Geological Investigations of Late and Post Glacial Earthquake Activity in Scotland

Abstract

Evidence for palaeoseismicity in Scotland is presented and includes evidence of: (1) Surface fault movement during late and post glacial time; (2) Soft-sediment deformation in lacustrine sediment attributable to seismic ground shaking; (3) Large landslides triggered by earthquakes. These features are located in areas asssociated with rapid post glacial uplift. Events estimated to be as large as Magnitude 6.5–7.0 occurred around 10,000 years ago and Magnitude 5.0–6.0 events as recently as 2–3000 years ago. Shallow active stress measurements indicate the presence of the dominant horizontal compressive stress in directions around 130° (NW-SE). Stress and palaeoseismic field evidence form the basis to our hypothesis for post glacial fault activity, that: (1) Long-term stress controls fault ruptures associated with glacial rebound; (2) Fracture directions are orientated close to the direction of maximum horizontal compressive stress; (3) Displacements are predominantly strike-slip and are coseismic; (4) Glacially reactivated fracture zones continue to be the sources of present-day low level seismicity; (5) Surficial displacements result from the interaction of tectonic, lithostatic and hydrostatic stresses within a “partially detached” thin upper-crustal layer associated with glacial rebound.