Synthesis of realistic oceanic Pn wave trains
Synthesis of realistic oceanic Pn wave trains
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真实海洋 Pn 波列的合成
DOI：
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发表时间：
1985
期刊：
影响因子：
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通讯作者：
J. Orcutt
中科院分区：
文献类型：
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作者：
Thomas S. Ereno;J. Orcutt
合成的现实海洋Pn相位完成使用波数积分。针对横向均匀、垂直不均匀的海洋岩石圈模型生成了初始压缩波到达后持续时间为100 s量级的波列。这些长波列的激发主要是近接收器水和沉积物混响的结果，不涉及散射。即使相速度限制在5.5公里/秒以上，也产生了一个群速度为1.6公里/秒的迟到波列，它具有大洋深海T相的特征，具有突发的开始和相当长的持续时间。合成Pn波列进行了比较，在西南太平洋Ngendei地震实验期间收集的数据。在合成物中观察到的与沉积物和水混响相关的许多光谱特性也在数据中观察到。首先，它被发现的Pn波列的振幅衰减率是一个强烈的频率增加的函数，在直接对比预测的结果为前向散射尾波。这导致了在波列后期低频占优势，这很容易解释为不同混响模式的建设性干扰。第二，在与沉积物和水混响的频率谱峰的存在下进行了观察。预测的频率计算使用的值的水深，沉积物厚度和沉积物的速度在一个独立的研究。与预测频率的频谱峰值的强对齐说明了Pn波列的混响性质。超过15 Hz的大量功率的存在可以归因于Pn对海洋岩石圈的限制。因此，海洋Pn相位的特点是折射从较低的岩石圈与海洋水柱和沉积层中的多次混响，包括随后的尾波。不需要复杂的海洋岩石圈模型来解释Pn传播的总体特征。
The synthesis of realistic oceanic Pn phases was accomplished using wave number integration. Wave trains with durations of the order of 100 s following the initial compressional wave arrival were generated for a laterally homogeneous, vertically inhomogeneous oceanic lithosphere model. The excitation of these long wave trains is primarily a result of near-receiver water and sediment reverberations and does not involve scattering. A late arriving wave train with a group velocity of 1.6 km/s having an emergent onset and substantial duration, characteristic of oceanic abyssal T phases, was also generated even with phase velocities restricted to be greater than 5.5 km/s. The synthetic Pn wave train was compared to data collected in the southwest Pacific during the Ngendei Seismic Experiment. Many of the spectral characteristics associated with sediment and water reverberation observed in the synthetics were also observed in the data. First, it was found that the amplitude falloff rate of the Pn wave train is a strongly increasing function of frequency, in direct contrast to results predicted for forward scattered coda. This leads to a predominance of low frequencies late in the wave train which is easily interpreted in terms of the constructive interference of different modes of reverberation. Second, the presence of spectral peaks at frequencies associated with both sediment and water reverberations was observed. The predicted frequencies were computed using values of the water depth, sediment thickness, and sediment velocity obtained in an independent study. Strong alignment of the spectral peaks with the predicted frequencies illustrates the reverberating nature of the Pn wave train. The presence of substantial power in excess of 15 Hz can be attributed to the confinement of Pn to the oceanic lithosphere. The oceanic Pn phase is thus characterized as a refraction from the lower lithosphere with multiple reverberations in the oceanic water column and sediment layer comprising the subsequent coda. Complicated oceanic lithosphere models are not needed to explain the gross characteristics of Pn propagation.