HR: 1330h
AN: T22B-0510    [PDF]
TI: Effects of Young's Modulus on Fault-Zone Development and Displacements
AU: * Gudmundsson, A
EM: Agust.Gudmundsson@gwdg.de
AF: Department of Structural Geology and Geodynamics, University of Gottingen, Goldschmidtstrasse 3, Gottingen, D-37077 Germany
AB: Many fault populations, particularly those formed in a single tectonic environment where the host rocks have similar mechanical properties, display a roughly linear relationship between fault rupture (trace) length (L) and the maximum vertical displacement (u). However, the linear relationships vary; not only between fault populations, but also within a population, and on individual faults as well. Thus, although roughly linear relations commonly exist for individual faults over short periods of time, over longer periods of time the correlation between rupture length and displacement has a large scatter, commonly by an order of a magnitude or more. These observations suggest that some properties of the rock determining the fault displacement may by highly variable. Field observations show that fault zones normally consist of two main structural units: a fault core and a fault damage zone. In major fault zones, the core is from several meters to tens of meters thick and contains many small faults and fractures. Its most distinctive features, however, are breccias and other cataclastic rocks. The fault damage zone, which in major fault zones may be as thick as several kilometers, consists primarily of numerous fractures and faults that commonly increase gradually in number toward the core. As the core and the damage zone change with time, so do their mechanical properties, in particular the Young's modulus (stiffness). Elastic crack models predict a linear relationship between displacement (u) and rupture length (L) during slip in a fault zone. Attempts to find universal scaling laws for L/u, however, have generally failed; partly, I suggest, because they do not take into account the changes in the mechanical properties of the fault zone as it evolves. I propose that Young's modulus affects fault displacement both spatially and temporally: spatially when the trace of a fault at a given time dissects host rocks of different stiffnesses, and temporally when the stiffness of the fault zone itself changes. During the evolution of an active fault zone, the stiffness of its damage zone and fault core normally decreases, and so does the L/u ratio of the fault. By contrast, during inactive periods sealing and healing of the damage zone and core may increase the stiffness, hence the L/u ratio in subsequent slips. This model predicts that not only will the scaling of L/u within a given fault population vary in space and time, but also that of individual faults. This model may, partly at least, explain the large temporal and spatial variation in length/displacement ratios of faults.
DE: 8010 Fractures and faults
DE: 8020 Mechanics
DE: 8120 Dynamics of lithosphere and mantle--general
DE: 8123 Dynamics, seismotectonics
SC: Tectonophysics [T]
MN: 2003 Fall Meeting