The 1984 Llŷn Peninsula earthquake struck the Llŷn Peninsula in Gwynedd, northwest Wales on Thursday 19 July 1984 at 06:56 UTC (07:56 BST). Measuring 5.4 on the Richter scale, it is the largest onshore earthquake to occur in the UK since instrumental measurements began. The 19 July earthquake was followed by many aftershocks in the following months, the largest measuring 4.3 on the Richter scale, which itself was felt as far away as Dublin, in Ireland.