Physics
Scientific paper
Dec 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010agufm.t52a..06w&link_type=abstract
American Geophysical Union, Fall Meeting 2010, abstract #T52A-06
Physics
[5475] Planetary Sciences: Solid Surface Planets / Tectonics, [6225] Planetary Sciences: Solar System Objects / Mars, [8109] Tectonophysics / Continental Tectonics: Extensional
Scientific paper
Normal faults evolve from systems of unconnected fault ruptures, to poorly connected networks formed by linkage of propagating faults, to strongly interconnected fault networks with isolated fault blocks. This evolution tends to progress with increasing duration or magnitude of extension. Individual faults develop sawtooth along-strike displacement profiles, which are attributed to growth by fault linkage. The relationship between maximum displacement and tracelength (Dmax/L) of faults has been studied for at least two decades, in particular the extent to which this relationship represents self-similar fault development or not, and whether it represents some fundamental characteristic of the faulted medium, displacement accumulation, or fault linkage processes. There is, however, a distinction between displacement versus length relationships for individual faults, fault arrays consisting of multiple cooperating faults, and individual faults within a fault array, and there is a growing body of evidence that fault ruptures do not grow by self-similar increments, but evolve to higher maximum displacement to length ratios with successive slip events. Normal faults observed in extensional clay models evolve by displacement (throw) accumulation and concomitant trace length increase, and by segment linkage. The first of these processes leads to an increase in the maximum throw to trace length (Dmax/L) ratio, whereas the second leads to a decrease in this ratio. With increasing extension individual faults evolve along stepwise tracks in Dmax/L parameter space, although at any given time a summary plot of Dmax versus L for the entire fault population will typically span one order of magnitude in Dmax/L ratio and two orders of magnitude in trace length, obscuring the stepwise nature of fault evolution and giving the impression of self-similar fault growth along a locus of constant Dmax/L ratio. In addition, the number of simple faults (faults with a single throw maximum) incorporated into a compound fault (a fault with multiple throw maxima) is strongly correlated with the fault’s trace length, indicating that trace length increase is dominated by linkage not throw accumulation. Extensional faults in the northwest quadrant of Alba Patera, Mars, provide excellent analogs for fault development on Earth. When analyzed for evidence of relict simple faults (expressed as throw maxima), normal faults observed on Mars exhibit similar characteristics to those developed in analog clay models. The number of segments incorporated into compound faults is positively correlated with trace length, similar to modeling results. In addition, compound faults are distributed over two orders of magnitude in trace length and have Dmax/L ratios from 2 × 10-3 to 2 × 10-1. We interpret these observations to indicate that individual faults do not grow simply by self-similar increments. Individual segments grow primarily by throw accumulation rather than by increasing trace length, but at any stage in this process may become linked to other segments and then the whole fault will evolve to lower Dmax/L ratios as more segments are incorporated into it.
Ferrill David A.
Morris Alan P.
Wyrick Danielle Y.
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