What are the largest two instrumental, onshore earthquakes?
The 19 July 1984 Lleyn event of North Wales, with a magnitude of 5.4 ML, was the largest onshore earthquake this century in the UK and was felt over an area of around 240,000 square kilometres. The earthquake occurred in the lower crust at a depth of approximately 22 km and was followed by many aftershocks. Detailed mapping of the aftershock distribution highlighted a plane orientated WNW-ESE and dipping steeply NNE. This represents the fault plane and corresponds well with one of the planes of the mainshock focal mechanism. There is, however, no surface fault or feature which corresponds to this plane. The maximum intensity in the epicentral area was 6 EMS (European macroseismic scale) and damage consisted of widespread cracks in plaster and falls of some chimneys and weak plaster. High intensities of 5 and 6 EMS reported from Liverpool appear to be due to the state of repair of some of the buildings. The 2 April 1990 Bishop’s Castle earthquake in the Welsh Borders, with a magnitude o
