【摘要】 大气压力变化可分为由日、月引力和太阳热辐射产生的潮汐变化和非潮汐频段的短周期气压变化,其引起的地壳应变可达10-9量级.我们选用分钟采样的观测精度达10-9量级的钻孔应变仪,对山东省泰安台2002~2005年气压及体应变分钟值资料进行深入分析,研究了地壳应变场对短周期气压变化的响应规律.频谱分析结果表明,短周期气压变化对体应变的影响主要集中在周期大于2000 s的低频段.利用小波分解方法,得出了短周期气压系数随不同频段和不同时间的变化规律:高频段(周期小于960 s)气压系数数值较小,随频率变化幅度较大;低频段(周期大于960 s)气压系数数值较大,但变化趋于平稳;在频段一定的情况下,短周期气压系数随时间变化较平稳.从钻孔应变仪观测原理和按余弦函数分布的载荷作用于地壳表面的应力解出发,得出了地壳不同深度对不同频率短周期气压场的响应,理论计算与实际观测基本相符.研究结果表明,短周期气压变化对低频信号(周期大于2000 s)的影响较大,提取低频地球自由振荡信号时要消除气压影响,对苏门答腊大地震激发的地球球型自由振荡的功率谱分析验证了这一结论.更多还原

【Abstract】 Atmospheric pressures,which can produce crustal strain of 10-9,can be divided into atmospheric tides and short-period variations.Borehole strain observations with minute sampling at the Tai’an observation station,Shan-Dong province from 2002 to 2005 are applied to analyze the response rule of the crustal strain field to short-period atmospheric pressure variations.Spectrum analysis shows short-period atmospheric pressure variations can influence low-frequency volume strain observations(periods are greater than 2000s).Wavelet transform is used to obtain the short-period atmospheric pressure variation rule with different frequencies and different times.High-frequency atmospheric pressure coefficients,whose periods are less than 960s,are small,but variation ranges are large.Low-frequency atmospheric pressure coefficients(period greater than 960s) are large,but variation ranges are small.Atmospheric pressure coefficients with certain frequencies change reposefully.Based on the borehole strainmeter design principle and elasticity mechanics theory in which stress is distributed as a cosine function,we obtain the response rule of crust at different depth to different frequency short-period atmospheric pressure variations.Theoretical calculation is coincident with the observation curve.Research results show short-period atmospheric pressure variations can influence low-frequency signals(period greater than 2000s),thus atmospheric pressure variations must be removed when earth free oscillation signals being extracted.Earth free oscillations excited by the great Sumatra earthquake occurred on December 26,2004 that we extracted testify this conclusion.更多还原