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Detection of background acoustic free oscillations and development of a theory of background free oscillations in the system of the solid Earth and the atmosphere

固体地球和大气系统中背景声自由振荡的探测和背景自由振荡理论的发展

基本信息

批准号：
13304034
负责人：
FUKAO Yoshio
金额：
$ 32.95万
依托单位：
The University of Tokyo
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (A)
财政年份：
2001
资助国家：
日本
起止时间：
2001 至 2003
项目状态：
已结题

项目摘要

In an eventual aim to detect background long period acoustic waves in the atmosphere that have to be excited incessantly by the same sources as for background free oscillations of the solid Earth, we installed a cross array of barometers in a 10 km--wide university forest in central Honshu. The array has 28 micro--barometers employing quartz crystal resonator technology with a station spacing of about 500 m. We analyzed 1-second continuous sampling records in a time period from March 2002 to November 2003 to obtain one--dimensional frequency--wavenumber spectra and two-dimensional frequency--slowness spectra to detect three kinds of waves in the seismic band from 1 mHz to 0.5 Hz. We measured the dispersion curves of these waves with an assumption of stochastic stationary plane waves. The waves we detected are (1)background internal gravity waves traveling from northwest at frequencies from 1 to 5 mHz with a phase velocity of about 50 m/s, (2)background acoustic waves traveling from nor … More thwest at frequencies from 0.01 to 0.1 Hz with a frequency-dependent phase velocity of about 400 m/s at 0.1 Hz and about 1000 m/s at 0.01 Hz, and (3)microbaroms traveling from southeast at frequencies from 0.1 to 0.5 Hz with a phase velocity of about 350 m/s. Internal gravity waves (1) dominate over the random component of atmospheric turbulence in the relevant frequency range. At higher frequencies the random component with coherent length shorter than 500m is dominant. Background acoustic waves (2) show clear annual variation with maxima in winter. The annual variation and their incident azimuths suggest their possible origins in mountain regions. Microbaroms (3) are most likely to be excited by standing ocean waves in nearby coastal regions. The power spectra of these acoustic waves were compared to the seismic spectra obtained in the same university forest. Their spectral shapes are mutually similar and change commonly with variable weather conditions, indicating that the microbaroms and microseisms have their common origins. Less

为了最终探测大气中的背景长周期声波，这些声波必须由与固体地球的背景自由振荡相同的源持续激发，我们在本州中部的一个10公里宽的大学森林中安装了一个十字气压计阵列。该阵列有28个微气压计，采用石英晶体谐振器技术，站距约500m，分析了2002年3月至2003年11月一秒钟的连续采样记录，获得了一维频率波数谱和二维频率慢度谱，在1 MHz~0.5 Hz的地震频带内探测到了三种波。在随机驻波平面波的假设下，我们测量了这些波的频散曲线。我们探测到的波是(1)从西北方向传播的1-5兆赫频率的背景内重力波，相速度约为50米/S；(2)从NOR…传播的背景声波(3)从东南方向来的微气压在0.1~0.5赫兹频率范围内传播，相速度约为350m/S，重力内波(1)在相应频率范围内占主导地位。在较高频率，相干长度小于500m的随机分量占主导地位。背景声波(2)在冬季表现出明显的年最大值变化。年变化和它们的入射方位表明它们可能起源于山区。微型气球(3)最有可能被附近沿海地区的静止海浪激发。将这些声波的功率谱与在同一大学森林中获得的地震谱进行了比较。它们的光谱形状相互相似，并随着天气条件的变化而共同变化，表明微气压和微震有其共同的起源。较少