佘山台四分量钻孔应变仪记录的台风扰动特征分析

通过对佘山台四分量钻孔应变仪在台风“浣熊”(Neoguri)和“海葵” (Haikui)经过期间所记录的信号进行小波分解、连续频谱分析以及优势振动方向计算，监测到台风对近岸造成显著低频扰动，并分析了扰动信号在时间空间频率域的影响特征，在此基础上探讨了扰动的激发机制.分析结果显示:在台风发育过程中，覆盖周期为2—16分钟的3个频段能量呈现显著的上升—峰值—下降规律，且这种升降变化与台风中心到台站之间的距离具有良好的相关性，其中周期2—4分钟为扰动的优势频段，能量幅值则随周期的增大而不断减弱.四分量钻孔应变仪在两次台风逼近期间的优势振动方向均为160°左右.通过对比风速数据，结合海岸地形，认为风对陆地的作用并不是引起低频扰动的主要原因，更可能是台风以海浪为介质，通过不断与呈光滑凹形形态的杭州湾北部海岸线的反射作用，进而激发自由振荡频段的低频扰动信号. 

Signatures of typhoons on strain records of four-component borehole strain meter at Sheshan station

In order to analyze the temporal and spatial signatures of typhoons on strain records, we processed the strain data of four-component borehole strain meter (FCBS for short) at Sheshan station during the impacting periods of typhoons "Neoguri" and "Haikui". We integrated methods of wavelet decomposition, continuous spectral analysis and predominant polarization direction to investigate the influence of ocean storms on low-frequency noise. The results show that the process of typhoon development had significantly influenced spectrum amplitudes, which showed an "increase--peak--decrease" pattern, especially over the frequency band 2--4 min. This pattern was highly correlated with the distance between the station and the center of typhoon. And with the increases of the periods, the amplitude of the spectra decreased. When the storm center was approaching to the station, the predominant polarization directions of the strain records were concentrated on the southeast of 160°, which indicates that local coastlines may play an important role in the noise excitation mechanism. The comparison of the mean spectra amplitudes with the wind speed showed that the wind was not the major excitation factor. Finally we come to the conclusion that during the typhoon development, the energy of ocean waves greatly increases, and the waves with higher energy are continuously lapping at the shore, which results in low-frequency disturbances on continents.