Fig. 11
From: Seismic noise between 0.003 Hz and 1.0 Hz and its classification
a Co-located pressure vertical seismic data (both PSD, denoted by SP and SZ) are plotted for an EarthScope station U57A. Each point is from a one-hour time interval and data from the entire year of 2014 are plotted. Red indicates the time intervals when coherence between pressure and vertical seismic data was high (> 0.7). The threshold pressure is about 100 (Pa2/Hz); above it, local pressure and seismic vertical amplitudes become correlated. Also, high-coherence time intervals are when pressure exceeds this threshold. b Co-located wind speed and vertical seismic data are plotted. The vertical scale is the same as a. Pressure data in a were replaced by wind speed data. The vertical axis The overall similarity to a indicates that surface pressure is closely related to wind. c Frequency dependence of coherence for time intervals with pressure PSD higher than 300 (Pa2/Hz). There is a high-coherence frequency interval of approximately 0.01 Hz to 0.05 Hz, indicated by red vertical dashes. d Phase difference between pressure and vertical displacement. When pressure is high, the phase differences are about 180° (opposite phase). e An illustration of the relationship between pressure and vertical displacement. When pressure is high, the ground surface gets pushed down and vice versa. This is the manifestation of the quasi-static deformation