Scaling of fault displacements from the Badajoz-Cordoba shear zone, SW Spain


Jackson, Paul and Sanderson, David J. (1992) Scaling of fault displacements from the Badajoz-Cordoba shear zone, SW Spain. Tectonophysics, 210, (3-4), 179-190. (doi:10.1016/0040-1951(92)90321-V).

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Description/Abstract

Faulting occurs over a large range of scale, parts of which are sampled by various techniques (e.g., microscopy, outcrop measurement, mapping, seismic reflection and other forms of remote sensing). Use of a single technique to measure displacement or strain will not sample faults at all scales and hence will give a biased estimate. In order to assess this bias, a knowledge of the distribution over all scales is needed.

Many samples of fault displacement appear to follow a power-law distribution, with departures which can be attributed to sampling effects. The number of faults with a displacement u is given by N(u) = Cu−D. The power-law distribution of displacement is consistent with similar distributions of other fault parameters and earthquake magnitudes. When sampling along a line (e.g., a bedding trace on a map or section), a self-similar fault population would have D = 1, whereas self-affine geometries yield D≠ 1. Displacement and extension are dominated by small faults when D > 1 and by large faults when D < 1. When sampling over areas or volumes these critical values are 2 and 3, respectively.

A set of strike-slip faults from the Badajoz-Córdoba Shear Zone, Spain, were sampled at two different scales using 1:50000 maps and outcrop measurements. Displacement ranges over 6 orders of magnitude. These and other fault populations typically have D ranging from 0.6 to 1.5.

The power-law relationship may be integrated to yield estimates of the displacement (or extension) for faults which lie beyond the resolution of the sampling system. For example, a knowledge of D allows the extension measured on a map or seismic section to be “corrected” for faults whose displacement is below the resolution of the survey. Based on an overall estimate of D = 0.9 for the Badajoz-Córdoba data, only some 40% of the extension would be recorded by map-scale faults. A corrected extension of 41% along the shear zone is estimated; which if typical for the entire 300 km zone represents some 87 km of along-strike extension. Thus, work suggests that significant displacement occurs on faults which are too small to be interpreted from conventional seismic profiles and geological maps.

Item Type: Article
ISSNs: 0040-1951 (print)
Subjects: T Technology > TA Engineering (General). Civil engineering (General)
Q Science > QC Physics
Q Science > QE Geology
Divisions: University Structure - Pre August 2011 > School of Civil Engineering and the Environment
ePrint ID: 76044
Date Deposited: 11 Mar 2010
Last Modified: 27 Mar 2014 18:55
URI: http://eprints.soton.ac.uk/id/eprint/76044

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