Neefs, Ben ; Van Noten, Koen ; Camelbeeck, Thierry

Talk presented at 37th General Assembly of the European Seismological Commission on 2021-09-23

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 epicentral distance. Intensity decrease is strongly influenced by crustal and cover geological features in the subsurface that heavily control and limit seismic wave propagation. Geological features that have influenced past intensity distribution patterns 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 Eifel-Midi Fault which acts as a seismic barrier. -A band of shallow coal basins across the country in an east - west orientation 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 database of the Royal Observatory of Belgium (ROB), which was extended with macroseismic intensity data from neighboring countries.

Keyword(s): Macroseismology, intensity prediction equation, ground motion attenuation
Funding: PhD ROB funding/PhD ROB funding/PhD ROB funding