Crustal structure of the British Isles and its epeirogenic consequences

Abstract

S U M M A R YCrustal 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 V p /V s 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, wideangle 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.

Deep structure of the northern North Sea and southwestern Norway based on 3D density and magnetic modelling

“…During the last decade, several regional compilations of the Moho have been published by Ziegler & Dèzes (2006), Kelly et al (2007), Tesauro et al (2008), Grad et al (2009), Davis et al (2012), and . The major structural trend of the crust-mantle boundary is always consistent within the study area, demonstrating that the crust is thick beneath the Norwegian mainland and is relatively thin beneath the sedimentary basins within the central part of the North Sea.…”

Planation surfaces of the Armorican Massif (western France):Denudation chronology of a Mesozoic land surface twice exhumed in response to relative crustal movements between Iberia and Eurasia

“…Likewise, the British Isles basins were deformed (inversion) and exhumed (Holford et al, 2005;Hillis et al, 2008) during the early Cretaceous (St-Georges Channel and East Irish Sea Basins) and early Cenozoic (Wessex-Weald Basin, East Irish Sea). The cause of this deformation remains debated, being either due to uplift as a result of the relative movements between Africa, Iberia and Eurasia (Hillis et al, 2008), or to the Paleocene-Eocene Icelandic plume (Davis et al, 2012). In conclusion, the two periods of exhumation (early Cretaceous and earliest Cenozoic) are chiefly linked to the relative movements between Africa, Iberia and Eurasia, first under a regime of plate divergence, and subsequently under a regime of convergence.…”

Local earthquake tomography of Scotland

“…However, a few kilometres further along the profile the contour can be seen to be sloping upwards in a northerly direction at a depth of about 28km. (Tomlinson, 2006), (Di Leo et al, 2009) and (Davis et al, 2012) all used teleseismic P-wave receiver functions to determine variations in crustal thickness and Vp/Vs ratio across Scotland. These studies essentially agree with the LISPB results and show crustal thickness varying from about 23 km in the north-eastern highlands to more than 30 km near the Highland Boundary Fault.…”

“…The ratio used was found by making a compound Wadati plot of the entire data set. The value found was 1.72 with a standard deviation of 0.03, which falls within the ranges found using receiver functions by (Di Leo et al, 2009) and (Tomlinson, 2006) and is close to the 1.74 value found by (Davis et al, 2012). Station corrections were calculated relative to station ELO (Figure 2), a station in the centre of Scotland that was used in over half of the events.…”

“…(Hardwick, 2008) constructed 3-D seismic velocity models for England and Wales using local earthquake tomography that broadly agree with observed geology. (Asencio et al, 2003), (Tomlinson, 2006), (Di Leo et al, 2009) and (Davis et al, 2012) all use teleseismic receiver functions to identify various features of the crust and upper mantle under the UK, including the thickness of the crust. However, to date, there have been no published studies that have used local earthquake tomography to image the crust under the northern part of the British Isles.…”