Updated intensity attenuation for the UK

For many purposes, including seismic hazard and risk calculations, it is useful to be able to
estimate the expected intensity value at a place as a function of magnitude and distance. Such a
model was published by Musson (2005), relating intensity to local magnitude and hypocentral
distance, based on a dataset comprising 727 isoseismals from 326 British earthquakes, including
both modern and historical events, up to 1 October 2002, though for the preferred equation only
a subset of this dataset was used. This update adds more data from earthquakes that have
occurred since then, up to 1 June 2013. More importantly, the model is recast in terms of
moment magnitude. The preferred result is
I = 3.50 + 1.28 Mw – 1.18 ln R
This is derived from a subset of the total dataset, discarding data for intensity 2 (poorly
constrained) and using only earthquakes with at least two isoseismals.