What Was the Largest British Earthquake?

The issue of “largest observed earthquake in a region” is both important for seismic hazard analysis and also of journalistic and popular interest. Identifying the relevant event is not always straightforward in intraplate regions such as the UK, where the historical earthquake catalogue is short with respect to the seismic cycle. In Britain, the largest 20th century event (i.e. instrumentally recorded) was the North Sea earthquake of 7 June 1931. However, there are several pre-instrumental earthquakes that affected Britain which may have been as large or larger. However, the task of estimating magnitude from often very scant historical accounts is difficult, and leads to much speculation. In this paper, the evidence for four such earthquakes is reviewed, but it is not possible to come to a firm conclusion regarding any of them.