Abstract - Coal mineplan data from the Carboniferous East Pennine Coalfield (EPC) have been used to construct a high quality 1000km2 fault map which permits examination of a broader range of fault scaling properties than is generally possible. The fault map contains over 8000 faults, with throws in the range of 200m down to < 1m, and a lateral resolution of ca 10m. The faults are late Carboniferous post-depositional normal faults that form an orthogonal fault network of NW- and NE-striking faults: syn-depositional normal faults and post-depositional strike-slip faults occasionally occur but are of minor significance. The Coal Measure sequence overlies Dinantian extensional basins, from which it inherited important elements of its structure.
Maximum throw and length populations for each fault set and for the entire fault system define power-law distributions. Fault length populations, the most commonly used measure of fault size, are shown to be very sensitive to resolution effects, and will generally provide apparently non-power law distributions, even for systems with power-law scaling properties. Similarly, the exponent describing the relationship between fault length and maximum displacement, which for this dataset is greater than ca 1.3, will generally be lower, and approaching 1, for lower quality datasets.
The spatial characteristics of the system have been analysed using a range of fractal methods, none of which are capable of discriminating adequately between the EPC fault system and a similar synthetic fault system that possess random spatial properties. Instead, we use other measures of spatial properties, which show that the EPC fault system is better connected, more clustered and shows more heterogeneous strain distributions than an equivalent synthetic fault system. Strain is localised onto more discrete, laterally continuous faults within the EPC fault system and there is an increase in the degree of strain localisation at increasingly larger scales. Spatial fault density and strain do not, therefore, correlate well, with NW-striking faults localising more displacement and strain, but without higher fault densities, than NE-striking faults. These features collectively suggest that fault clustering, and damage zones, are a feature of the early localisation of faults, and that the subsequent generation of new faults adjacent to larger faults is less common.
Abstract of talk given to:
Tectonic Studies Group Annual Meeting, Tectonic Studies Group, University of Leeds, January 2001