The 3D structure of a normal fault from multiple outcrop observations

Abstract

Extensive opencast lignite mining in the Ptolemais Basin, NW Greece has exposed a plethora of outcrops within a normal fault system offsetting a sequence of interbedded lignites and marls of Pliocene age. The entire length of a 630 m long fault over a vertical interval of 80 m has been mapped in detail from 48 mine faces. The mapped fault comprises 5 fault segments large enough to be mapped in 3D, smaller fault segments exposed on individual mine faces and associated continuous deformation in the form of bed rotations and normal drag. These fault components combined to provide a regular aggregate throw distribution over the mapped fault. The boundaries between adjacent fault segments have a variety of geometries and they may be fully unconnected or they may link along strike or down dip within the fault zone. The fault geometry and throw distribution is analysed using two approaches, a discrete mapping of the large fault segments and a continuous approach based on measures of fault thickness and throw partitioning at individual outcrops. This combination of approaches demonstrates that fault thickness and the proportion of fault throw on the individual fault segments observed on any cross-section through the fault are related almost entirely to fault segmentation in 3D.