A relative P-wave delay study between Eskdalemuir and Charnwood Forest

Summary. The relative P-wave delay between CWF, a permanent seismic station on the Precambrian rocks of Charnwood Forest in the English Midlands and EKA, the Eskdalemuir Seismological Array, shows a large azimuthal variation of 1.3 s. This is examined and is consistent with a thinning of the crust from EKA to CWF, together with a considerable thickness of high velocity (most probably greater than 7.0 km s−1) lower crust beneath CWF. The Southern Uplands Fault, approximately 42 km to the north-west at its closest approach to EKA, seems to be associated with a large anomaly in the relative P-wave delay. Raypaths from events originating between azimuths 260 to 350° from EKA apparently pass through anomalously high velocity material entering the crust just to the south of the fault.