Analysis of a strike-slip fault network using high resolution multibeam bathymetry, offshore NW Devon U.K.

Abstract

Imaging of the sea floor offshore from Hartland Point (north Devon, U.K.), using high resolution multibeam bathymetry, reveals a strike-slip fault network. This consists of NE-trending left-lateral faults and NW-trending right-lateral faults that cut folded and steeply dipping strata (~ 60°). Faults were accurately mapped using the multibeam imagery, and lateral separations of marker beds measured along fault traces. These data are used to examine the spatial arrangement, fault displacement, and strain distribution within the network at different displacement cut-offs.

At high displacement cut-offs, the fault network is dominated by a few long isolated right-lateral fault segments that bound fault blocks, but at lower displacement cut-offs shorter left-lateral and right-lateral fault segments make up fault tips and infill fault blocks. The majority (70%) of fault trace-length is taken up by small fault segments that have < 10 m displacement whereas 84% of strain is localized onto large fault segments with > 10 m displacement. The topology and relative connectivity of the network is analysed in terms of a system of fault branches between tips (I-nodes) or intersections (X or Y-nodes), the relative proportions of which reflect the connectivity of the network. Although the kinematic behaviour of the fault network is controlled by large fault segments, connectivity is very dependent on the small fault segments.

A comparison with a similar, nearby, strike-slip fault network at Westward Ho! (north Devon) shows many similarities and indicates that fault networks are better connected with increasing strain and that the network becomes better connected when strain is localized within damage zones rather than on individual faults.

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Identifiers

ORCID for David J. Sanderson: orcid.org/0000-0002-2144-3527

ORCID for Jonathan M. Bull: orcid.org/0000-0003-3373-5807

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