VARNET-96: three-dimensional upper crustal velocity structure of SW Ireland

Abstract

During the VARNET-96 seismic experiment three seismic refraction/wide-angle reflection profiles were acquired in order to examine the crustal structure in the southwest of Ireland. A total of 170 seismic stations were used on 300 recording sites. The shotpoint geometry was designed to allow for inline and offline fan shot recordings on the three profiles, using a total of 34 shots. Results from 3-D ray-trace and inversion modelling illustrate the pervasive lateral heterogeneity of the crust south of the Shannon Estuary. About 5 km of interpreted Palaeozoic sediment at the south coast was associated with the sedimentary infill of the Munster and South Munster Basins. This sedimentary layer, which thins to approximately 2 km in the northern Munster Basin, is significantly thinner than previously estimated from geological field studies. High-velocity zones beneath Dingle Bay and the Kenmare River region may be associated with the deep traces of the Killarney-Mallow Fault Zone and the Cork-Kenmare line. A zone of high-velocity upper crust (6.4-6.6 km s - 1 ) beneath the South Munster Basin is found in the area between the Kenmare-Killarney and the Leinster Granite gravity lows. The depth to the Moho varies from approximately 28-29 km at the south coast to approximately 32-33 km in the Dingle-Shannon Basin. The interpretation of the 2-D and 3-D velocity models suggests that Variscan deformation is confined to sedimentary and upper crustal structures in the southwest of Ireland.