The morphological characteristics of normal fault traces in the Apennines, Italy

Abstract

Fault trace ruptures at the Earth’s surface show sinuosity (departure from linear trace morphologies) at a variety of scales in map view, reflecting the growth of the fault, the mechanical stratigraphy of the surrounding geology, and interactions with neighbouring faults. This study uses a combination of new remotely sensed LiDAR and SRTM datasets, and novel techniques which seek to eliminate the distorting effects of topography upon the fault traces.
The 2D morphological characteristics of fault traces are mapped and quantified. The relationships between those characteristics and scale of observation and other fault parameters are investigated, to see what insight those relationships afford into fault growth and interaction. By characterising controls of sinuosity at different scales, a better understanding of the effect of fault trace variations on seismic hazard evaluation in active tectonic regions may be obtained.
At the whole fault scale, stress interactions between neighbouring faults and between en échelon segments within a fault appear to be the main controls on trace sinuosity. Linear correlations between sinuosity values and fault length and slip rate respectively are weak. However, sinuosity appears to be smoothed out with repeated slip, particularly in central parts of the fault traces.
At smaller scale (<100 m), sinuosity is more variable and values spread over a wider range. Local features such as pre-existing fractures/weaknesses appear to be a principal control over deviation. Sinuosity is apparently not much influenced by the controlling factors at the whole fault scale.
The current regional extensional stress regime sees normal faults striking broadly SE-NW. Deviation from that pattern may be a significant factor in controlling sinuosity at the whole fault level. Here, anticlockwise deviance from the regional strike appears to coincide with an increase in sinuosity values. The anticlockwise variance brings the faults closer to a previous extensional regime, which left inherited structures trending broadly SW-NE. Those minor structures could be reactivated as transfer faults or segments between en échelon faults or fault segments, particularly in left-stepping situations.