Rockall trough: Crustal structure of a complex environment from composite seismic surveys

Abstract

Coincident seismic reflection sonobuoy wide angle reflection and refraction and expanding spread refraction data have been used to study the structure of the central Rockall Trough, located on the northwest continental margin of the United Kingdom. A deep multichannel seismic reflection profile across this bathymetric defile is used to define and control the structural model, which exhibits strong contamination by Tertiary dikes and sills beneath which lies a deeper faulted, locally layered unit. Sonobuoy and expanding spread wide angle reflection and refraction data recorded along the profile allow independent determination of velocity structure by travel time tau p and linear velocity moveout calculations. An integrated model is constructed layer by layer from the surface down to Moho. Two separate sedimentary layers of velocities 1.86-2.51 km/set and 3.57-3.78 km/set are defined. Velocities of 4.36-4.82 km/set are derived for the Tertiary igneous rocks. Beneath the igneous sequence a two layer crust is observed, with the upper layer displaying velocities of 5.80-6.20 km/set and the lower layer 6.45-6.60 km/set. Moho velocities of 8.0-8.2 km/set are determined at a depth of 12.6 km beneath the Rockall Trough. Fiaytrace modelling by the Box method IS used to confirm the model and reveals a shallow, two-layer continental crust deepening to the east and west.