Dynamic Topology: A New Approach to Help Distinguish Modes of Rift Fault Network Formation?

Abstract

The evolution of rift fault networks is typically associated with changes in the size, density and throw characteristics of constituent faults. Many studies have statistically analysed such changes to determine how strain is accommodated across fault networks through time. Although useful, such analyses neglect to incorporate the arrangement of, and relationships between, faults in the network, that is, the network topology. As such, changes in fault intersection type and frequency that occur in evolving networks, aspects that become increasingly critical in networks with faults sets of different orientations, have not previously been explored. Analysis of fault network topology has previously been applied to final fault networks with the aim of understanding fault connectivity and fluid flow in a ‘static’ sense. These studies divide the network into nodes and branches. Nodes are classified as either intersections between faults or free fault tips, whereas branches represent portions of the faults in between nodes and are classified according to the degree of connectivity to other branches. The topology of a given network is determined by plotting the total number and ratio of different node or branch types on ternary plots. Here we build on this approach by introducing the concept of ‘dynamic’ topology, that is, quantifying changes in the topology of a given network through time. In particular, we assess if: i) ‘dynamic’ topology can elucidate trends as a given fault network evolves; and ii) rifts of different types (e.g. single phase rifts, multiphase rifts etc) have distinctive evolutionary pathways. To achieve these aims we constrain and compare topology data from sequential plan view fault maps from physical models of different rift types. Physical model outputs are ideal for this study as map view fault intersections are well imaged and boundary conditions controlling the formation of the fault networks are tightly-constrained. We then test the applicability of ‘dynamic’ topology to natural fault systems, applying the approach to seismically imaged natural fault networks. Our results indicate: (1) ‘dynamic’ topology can be applied to fault networks from rifts with different modes of formation; (2) as fault networks mature there are marked changes in intersection type and frequency, along with overall increases in fault connectivity that are captured in ternary plots; and, strikingly, (3)) rifts of different types have distinctive evolutionary pathways.

AAPG Datapages/Search and Discovery Article #90216 ©2015 AAPG Annual Convention and Exhibition, Denver, CO., May 31 - June 3, 2015