Research project MO/33/016 (Research action MO)
A recent study has shown that, in certain regions of Belgium, local geological conditions may have a decisive influence on ground movements felt during a seismic event. Conducted by the ORB in collaboration with the University of Liège, this study prompted the seismology division to extend its investigation to local site effects with a view to identifying seismic response in terms of 1) resonance frequency and 2) amplification of a given site.
We propose to develop the method based on recording and analysis of seismic noise (H/V method) to derive the resonance frequency of a site. The H/V spectrum derived from the spectral ratio between the horizontal components and the vertical component of a noise recording, often includes an amplitude peak at a given frequency. The latter generally characterises the fundamental resonance mode of the site under investigation, directly related to the thickness of soft soils and the rate of propagation of shear waves in these soils. This methodology, which is being developed initially in the context of studies conducted in the Brabant Massif and Mons Basin, will be automated and integrated into the day-to-day activities of the Belgian Royal Observatory.
To determine the amplitude of site effects, we propose to develop numerical simulation tools to calculate transfer functions in the case of one or two-dimensional geological structures and for different plausible seismic scenarios in Belgium.
