Thrust-fault growth and segment linkage in the active Ostler fault zone, New Zealand
Introduction
The development of fault zones is a fundamental process in tectonics, with implications ranging from interpretation of seismic data to estimating brittle strain (Scholz, 1990). Nevertheless, the ways in which faults rupture, grow, and link remain poorly resolved. Extensive datasets from normal fault systems (Dawers and Anders, 1995, Manighetti et al., 2001, Walsh et al., 2003) have been used to examine fault populations with a large range in scale and relatively uniform tectonic and lithologic boundary conditions, thereby providing reliable tests of fault-growth models and fault-scaling laws for normal faults. Some of the more detailed studies consider systems of faults that are very well exposed, but are only a few meters in length (Soliva and Benedicto, 2004). At the scale of small outcrops, fully three-dimensional exposures can permit reliable documentation of distributed displacement within isolated, linked, and breached faults and ramps. Few temporal data are commonly available with such studies, and the reliability of extrapolating from metric scales to the larger spatial arrays of faults is usually unknown.
Few studies, moreover, investigate the detailed character of thrust-fault populations or their along-strike fault-displacement patterns. Most studies utilize cross-sections through ancient thrust faults, and their ability to resolve along-strike variations in displacement is limited as hanging wall cutoffs are commonly eroded and only exposed near the fault terminations (e.g. Elliott, 1976). Due to scarce data, key questions about thrust-fault growth and scaling remain unresolved. (1) How does displacement vary along the strike of a thrust fault? (2) How is displacement distributed and transferred among multiple segments (Fig. 1) within a fault zone? (3) How much strain occurs in the hanging walls of thrust faults, and how does this strain vary along strike? (4) What are the scaling laws for lengths and displacements of thrust fault segments? (5) What is the length–displacement relationship and displacement profile for active fault segments over thousands of years, and how do these datasets compare with the length–displacement relationship of a kinematically linked fault system in the long term?
In this paper, we characterize the geometry and scaling of fault segment length and displacement in an active, segmented thrust fault zone in New Zealand (Fig. 2), and we evaluate these results in the context of fault-growth and fault-segmentation models. Excellent exposure of the surface fault trace, as it disrupts a regionally extensive geomorphic marker surface, allows detailed along-strike displacement profiles to be constructed (Fig. 2c). We focus on two zones of thrust-fault linkage to illustrate how displacement is transferred across the zones and determine the effects of segment interaction on the fault-displacement profiles. Finally, we calculate scaling relationships for both the fault segment-size distribution and Dmax versus L for fault segments.
Section snippets
Fault scaling
Displacement profiles along faults can provide insight into fault-growth history and the effects of fault interaction (Peacock and Sanderson, 1991, Dawers and Anders, 1995, Gupta and Scholz, 1998, Gupta and Scholz, 2000, Manighetti et al., 2001). For some fault systems, characteristics such as fault-zone width, length, and displacement appear to obey simple scaling relationships as illustrated by global datasets of fault length (L) and maximum fault displacement (Dmax), primarily from normal
Study area
The Ostler fault zone (OFZ) is located in the intermontane Mackenzie Basin on the east flank of the Southern Alps, New Zealand (Fig. 2). Of the ∼40 mm/yr of oblique convergence between the Pacific and Australian plates, most deformation is accommodated by the Alpine Fault, west of the Southern Alps (Walcott, 1998, Tippett and Hovius, 2000, Norris and Cooper, 2001). Approximately one-third of the predicted relative plate motion occurring on the South Island is partitioned into structures east of
Methods
Forty fault scarps were surveyed using a Trimble 4700 differential GPS with centimeter-scale vertical and horizontal precision. Simultaneous tandem surveys along the top and base of each scarp provided horizontal and vertical coordinates every 1–3 m that were, in turn, used to generate detailed scarp height versus length plots (Fig. 3, Fig. 4). Scarp height is used as a proxy for fault displacement (as opposed to vertical throw) following two corrections. First, the slope of the offset
Displacement profiles and transfer zones
Along-strike displacement profiles were surveyed on ∼40 fault segments within the OFZ. Individual profiles all increase to a maximum displacement (Dmax) somewhere within the fault trace and decrease to measurable displacements of near zero at the tips (Fig. 4a), except for one-tip faults where length is extrapolated from the displacement profile (Fig. 4b). Beyond these general characteristics, displacement profiles show a wide variety of shapes from quasi-elliptical to triangular to box-shaped.
