Impacts of non-plane waves on two-station measurements of phase velocities
Impacts of non-plane waves on two-station measurements of phase velocities
复制标题
非平面波对两站相速度测量的影响
DOI：
10.1111/j.1365-246x.2006.02893.x
复制
发表时间：
2006
影响因子：
2.8
通讯作者：
H. Pedersen
中科院分区：
文献类型：
--
作者：
H. Pedersen
为了确定岩石圈中的区域剪切波速度，经常需要使用两个站的频散曲线。我们调查非平面波能量的影响，这样的色散曲线，并将它们与其他两个更好的已知来源的错误：偏离大圆路径和不相关的噪声。为了研究远距离非均匀性产生的非平面波的影响，我们在横向均匀介质中通过向主平面波添加干涉波来创建复杂的波场。然后，我们计算位于相距100-400公里的两个地震台站之间的视相速度。使用实际值的误差来源，我们得出结论，每个的贡献是相似的200公里长的配置文件。我们关于非平面波的结论是在假定来自遥远不均匀体的非平面能量随震源位置随机变化的条件下得出的。如果这是正确的，那么只需要5到10个具有不同震源的事件就可以获得误差小于1%的稳定的频散曲线。不相关噪声和非平面波的影响减少较长的配置文件，而由于大圆偏差的错误是独立的配置文件的长度和系统的偏移频散曲线，以更高的速度。我们建议在区域尺度上纳入一些用于表面波研究的非剖面宽带台站，因为此类补充台站可以对非大圆传播进行一阶校正。不同误差来源的强烈影响，加上我们对非平面能量的性质和幅度缺乏精确的了解，意味着对两个台站测量结果的解释应限于区域地球结构的重大变化。
SUMMARY To determine the regional shear wave velocities in the lithosphere it is frequently necessary to use two-station dispersion curves. We investigate the influence of non-plane wave energy on such dispersion curves, and compare them to two other better known sources of error: deviations from great-circle paths and uncorrelated noise. To study the influence of nonplane waves created from distant heterogeneities we create complex wavefields in a laterally homogeneous medium by adding interfering waves to a main plane wave. We then calculate the apparent phase velocity between two seismic stations located 100–400 km apart. Using realistic values for the sources of error, we conclude that the contribution of each is similar for 200-km-long profiles. Our conclusions on non-plane waves are made under the assumption that non-plane energy from distant heterogeneities varies randomly with hypocentre location. If this is correct, then only five to 10 events with different hypocentres are required to obtain a stable dispersion curve with less than 1 per cent error. The influence of uncorrelated noise and non-plane waves diminish for longer profiles, while the errors due to great-circle deviations are independent of profile length and systematically bias the dispersion curve to higher velocities. We recommend the inclusion of some off-profile broad-band stations for surface wave studies on a regional scale, because such supplementary stations make it possible to apply first-order corrections for off great-circle propagation. The strong influence from the different sources of error, combined with our lack of precise knowledge of the nature and amplitude of non-plane energy, implies that the interpretation of two-station measurements should be restricted to major changes in regional earth structure.