Crustal structure of the British Isles and its epeirogenic consequences

Abstract

Crustal receiver functions have been calculated for a network of 51 three-component broadband seismometers distributed across the British Isles and NW Europe. Over 3200 receiver functions were assembled for 1055 events. For each station, preliminary estimates of crustal thickness and Vp/Vs ratio were obtained from H−κ plots. Stacked receiver functions were then inverted to determine shear wave velocity as a function of depth. Each result was checked by guided forward modelling and by Monte Carlo error analysis. In this way, the robustness of our final calculated velocity profiles was carefully tested. A set of depth migrated profiles was also constructed using an average of 50 events for each station over a range of backazimuths. These profiles agree well with legacy wide-angle crustal models. Our results show that crustal thickness varies between 24 and 36 km across the British Isles. Thicker crust is found beneath north Wales and beneath central Scotland. Thinner crust occurs beneath northwest Scotland and northwest Ireland. By combining our database with the results of controlled source, wide-angle experiments and with depth-converted reflection profiles, we have produced a detailed crustal thickness map for a region encompassing the British Isles. Our synthesis of crustal thickness and structure has important implications for the tectonic and magmatic histories of this region. Complex Moho structure with lower crustal P-wave velocities of >7 km s−1 occurs beneath regions of Cenozoic magmatism, which may be consistent with magmatic underplating. Thin crust beneath northern Britain suggests that present-day long wavelength topography is maintained by regional dynamic support, originating beneath the lithospheric plate.