Fault Linkage Styles in Rifts: Observations From Northern North Sea Rift Basin

Abstract

Normal fault systems and fault population are the result of an evolutionary process from nucleation to the development of large and sometimes complicated fault arrays, an evolution that in most cases involves various types of fault interaction. During the process of fault growth, tips of individual faults interact as their strain fields overlap, which may lead to a history of fault linkage through the formation and eventually destruction (breaching) of relay structures. On the geologic timescale, fault linkage structures are transient elements of a normal fault population, implying variations in their spatial and temporal distribution according to the level of structural observation. It implies a complex segmented three-dimensional fault geometry. The present study is based on 2D and 3D seismic interpretation to analyse the fault linkage styles along individual fault systems and across fault arrays in northern North Sea rift system. The observations are consistent with other's observations that, fault linkage represents a fundamental role in the formation of large fault systems. This is observed by the along-strike throw distribution in the master faults, where many throw minima are observed. These points of throw minima, which are not related to fault-propagation folding, are interpreted as linkage points. The relay ramps, which represent the main expressions of interaction and linkage, are not often seen along the master faults due the high displacements rates acquired after linkage, which implied the relay ramps destruction. In addition, the points of throw minima match regions of marked changes in fault strike. Where relay ramps are preserved, many features are observed. Scaling parameters may, or may not characterize an end-member type. The relationship between offset and fault overlap does not characterize an end-member type. All the relay ramp types may occur in any separation-overlap ratio from two to four. However, the curvature of unbreached relay ramps represents the lower values of mean dip, while breached examples show the higher values. In addition, the mean dip values of breached ramps show a bimodal distribution of low and high values. One explanation is, if the development of secondary failure across the relay ramp occurs early in the fault sequence, the rotated area may show little differential rotation, whereas at a late stage the breached area may retain the high original curvature of the original relay ramp

AAPG Datapages/Search and Discovery Article #90217 © 2015 International Conference & Exhibition, Melbourne, Australia, September 13-16, 2015