Determination of the three‐dimensional seismic structure of the lithosphere
Determination of the three‐dimensional seismic structure of the lithosphere
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DOI：
10.1029/jb082i002p00277
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发表时间：
1977-01
影响因子：
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通讯作者：
K. Aki;A. Christoffersson;E. Husebye
中科院分区：
文献类型：
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作者：
K. Aki;A. Christoffersson;E. Husebye
提出了一种新的三维地球模型，作为一个框架，以获得更详细和更准确的信息，关于地球的内部。我们从经典地震学的层状介质开始，但将每一层分成许多块，并为每个块分配一个参数，该参数描述了该层平均速度的波动。我们的数据是在我们正在建模的地球体积上方的表面上分布的地震仪阵列上观察到的P2P走时残差。通过隔离各种来源的误差和偏见，我们到达一个方程组，以确定模型参数。利用广义逆和随机逆方法求解。在射线理论的假设下，我们的方法也给出了地球真均方根慢度起伏的下限。利用挪威地震台阵（Norsar）的P波剩余资料，我们得到了126公里以下不同深度的速度异常图。均方根慢度波动被认为是至少3.1%。这是在协议的基础上的P时间波动的统计分析获得的估计。三维速度异常分别由广义逆解和随机逆解表示。我们更喜欢双重的介绍，因为它给读者更大的自由，在判断结果比一个单一的“最佳”的解决方案。两种方法得到的结果基本相同。当存在差异时，总是可以用分辨率矩阵中明确给出的平滑过程中的差异来解释。在Norsar阵列下方获得的岩石圈三维速度图像的主要特点是低速向西和高速向东。后一个特征可能归因于波罗的海地盾的岩石，这些岩石未受加里东造山运动或二叠纪火山活动的影响。我们的结果最终证明了岩石圈底部存在强烈的小尺度不均匀性。需要更多的理论和实验工作，将这些速度异常与导致奥斯陆地堑的岩浆上升机制联系起来。
A new three-dimensional earth modeling is proposed as a framework to obtain more detailed and accurate information about the earth's interior. We start with a layered medium of classic seismology but divide each layer into many blocks and assign a parameter to each block which describes the velocity fluctuation from the average for the layer. Our data are the teleseismic P travel time residuals observed at an array of seismographs distributed on the surface above the earth's volume we are modeling. By isolating various sources of errors and biases we arrive at a system of equations to determine the model parameters. The solution was obtained by the use of generalized inverse and stochastic inverse methods. Our method also gives a lower limit of the true rms slowness fluctuation in the earth under the assumption of ray theory. Using P wave residual data from the Norwegian Seismic Array (Norsar), we have obtained the map of velocity anomalies at various depths up to a depth of 126 km. The rms slowness fluctuation was found to be at least 3.1%. This is in agreement with estimates obtained from statistical analysis of P time fluctuations based on the Chernov theory. The three-dimensional velocity anomalies are presented both by the generalized inverse and by the stochastic inverse solutions. We prefer the dual presentation because it gives the reader greater freedom in judging the results than a single ‘optimal’ solution. Both methods gave essentially the same results. The discrepancies, when they existed, were always explainable in terms of differences in the smoothing procedure which is explicitly given in the resolution matrix. The dominant features in the obtained three-dimensional velocity image of the lithosphere beneath the Norsar array are low velocities to the west and high velocities to the east. The latter feature may be attributed to rocks of the Baltic shield which are undisturbed by the Caledonian orogeny or by Permian volcanism. Our result conclusively demonstrates the existence of strong small-scale inhomogeneities to the bottom of the lithosphere. More theoretical and experimental works are needed to relate these velocity anomalies with the magma ascent mechanism which caused the Oslo graben.