Vibroseis seismic data were acquired by Goal Petroleum plc during 1982 in the vicinity of the Somerton Anticline, Somerset. These data show the simple form of the anticline but in addition show a southward-dipping, discontinuous seismic event beneath. Gravity modelling demonstrates that this event may be correlated with an E–W-trending gravity gradient which can be followed for approximately 150 km. The dipping seismic event may represent a Variscan thrust plane which dips to the SSW in contrast to similar planes seen to the east which dip to the SSE. The variation in dip seen between these postulated thrust planes may explain the curvature of structural trends seen within, and to the east of, the Mendip Hills. The Polden Hills Fault runs sub-parallel to the proposed thrust plane beneath the Somerton Anticline and may be linked to a Mesozoic reactivation of the postulated thrust.