Nature and origin of upper crustal seismic velocity fluctuations and associated scaling properties: Combined stochastic analyses of KTB velocity and lithology logs
Nature and origin of upper crustal seismic velocity fluctuations and associated scaling properties: Combined stochastic analyses of KTB velocity and lithology logs
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上地壳地震速度波动的性质和起源以及相关的标度特性：KTB 速度和岩性测井的组合随机分析
DOI：
10.1029/1999jb900129
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发表时间：
1999
影响因子：
--
通讯作者：
K. Holliger
中科院分区：
文献类型：
--
作者：
J. Goff;K. Holliger
德国大陆深钻计划（KTB）的主钻孔延伸超过9000米，进入主要由层间片麻岩和变质岩组成的结晶上地壳。我们对速度和岩性测井进行了联合分析，试图提取速度测井的岩性成分。对岩性测井曲线进行协方差分析，将其近似为二元序列，表明其可能来源于特征尺度分别为~ 2800 m和~ 150 m的两个布朗随机过程（分形维数为1.5）的叠加。对速度波动的协方差分析为四个具有不同特征尺度的随机过程的叠加提供了证据。最大的两个尺度与岩性计算结果相同，证实了这些速度非均质尺度是由岩性变化引起的。第三个特征尺度为~ 20 m，也是一个布朗过程，根据与电阻率测井的对比，可能与压裂有关。这三个布朗过程的叠加非常接近于通常观察到的速度功率谱的1/k衰减（分形维数2.0）。最小尺度过程（特征尺度~ 1.7 m）需要较低的分形维数（~ 1.0），占总均方根速度变化的~ 60%。6900-7140米深度连续测井的比较表明，这种变化是不可重复的，因此可能不能代表地壳中真正的速度变化。本研究的结果解决了基于KTB声波测井的不同地震非均质性估计之间的差异，并弥合了地质图和钻孔测井对地壳非均质性估计之间的差距。
The main borehole of the German Continental Deep Drilling Program (KTB) extends over 9000 m into a crystalline upper crust consisting primarily of interlayered gneiss and metabasite. We present a joint analysis of the velocity and lithology logs in an effort to extract the lithology component of the velocity log. Covariance analysis of lithology log, approximated as a binary series, indicates that it may originate from the superposition of two Brownian stochastic processes (fractal dimension 1.5) with characteristic scales of ∼2800 m and ∼150 m, respectively. Covariance analysis of the velocity fluctuations provides evidence for the superposition of four stochastic process with distinct characteristic scales. The largest two scales are identical to those derived from the lithology, confirming that these scales of velocity heterogeneity are caused by lithology variations. The third characteristic scale, ∼20 m, also a Brownian process, is probably related to fracturing based on correlation with the resistivity log. The superposition of these three Brownian processes closely mimics the commonly observed 1/k decay (fractal dimension 2.0) of the velocity power spectrum. The smallest scale process (characteristic scale ∼1.7 m) requires a low fractal dimension, ∼1.0, and accounts for ∼60% of the total rms velocity variation. A comparison of successive logs from 6900–7140 m depth indicates that such variations are not repeatable and thus probably do not represent true velocity variations in the crust. The results of this study resolve disparity between the differing published estimates of seismic heterogeneity based on the KTB sonic logs, and bridge the gap between estimates of crustal heterogeneity from geologic maps and borehole logs.