Small‐scale heterogeneities below the Gräfenberg array, Germany from seismic wavefield fluctuations of Hindu Kush events
Small‐scale heterogeneities below the Gräfenberg array, Germany from seismic wavefield fluctuations of Hindu Kush events
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DOI：
10.1046/j.1365-246x.2000.00013.x
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发表时间：
2000
影响因子：
2.8
通讯作者：
E. Rothert;J. Ritter
中科院分区：
文献类型：
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作者：
E. Rothert;J. Ritter
摘要在德国东南部格拉芬贝格台尼思的岩石圈上部发现了小尺度弹性不均匀性（<5 km）。这些结果是基于对兴都库什地区17个中等深度（201-272公里）事件的宽带记录的分析。在0.05 ~ 5 Hz的频率范围内，将第一波P波的波前和随后的40 s尾波分成相干和非相干（散射）部分。平均波场和起伏波场的强度随频率的变化被用来描述接收器下方岩石圈的散射特性。可以区分在低于大约1.5-2.5 Hz的频率范围内的波场的弱波动状态和在2.0-2.5 Hz开始并继续到更高频率的强波动状态。为了解释观测到的波场波动，提出了一种随机介质结构地震波散射的方法。优选的模型含有不均匀性，地震速度有3- 7%的扰动，地壳的相关长度为0.6-4.8公里。这与主动地震实验的模型是一致的。岩石圈地幔中的散射不是必需的，但在弱速度对比（<3%）时不能排除。
SUMMARY Small-scale elastic heterogeneities (<5 km) are found in the upper lithosphere under- neath the Grafenberg array, southeast Germany. The results are based on the analysis of broadband recordings of 17 intermediate-depth (201-272 km) events from the Hindu Kush region. The wavefront of the first P arrival and the following 40 s coda are separated into coherent and incoherent (scattered) parts in the frequency range from 0.05 to 5 Hz. The frequency-dependent intensities of the mean and fluctuation wavefields are used to describe the scattering characteristics of the lithosphere underneath the receivers. It is possible to discriminate a weak-fluctuation regime of the wavefield in the frequency range below approximately 1.5-2.5 Hz and a strong-fluctuation regime starting at 2.0-2.5 Hz and continuing to higher frequencies. In order to explain the observed wavefield fluctuations, an approach with seismic scattering at random media- type structures is proposed. The preferred model contains heterogeneities with 3-7 per cent perturbations in seismic velocity and correlation lengths of 0.6-4.8 km in the crust. This is compatible with models from active seismic experiments. Scattering in the lithospheric mantle is not required, but cannot be excluded at weak velocity contrasts (<3 per cent).