The frequency dependence and locations of short‐period microseisms generated in the Southern Ocean and West Pacific
The frequency dependence and locations of short‐period microseisms generated in the Southern Ocean and West Pacific
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DOI：
10.1002/2015jb012210
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发表时间：
2015-08
期刊：
影响因子：
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通讯作者：
M. Gal;A. Reading;S. Ellingsen;L. Gualtieri;K. Koper;R. Burlacu;H. Tkalčić;M. Hemer
中科院分区：
文献类型：
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作者：
M. Gal;A. Reading;S. Ellingsen;L. Gualtieri;K. Koper;R. Burlacu;H. Tkalčić;M. Hemer
微地震波场的起源与深海和沿海地区有关，在这些地区，在某些条件下，海浪可以激发作为面波和体波传播的地震波。考虑到地震信号的特征通常随频率而变化，这里我们探索在澳大利亚中等口径(25公里)阵列上记录的微震的频率和方位相关特性。我们研究了波场的频率相关特性及其在二十年(1991年至2012年)中的时间变化，重点是在沃拉蒙加阵列记录的相对较高频率(0.325-0.725赫兹)的微震，该阵列在该频率范围内具有良好的慢度分辨率。分析是使用非相干平均信号Capon波束形成进行的，该波束形成给出了对慢度和后方位角的稳健估计，并且能够在单个时间窗口内分辨多个波到达。对于面波，我们发现，在较低频率(0.55赫兹)占主导地位的基模瑞利波(Rg)表现出向较高模面波(Lg)的转变。对于体波，对于低频，震源位置确定在深海区域，对于高频，震源位置确定在浅海。我们进一步研究了面波到达和WaveWatch III海浪后播之间的联系。与海浪后播的相关分析表明，低频段的次生微震主要是由海浪涌浪引起的，而高频段的次生微震主要是由海风引起的，即局地风条件。
The origin of the microseismic wavefield is associated with deep ocean and coastal regions where, under certain conditions, ocean waves can excite seismic waves that propagate as surface and body waves. Given that the characteristics of seismic signals generally vary with frequency, here we explore the frequency‐ and azimuth‐dependent properties of microseisms recorded at a medium aperture (25 km) array in Australia. We examine the frequency‐dependent properties of the wavefield, and its temporal variation, over two decades (1991–2012), with a focus on relatively high‐frequency microseisms (0.325–0.725 Hz) recorded at the Warramunga Array, which has good slowness resolution capabilities in this frequency range. The analysis is carried out using the incoherently averaged signal Capon beamforming, which gives robust estimates of slowness and back azimuth and is able to resolve multiple wave arrivals within a single time window. For surface waves, we find that fundamental mode Rayleigh waves (Rg) dominate for lower frequencies (0.55 Hz) show a transition to higher mode surface waves (Lg). For body waves, source locations are identified in deep ocean regions for lower frequencies and in shallow waters for higher frequencies. We further examine the association between surface wave arrivals and a WAVEWATCH III ocean wave hindcast. Correlations with the ocean wave hindcast show that secondary microseisms in the lower‐frequency band are generated mainly by ocean swell, while higher‐frequency bands are generated by the wind sea, i.e., local wind conditions.