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

SUMMARY 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.