A Bayesian 3-D linear gravity inversion for complex density distributions: application to the Puysegur subduction system
A Bayesian 3-D linear gravity inversion for complex density distributions: application to the Puysegur subduction system
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DOI：
10.1093/gji/ggaa425
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发表时间：
2020-09
影响因子：
2.8
通讯作者：
E. Hightower;M. Gurnis;H. V. Van Avendonk-H.-V.-Van Avendonk-2126539230
中科院分区：
文献类型：
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作者：
E. Hightower;M. Gurnis;H. V. Van Avendonk-H.-V.-Van Avendonk-2126539230
我们已经开发出一种线性三维重力反演方法，能够模拟复杂的地质区域，如俯冲边缘。我们的程序反演卫星重力，以确定空间离散的地下棱镜在最小二乘意义上的最佳拟合的微分密度。我们使用贝叶斯方法，将数据误差和先验约束的基础上，地震反射和折射数据。基于这些数据，高斯先验被应用到适当的模型参数作为绝对等式约束。为了稳定反演并提供对参数的相对相等约束，我们利用一阶和二阶Tikhonov正则化的组合，其在地震约束区域之间的水平方向上强制平滑，同时允许在垂直方向上更尖锐的接触。我们将这种方法应用到新生的Puysegur海沟，新西兰南部，澳大利亚板块的海洋岩石圈下冲Puysegur岭和Solander盆地的太平洋板块自中新世以来。这些模型提供了深入了解该地区的密度对比，莫霍面深度和地壳厚度。最终模型的模型参数的平均标准偏差约为17千克m-3，预测重力的平均绝对误差约为3.9 mGal，证明了这种方法对于俯冲带等复杂密度分布的成功。后密度分布与地震速度是诊断成分和结构的变化，并显示了薄银的海洋地壳之间的新生逆冲断层和走滑Puysegur故障。然而，位于斯奈尔斯区的普伊塞古尔海脊北方端主要是有浮力的大陆地壳，尽管它相对于海脊其他部分下沉。这些特征突出了俯冲开始过程中的机械变化。
We have developed a linear 3-D gravity inversion method capable of modelling complex geological regions such as subduction margins. Our procedure inverts satellite gravity to determine the best-fitting differential densities of spatially discretized subsurface prisms in a least-squares sense. We use a Bayesian approach to incorporate both data error and prior constraints based on seismic reflection and refraction data. Based on these data, Gaussian priors are applied to the appropriate model parameters as absolute equality constraints. To stabilize the inversion and provide relative equality constraints on the parameters, we utilize a combination of first and second order Tikhonov regularization, which enforces smoothness in the horizontal direction between seismically constrained regions, while allowing for sharper contacts in the vertical. We apply this method to the nascent Puysegur Trench, south of New Zealand, where oceanic lithosphere of the Australian Plate has underthrust Puysegur Ridge and Solander Basin on the Pacific Plate since the Miocene. These models provide insight into the density contrasts, Moho depth, and crustal thickness in the region. The final model has a mean standard deviation on the model parameters of about 17 kg m–3, and a mean absolute error on the predicted gravity of about 3.9 mGal, demonstrating the success of this method for even complex density distributions like those present at subduction zones. The posterior density distribution versus seismic velocity is diagnostic of compositional and structural changes and shows a thin sliver of oceanic crust emplaced between the nascent thrust and the strike slip Puysegur Fault. However, the northern end of the Puysegur Ridge, at the Snares Zone, is predominantly buoyant continental crust, despite its subsidence with respect to the rest of the ridge. These features highlight the mechanical changes unfolding during subduction initiation.