Borehole records, seismic reflection traverses and surface resistivity surveys have established the presence of previously unknown graben complexes north of York. A major NE–SW to E–W trending complex with vertical displacements of up to around 200 m is traceable for 22 km through Beningbrough and Strensall. A narrower NW-SE trending graben with similar displacements can be traced for at least 8 km through Lilling, south of Sheriff Hutton. A large part of the Beningbrough-Strensall Graben Zone is complexly faulted on both large and small scales. It is located at the southern edge of the Howardian-Flambor-ough Head Fault Zone and may have been within an area of maximum ‘sag’ deformation along the hinge between the subsiding Cleveland Basin to the north and the more rigid Market Weighton Block to the south. Major consequences of the faulting are: (i) a 10 km sinistral shift of the sub-drift crop of the Triassic Mercia Mudstone Group, (ii) substantial changes to ground water levels and flow, and (iii) the presence of small fault bounded blocks of Rhaetian Penarth Group rocks many kilometres from their main sub-drift crop.

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