The influence of wind on measurements of seismic noise

The horizontal to vertical spectral ratio (HVSR) technique of microtremor measurement is widely applied in microzonation and site response studies. Given the small amplitude of the measured signal, unwanted disturbances may adversely affect the results. We analysed the influence of local wind on microtremor measurements as follows: first, we studied variation in HVSR at a permanent, three-component seismological station under various wind patterns; second, we conducted an experiment under controlled condition in a wind room equipped with a laser particle image velocimeter, analysing the effect of increasing wind speed on various sensor/digitizer configurations; third, we undertook numerical modelling to explain the observed data. Our main conclusions are that wind increases the amplitude of all components of the microtremor wavefield, but does not affect HVSR; however, certain sensor/digitizer configurations can be adversely affected by instrumental noise due to turbulence at the air/instrument/ground interface.