ESSOAr | https:/doi.org/10.1002/essoar.10501104.1 | CC_BY_NC_ND_4.0 | First posted online: Mon, 11 Nov 2019 01:27:37 | This content has not been peer reviewed. Geometry of the Butterknowle Fault at Bishop Auckland (County Durham, UK), from gravity survey and structural inversion Rob Westaway 1,*, Sean M. Watson 1, Aaron Williams 1, Tom L. Harley 2, and Richard Middlemiss 3 1 James Watt School of Engineering, University of Glasgow, James Watt (South) Building, Glasgow G12 8QQ, UK. 2 WSP, 70 Chancery Lane, London WC2A 1AF, UK. 3 School of Physics, University of Glasgow, Kelvin Building, Glasgow G12 8QQ, UK. * Correspondence:
[email protected]; Abstract: The Butterknowle Fault is a major normal fault of Dinantian age in northern England, bounding the Stainmore Basin and the Alston Block. This fault zone has been proposed as a source of deep geothermal energy; to facilitate the design of a geothermal project in the town of Bishop Auckland further investigation of its geometry was necessary and led to the present study. We show using three-dimensional modelling of a dense local gravity survey, combined with structural inversion, that this fault has a ramp-flat-ramp geometry, ~250 m of latest Carboniferous / Early Permian downthrow having occurred on a fault surface that is not a planar updip continuation of that which had accommodated the many kilometres of Dinantian extension. The gravity survey also reveals relatively low-density sediments in the hanging-wall of the Dinantian fault, interpreted as porous alluvial fan deposits, indicating that a favourable geothermal target indeed exists in the area.