The complexity of modelling anisotropic intensity attenuation in Belgium
(2021) 37th General Assembly of the European Seismological Commission — Location: Online (19.September.2021)
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- Authors
Neefs, Ben 
- et. al.
- Abstract
- The traditional methodology of constructing a single intensity attenuation law and intensity prediction equation for large areas is not fit for the complex situation in Belgium. Macroseismic intensity distribution patterns of past Belgian earthquakes do not cohere to the common assumption of an isotropic intensity decrease with increasing epicentral distance. Intensity decrease is strongly influenced by crustal and cover geological features that heavily control and limit seismic wave propagation. Geological features that have influenced past intensity distribution patterns in NW Europe are: - The strongly compacted and deformed Lower Palaeozoic Anglo-Brabant Massif, which easily transfers ground motion along its core axis in a WNW-ESE direction. - The increasing thickness of soft sedimentary Cenozoic strata covering the Anglo-Brabant massif towards the Belgium-The Netherlands border, effectively filtering high-frequency ground motions. - The Lower Rhine Embayment boundary faults, impeding effective ground motion transfer and serving as seismic mirrors. - The Midi-Eifel Fault which separates the Ardenne allochton from its foreland and acts as a seismic barrier. - A band of shallow Carboniferous coal basins with a fast intensity attenuation. The quantitative effect of these geological regions on macroseismic intensity are best to be modelled separately. But given the small size of both Belgium and these different regions, local earthquakes are prone to hit multiple areas with different attenuation properties at once, urging the necessity of transfer functions from one unit to another. Moreover, anisotropic intensity attenuation laws are very uncommon in literature and adding another dimension, e.g. such as bedrock depth, into an intensity prediction equation complicates the modelling even more. During this presentation, these PhD issues and topics will be discussed by using the extensive traditional and online macroseismic intensity databases of the Royal Observatory of Belgium, which was extended by macroseismic intensity data from neighboring countries.
- Affiliations
Royal Observatory of Belgium
Citations
Neefs, B., & et al. (2021). The complexity of modelling anisotropic intensity attenuation in Belgium. 37th General Assembly of the European Seismological Commission, Online. https://hdl.handle.net/2078.5/217295