Study of the atmospheric pressure change as a n excitation source of ground motion by the co-located array of microbarographs and broadband seismographs

在宫城的江之岛、茨城的筑波、千叶的野木山、宫城的雾岛、高知的室户、山科的杉野和静冈的中津，安装在日本岛沿着的微气压计记录到了与2003年十胜冲木8.3级地震相关的微小但清晰的气压变化。压力变化在地震波到达时开始，并在瑞利波到达时达到其最大幅度。地面运动约为5 mm/sec，压力变化约为2 Pa。压力记录的主要周期约为10至15秒。气压图和地震图中的波的传播速度都约为3.2公里/秒。从共置气压计和地震仪记录中构造了10秒至50秒期间垂直地面运动和压力变化之间的传递函数。传递函数表明，压力变化与垂直地面速度成正比。比较所观察到的传递函数与理论的一个，包括有限的频率和波长效应的重力分层等温大气证实，所观察到的振幅和相位的压力变化是由大气和地面之间的声耦合的传感器下面。

Small but clear atmospheric pressure changes associated with the 2003 Tokachi-Oki earthquake with M 8.3 were recorded by the microbarographs installed along Japanese Island ; at Enoshima in Miyagi, Tsukuba in Ibaragki, Nokogiriyama in Chiba, Kirishima in Miyagaki, Muroto in Kochi, Sugeno in Yamashina, and Nakaizu in Shizuoka. The pressure change starts at the arrival of seismic waves and reaches its maximum amplitude at the arrival of Rayleigh waves. The ground motion is about 5 mm/sec and pressure change is about 2 Pa. The dominant period in the pressure record is about 10 to 15 seconds. The propagation speed of the waves in barograms and seismograms are both about 3.2 km/sec. The transfer function between the vertical ground motion and the pressure change for periods between 10 sec through 50 sec is constructed from the co-locating barograph and seismograph records. The transfer function reveals that the pressure change is propotinal to the vertical ground velocity. Comparison of the observed transfer function with the theoretical one including the finite frequency and wavelength effects for a gravitationally stratified isothermal atmosphere confirms that the observed amplitude and phase of the pressure change is explained by the acoustic coupling between the atmosphere and the ground just beneath the sensors.