异。我们的初始模型结合了三维地幔模型S362 ANI和三维地壳模型Crust2.0。我们同时反演地壳和地幔的结构，从而消除了广泛使用的“地壳校正”的需要。我们使用了253次地震的数据，震级范围为5.8 a千分之一M-w a千分之7.0。我们通过将类似于30 s的体波数据与类似于60 s的面波数据相结合来开始反演。表面波的最短周期逐渐减小，在最后三次迭代中，我们将类似于17 s的体波与类似于45 s的表面波相结合。在第12次迭代后，我们开始使用180分钟长的地震记录，并同化了次要和主要弧体波和面波。第15次迭代模型的特点是增强了著名的板块，增强了萨摩亚/塔希提烟羽的图像，以及其他各种烟羽和热点，如卡罗琳、加拉帕戈斯、黄石和埃里伯斯。此外，我们看到了明显的改善板块分辨率沿着希腊和日本弧，以及俯冲沿着东部的斯科舍板块，这是不存在的初始模型。点扩散函数测试表明，我们正在接近在某些地区，例如，黄石公园下面的大陆尺度研究的分辨率。这是我们的多尺度平滑策略的结果，在该策略中，我们将平滑算子定义为近似Hessian内核的函数，从而在光线覆盖良好的地方（例如北美下方）平滑梯度。
We present the first-generation global tomographic model constructed based on adjoint tomography, an iterative full-waveform inversion technique. Synthetic seismograms were calculated using GPU-accelerated spectral-element simulations of global seismic wave propagation, accommodating effects due to 3-D anelastic crust & mantle structure, topography & bathymetry, the ocean load, ellipticity, rotation, and self-gravitation. Fr,chet derivatives were calculated in 3-D anelastic models based on an adjoint-state method. The simulations were performed on the Cray XK7 named 'Titan', a computer with 18 688 GPU accelerators housed at Oak Ridge National Laboratory. The transversely isotropic global model is the result of 15 tomographic iterations, which systematically reduced differences between observed and simulated three-component seismograms. Our starting model combined 3-D mantle model S362ANI with 3-D crustal model Crust2.0. We simultaneously inverted for structure in the crust and mantle, thereby eliminating the need for widely used 'crustal corrections'. We used data from 253 earthquakes in the magnitude range 5.8 a parts per thousand M-w a parts per thousand 7.0. We started inversions by combining similar to 30 s body-wave data with similar to 60 s surface-wave data. The shortest period of the surface waves was gradually decreased, and in the last three iterations we combined similar to 17 s body waves with similar to 45 s surface waves. We started using 180 min long seismograms after the 12th iteration and assimilated minor- and major-arc body and surface waves. The 15th iteration model features enhancements of well-known slabs, an enhanced image of the Samoa/Tahiti plume, as well as various other plumes and hotspots, such as Caroline, Galapagos, Yellowstone and Erebus. Furthermore, we see clear improvements in slab resolution along the Hellenic and Japan Arcs, as well as subduction along the East of Scotia Plate, which does not exist in the starting model. Point-spread function tests demonstrate that we are approaching the resolution of continental-scale studies in some areas, for example, underneath Yellowstone. This is a consequence of our multiscale smoothing strategy in which we define our smoothing operator as a function of the approximate Hessian kernel, thereby smoothing gradients less wherever we have good ray coverage, such as underneath North America.