Moho depth and Vp/Vs in Ireland from teleseismic receiver functions analysis

Abstract

This work presents a teleseismic P-wave receiver function study on 34 stations deployed across Ireland in order to determine the first-order crustal properties, thickness (H) and mean crustal Vp/Vs, over the entire island. We apply the H - Vp/Vs stacking method, which exploits the information contained in both the Ps and the multiple phases from the free-surface. In this way, we obtain the first Moho depth and Vp/Vs maps of Ireland based on a uniform distribution of measurements. The results are used to examine in detail the lateral variation of crustal thickness and Vp/Vs ratio across the major terrane boundaries in Ireland. Our results show a good agreement with the available previous estimates from onshore wide-angle/refraction experiments and add new information in poorly constrained areas such as Northern Ireland and the NW coast of Ireland. The mean Vp/Vs ratio is 1.73 ± 0.05 with a consistently low (≈1.70) value in the Leinster domain and in central Ireland. The mean crustal thickness is 30.9 ± 2.3 km. The southern portion of the island shows a nearly flat Moho at a depth of 32-33 km, while north of the Southern Uplands Fault, a relatively higher spatial frequency variation in Moho topography exists with values ranging from 28 to 32 km. This reflects the complex history of multiphase terranes accretion during the Caledonian orogeny, although locally, the superposition of more recent geological processes is not excluded. Crossing the Iapetus Suture Zone, our results support the presence of a 'transitional' Moho, that is, a 3-4 km smooth seismic transition between crust and mantle, while Moho depth remains constant. Anomalous values in Northern Ireland are interpreted as evidence of a 5- to 6-km-thick high S-wave velocity layer just above the Moho. © The Authors 2014. Published by Oxford University Press on behalf of the Royal Astronomical Society.