Fault zone architecture of a large plate-bounding strike-slip fault: a case study from the Alpine Fault, New Zealand

Bernhard Schuck,Anja M. Schleicher,Virginia G. Toy,Christoph Janssen,Georg Dresen

doi:10.5194/se-11-95-2020

Abstract

Abstract. New Zealand's Alpine Fault is a large, plate-bounding strike-slip fault, which ruptures in large (Mw>8) earthquakes. We conducted field and laboratory analyses of fault rocks to assess its fault zone architecture. Results reveal that the Alpine Fault Zone has a complex geometry, comprising an anastomosing network of multiple slip planes that have accommodated different amounts of displacement. This contrasts with the previous perception of the Alpine Fault Zone, which assumes a single principal slip zone accommodated all displacement. This interpretation is supported by results of drilling projects and geophysical investigations. Furthermore, observations presented here show that the young, largely unconsolidated sediments that constitute the footwall at shallow depths have a significant influence on fault gouge rheological properties and structure.

Highlights

A fault, a planar discontinuity in rock where one side has moved relative to the other parallel to the discontinuity plane, constitutes a rheological and mechanical manifestation of localized deformation (Twiss and Moores, 2007; Ben-Zion, 2008; Fossen, 2016; Fossen and Cavalcante, 2017)
Isocon analyses clearly demonstrate that all investigated fault rocks have been substantially altered by fluids (Fig. 9; Table 6), which is shown by the presence of authigenic phyllosilicates (Fig. 6a and k) and calcite vein networks (Fig. 7j–m)
If we employ the simple relationship that shear strain in a fault zone is equal to zone width multiplied by boundary displacement, and assume constant strain distribution within the principal slip zones (PSZs) gouges, the PSZ thickness variations we describe suggest the studied fault gouges accommodated different amounts of coseismic displacement

Summary

Introduction

A fault, a planar discontinuity in rock where one side has moved relative to the other parallel to the discontinuity plane, constitutes a rheological and mechanical manifestation of localized deformation (Twiss and Moores, 2007; Ben-Zion, 2008; Fossen, 2016; Fossen and Cavalcante, 2017). The structure, composition, hydrological properties and seismo-mechanical behavior of faults are typically intimately related. These interactions govern strain distribution and depend on various factors, such as lithology (Faulkner et al, 2003; Schleicher et al, 2010; Holdsworth et al, 2011; Rybacki et al, 2011), fluid pressure (Hickman et al, 1995; Janssen et al, 1998; Fagereng et al, 2010), stress field and stress magnitudes (Sibson, 1985; Faulkner et al, 2006; Lindsey et al, 2014).

Methods

Results

Discussion

Conclusion