Abstract

The Central Electricity Generating Board are seeking licence and planning approval to build a Pressurized Water Reactor just to the west of the existing Advanced Gas-Cooled Reactor at Hinkley Point, Somerset. As part of a seismic hazard evaluation both regional and local geology have had to be studied in detail.

The site is located in a complex structural setting at the eastern end of the North Somerset coastal fault belt. Detailed field mapping was carried out on the foreshore from just east of Hinkley Point to just west of Watchet with the purpose of identifying structural style, sequence of faulting and approximate age of the last movement. When assessing the seismotectonics of the region it was necessary to study the degree of middle and late stage Tertiary inversion prominent in southern England, less evident in the immediate vicinity of Hinkley Point.

Of especial interest is the north-west-south-east trending Watchet-Cothelstone-Hatch Fault and its relationship to the east-west trending faults passing close to Hinkley Point.

The Watchet Fault truncates the main east-west trending faults in the foreshore inducing a marked drag towards the fault plane, thus this phase of movement on the north-west trending fault is younger than the generally vertical displacements associated with the east-west trending faults. Examination of gypsum slickensides shows that the influence of the later movement of the north-west trending fault on reactivation of the east-west trending faults, did not extend beyond 350 m east from the main fault plane.

The fault plane of the Watchet Fault is

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