Atmospheric pressure change associated with the 2003 Tokachi-Oki earthquake

Clear atmospheric pressure changes associated with the 2003 Tokachi-Oki, Japan, earthquake with Mw 8.3 were recorded with the microbarographs distributed in Japan. The pressure change starts at the arrival of seismic waves and reaches its maximum amplitude at the arrival of Rayleigh waves, suggesting that the observed pressure change was driven by the ground motion of seismic waves passing by the site. We computed the seismic-to-pressure transfer function (i.e., the spectral ratio of the pressure change to the vertical ground motion velocity) for periods between 10 to 50 s from the co-located barograph and seismograph records. 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 are explained by the acoustic coupling between the atmosphere and the ground just beneath the sensors.