西太平洋台风对上海地区钻孔应变的低频扰动特征分析

Low-frequency Disturbance Characteristics of the Western Pacific Typhoons on the Borehole Strain in Shanghai Area

基于上海佘山台四分量钻孔应变仪在6次西太平洋台风期间的观测记录,利用小波分解、优势振动方向等处理方法提取出台风所激发的显著低频扰动信号,并详细分析扰动信号在时频域及空间域的表现特性。结果显示:在低频区间,台风激发的扰动信号优势周期为2~4 min,信号能量随台风进程而变化,并主要与台风量级、台风中心的位置(海上或陆域)及其与台站间的距离有关。在台风中心不断逼近海岸时,佘山台4个分量记录的扰动信号均开始增强,但不同方向记录的信号强度存在较显著的差别,其中振动强度最大的方向(即优势振动方向)为160°,该方向与台站所处海岸线的走向密切相关。最后结合扰动信号的时频及空间响应特征,对比地表风速、海洋浮标记录后认为分量应变仪记录的低频扰动信号与近海浪高的相关性较好;综合信号的频谱特征,认为应变仪记录的台风扰动信号是由近岸浅海区域的海洋长重力波激发产生的。

Based on the records of four-component borehole strain gauge of Sheshan station in Shanghai during the six western Pacific typhoons,the methods of wavelet decomposition and predominant polarization direction were applied to extract the significant low-frequency disturbance signals excited by the typhoon,and the characteristics of disturbance signal in time-frequency domain and spatial domain were then analyzed in detail.The results showed that in the low frequency range,the dominant period of disturbance signal excited by the typhoon is 2-4 min;the signal energy varies with the progress of typhoon,and is mainly related to the magnitude of typhoon,the location of typhoon center(sea or land),and the distance between the station and the typhoon center.As the typhoon center approached the coast,the disturbance signals recorded by the four components of Sheshan station began to increase,but the signal intensity recorded in different directions were not consistent.The predominant polarization direction of the signal is 160°and closely related to the strike of the coastline where the station is located.Finally,based on the time-frequency and spatial response characteristics of the disturbance signal,and the records of surface wind speed and ocean buoy,it is considered that the low-frequency disturbance signal recorded by the component strain gauge has a good correlation with the offshore wave height,and the typhoon disturbance signal recorded by the strain gauge is generated by the infragravity waves from the offshore area.