Existence of the threshold pressure for seismic excitation by atmospheric disturbances

Excitation of seismic waves by atmospheric pressure changes is examined from data for two tropical cyclones, Tropical Storm Lee (2011) and Hurricane Isaac (2012). They moved through the EarthScope Transportable Array and generated variations in pressure and ground motions that spanned 4-5 orders of magnitude in power spectral density (PSD). For vertical seismic ground velocity PSD (S-V) for frequencies between 0.01 and 0.02 Hz, there is a threshold pressure at about pressure PSD (S-P) of 10Pa(2) s, below which vertical motion is not affected by local atmospheric pressure. Above this threshold pressure, vertical ground motion increases with surface pressure as S-V similar to S-P(1.5). In order to understand the land-atmosphere interaction, pressure above this threshold is the only useful range. Horizontal component PSDs are about 2 orders of magnitude larger than vertical component PSDs and change with pressure for its entire range. This overall trend is most likely caused by ground tilt.