Sources of uncertainly in the dataset
As in most other Dmax–L datasets (Cowie and Scholz, 1992b, Gillespie et al., 1992, Schlische et al., 1996), data from the OFZ exhibit considerable scatter. In some cases, for a similar L, the Dmax can vary by a factor of 2 or 3. Variability in the data results from both measurement uncertainty and natural scatter. Monte Carlo simulations indicate that poorly constrained fault dip contributes most (∼40%) to the Dmax measurement error. Uncertainty in the dip of displaced geomorphic surfaces
Summary and conclusions
Displacement and length of ∼40 segments of the OFZ, New Zealand, were measured and analyzed in the first systematic study of along-strike displacement on mesoscale thrust faults. Deformation in this segmented, east-vergent fault zone is expressed as fault scarps and folds on a pristine ∼20 ka glacial outwash surface, as well as older, dissected and uplifted surfaces on the hanging wall. Our data and analyses support the following conclusions:
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Fault-displacement profiles display elliptical,
Acknowledgements
Haikai Tane of the Center for Catchment Ecology in Twizel, NZ provided assistance in the field, and high-resolution topographic data and aerial photography. The TOPSAR DEM used in this study was kindly supplied by NASA. This research was funded by National Science Foundation grant EAR-0117242. The manuscript was substantially improved by the incisive reviews of N. Dawers and A. Nicol.
References (54)
- et al.
Deformation monitoring of the Ostler fault zone, South Island, New Zealand
Tectonophysics
(1989) - et al.
Fault growth by segment linkage; an explanation for scatter in maximum displacement and trace length data from the Canyonlands Grabens of SE Utah
Journal of Structural Geology
(1995) - et al.
Are fault growth and linkage models consistent with power-law distributions of fault lengths
Journal of Structural Geology
(1996) - et al.
A modern regression approach to determining fault displacement–length scaling relationships
Journal of Structural Geology
(1996) - et al.
Physical explanation for the displacement–length relationship of faults using a post-yield fracture mechanics model
Journal of Structural Geology
(1992) - et al.
Displacement–length scaling relationship for faults: data synthesis and discussion
Journal of Structural Geology
(1992) - et al.
Quasistatic fault slip as an explanation for finite displacement gradients at fault tips
Journal of Structural Geology
(1998) - et al.
Displacement–length scaling and fault linkage
Journal of Structural Geology
(1995) - et al.
Limitations of dimension and displacement data from single faults and the consequences for data analysis and interpretation
Journal of Structural Geology
(1992) - et al.
A model of normal fault interaction based on observations and theory
Journal of Structural Geology
(2000)
Discontinuous fault zones
Journal of Structural Geology
Fault growth by linkage: observations and implications from analogue models
Journal of Structural Geology
Fault size distributions; are they really power-law?
Journal of Structural Geology
The shapes, major axis orientations and displacement patterns of fault surfaces
Journal of Structural Geology
Relay zones between mesoscopic thrust faults in layered sedimentary sequences
Journal of Structural Geology
Late Quaternary slip rates and slip partitioning on the Alpine Fault, New Zealand
Journal of Structural Geology
Displacement, segment linkage and relay ramps in normal fault zones
Journal of Structural Geology
Effects of propagation rate on displacement variations along faults
Journal of Geophysical Research
Theoretical displacements and stresses near fractures in rock; with applications to faults, joints, veins, dikes, and solution surfaces
Scaling properties of normal fault populations in the western Corinth Graben, Greece: implications for fault growth in large strain settings
Journal of Structural Geology
A linkage criterion for segmented normal faults
Journal of Structural Geology
Analysis of the relationship between displacements and dimensions of faults
Journal of Structural Geology
An alternative model for the growth of faults
Journal of Structural Geology
Strain localisation and population changes during fault system growth within the Inner Moray Firth, Northern North Sea
Journal of Structural Geology
Scaling systematics of fault sizes on a large-scale range fault map
Journal of Structural Geology
Fault displacement-gradient folds and the structure at Lost Hills, California
Journal of Structural Geology
3D analyses of slip distributions on normal fault arrays with consequences for fault scaling
Journal of Structural Geology
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Present address: Tonkin and Taylor, PO Box 1009, Nelson, New Zealand.