On reduction of long-period horizontal seismic noise using local barometric pressure

Tilt from atmospheric loading has long been known to be the major source of long-period horizontal seismic noise. We try to quantify these effects for seismic data from the Black Forest Observatory (BFO), which is known to be a very quiet station. Experimental transfer functions between local barometric pressure and horizontal seismic noise are estimated for two long time-series by standard methods. Two simple analytical physical models are developed: the local deformation model (LDM) and the acoustic-gravity wave model (TWM). Subsequently these models, with only two free parameters are fit using least squares to the observed seismic noise for time-series of widely differing lengths. The results are variable, sometimes rather dramatic variance reductions are obtained and sometimes the reduction is hardly significant. The method produces the best results when barometrically induced noise is high. The resulting admittances for the LDM are compared to finite element calculations. Since the methods are simple and can result in conspicuous reductions in noise we provide one more reason for installing barometers at even the best broad-band seismic stations.