Intensity‐attenuation and magnitude‐intensity relationships for northwest european earthquakes

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Abstract
This study shows that, for Northwest Europe, an intraplate region of subdued seismicity, a comparatively simple attenuation model is adequate to predict quite accurately the fall‐off of intensity with distance. The analysis shows that focal depths determined from macroseismic data are confined in the upper 25 km, and that shallow shocks attenuate far more rapidly than deeper events. There is no evidence for a regional variation of the absorption coefficient, which, together with the coefficient of geometric spreading, is a function of depth. Also, the intensity factor b, which is usually taken to be equal to 3, is a variable and a function of the energy absorption at the epicentre. It is shown that magnitudes can be predicted accurately by use of one or preferably by more isoseismal radii calibrated against re‐assessed instrumental magnitudes.