Strong, wide-angle reflection events were detected during a crustal seismic experiment carried out in SW Britain in 1979. Three crustal reflectors have been identified, referred to as Rl, R2 and R3. Rl lies at a depth of about 8 km and appears to be restricted to the interior of the granite batholith underlying SW England. The nature of this reflector is unknown. R2 is a mid-crustal reflector lying at a depth of 10–15 km and interpreted as rising gradually northwards. It coincides locally with the base of the granite as predicted by gravity modeling, but extends well beyond the northern limit of the granite body. It is suggested that R2 may represent a major thrust of late Variscan age. R3 is the deepest reflector identified and lies at a depth of 27–30 km. R3 is interpreted as the base of the crust and its computed depth is in close agreement with the local depth to the Moho derived from an earlier seismic experiment in SW Britain.

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