The underlying cause and distribution of earthquake activity in the British Isles is not clearly understood. Recent work by Baptie (2010) presents a compilation of focal mechanisms for British earthquakes that help constrain our understanding of the driving forces of present day deformation in the British Isles.
Best-fitting stress tensors determined using two different inversion methods suggest that there is a significant difference in the stress state between northwest Scotland and England and Wales. Calculated s1 directions for England and Wales are consistent both with existing stress data and expected stresses from first order plate motions. By contrast, the inversion results for northwest Scotland show near east-west extension.
The clear difference in the stress inversion results between northwest Scotland and England and Wales suggests that the principal stress directions expected from first order plate motions have been modified in Scotland by local stress conditions due to glacio-isostatic adjustment.
Baptie, B., Seismogenesis and State of Stress in the UK, Tectonophysics (2010), doi:10.1016/j.tecto.2009.10.006