Geomorphology of kilometer-scale extensional fault scarps: factors that impact seismic interpretation

Abstract

The geometry of kilometer-scale extensional fault scarps appears to generally result from the interaction of three factors: initial tectonic style of the fault block, mass wasting, and setting (subareal vs. submarine). These factors are drawn together here in a matrix-style framework that highlights their interrelationships, having the intent of facilitating timely recognition of geophysical artifacts and alternative geological models during seismic interpretation. A brief review of these factors and how they could interact to affect seismic-scale fault block geometry make up this framework. This conceptual framework is then applied to a case study of seismic examples of fault blocks from the Jurassic North Sea rift. These examples span several settings from subareal to submarine exposure, with a variety of footwall lithologies. The results show that scarps that stood in deep water for as much as 50 m.y. were relatively unaffected by mass wasting, although the scarps exposed a wide variety of lithologies and structures. The principal influence on their final morphology was initial fault plane shape. However, subareally exposed scarps were strongly degraded, showing that degradation models for subareal scarps do not apply to submarine scarps. We also found that kilometer-scale posttectonic gravity collapse blocks are relatively uncommon in the study area, but where present, they can be misinterpreted as strike-slip fault zones.