Long-period seafloor seismology and deformation under ocean waves
Long-period seafloor seismology and deformation under ocean waves
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发表时间：
1999-12
影响因子：
3
通讯作者：
S. Webb;W. Crawford
中科院分区：
文献类型：
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作者：
S. Webb;W. Crawford
在0.001 ~ 0.04 Hz波段，海底在长周期海浪荷载作用下的变形使深海底垂直分量噪声水平比良好大陆站点的噪声水平高20 ~ 30 dB。这种噪声极大地限制了海底地震仪观测到的长周期地震的探测阈值和信噪比。由于变形信号随深度衰减缓慢，因此只有当传感器安装在海底以下1公里以上时，钻孔安装才能显著提高信噪比。然而，利用差压计观测到的海底压力波动，可以预测和抑制垂直分量变形信号。将海浪压力观测与垂直加速度与压力传递函数测量相结合，预测海浪垂直分量的变形信号。从压力观测中减去预测的变形信号，可以将0.01 Hz附近的垂直分量噪声水平降低25 dB以上，显著提高长周期相位的信噪比。也有水平分量的变形信号，但它比垂直分量的信号小，而且只在浅水(
Abstract The deformation of the seafloor under loading by long-period ocean waves raises vertical component noise levels at the deep seafloor by 20 to 30 dB above noise levels at good continental sites in the band from 0.001 to 0.04 Hz. This noise substantially limits the detection threshold and signal-to-noise ratio for long-period phases of earthquakes observed by seafloor seismometers. Borehole installation significantly improves the signal-to-noise ratio only if the sensor is installed at more than 1 km below the seafloor because the deformation signal decays slowly with depth. However, the vertical-component deformation signal can be predicted and suppressed using seafloor measurements of pressure fluctuations observed by differential pressure gauges. The pressure observations of ocean waves are combined with measurements of the transfer function between vertical acceleration and pressure to predict the vertical component deformation signal. Subtracting the predicted deformation signal from pressure observations can reduce vertical component noise levels near 0.01 Hz by more than 25 dB, significantly improving signal-to-noise ratios for long-period phases. There is also a horizontal-component deformation signal but it is smaller than the vertical-component signal and only significant in shallow water (