Distributed and localized faulting in extensional settings: Insight from the North Ethiopian Rift–Afar transition area

Abstract

[1] Extensional fault systems in the Earth's crust can exhibit two end-member geometries that we identify as distributed and localized faulting regimes. A satellite image analysis of fault populations from the Main Ethiopian Rift-Afar area reveals that the rift architecture contains these two faulting regimes. The occurrence of these regimes reveals a jump in the scale of fault segmentation and linkage. Strain localization at rift border zones exhibits particularly large-scale fault linkage and a power law size distribution. This regime replaces prior distributed fault systems, showing smallscale fault linkage and an exponential size distribution. The distributed faulting is interpreted as confined to the thick trap basalt carapace. We show that continental fault systems can develop by a combination of these two geometries, and we demonstrate how to quantitatively decipher the jump between them. Citation: Soliva, R., and R. A. Schultz (2008), Distributed and localized faulting in extensional settings:

The Ethiopia Afar Geoscientific Lithospheric Experiment (EAGLE): Probing the transition from continental rifting to incipient seafloor spreading

“…This lends some support to the importance of aseismic processes (e.g., diking) in accommodating strain (Hofstetter and Beyth, 2003). Localized, rift-axial brittle failure in the Main Ethiopian Rift is manifest in development of extensional fi ssures at the surface and associated fault growth in the upper crust (e.g., Asfaw, 1982;Acocella and Korme, 2002;Acocella et al, 2003;Williams et al, 2004;Soliva and Schultz, 2008;Kidane et al, 2009). In addition to brittle strain, magma intrusion and extrusion processes in the Main Ethiopian Rift are known to have occurred episodically since historical times to the present day (e.g., Gibson, 1969;Tadesse et al, 2003;Williams et al, 2004).…”

Scaling of fault attributes: A review

“…(1)) is best suited for describing the distribution of fault attributes, where attribute is expressed either as displacement or dimension, although other types of distributions such as exponential have been previously addressed (see e.g. Cowie et al, 1994;Ackermann et al, 2001;Soliva and Schultz, 2008).…”

Interpretation and analysis of planetary structures

“…Faults that affect vertically unconfined rock volumes (thick-skinned tectonics) exhibit a power-law behavior, reflecting the self-similar geometry of faults (with linear displacement-length scaling; Schultz and Fossen, 2002;Soliva et al, 2005). On the other hand, the displacement-length relationship of faults affecting a brittle rock layer with a limited thickness is scaledependent, and can be fitted with exponential functions (Soliva and Schultz, 2008).…”

“…Statistical analysis of fault populations can provide insight into the mechanical properties of the faulted volume, i.e., about the different mechanical properties of layers in a stratigraphic sequence (e.g., Soliva and Schultz, 2008;Polit et al, 2009). Histograms of cumulative frequency of fault length distributions may be approximated by power-law or exponential functions (e.g., Ackermann et al, 2001).…”

“…Best fits are shown for power-law and exponential functions (fit functions labeled on graph). A length truncation limit (lower bias) of 2 km was applied, following the considerations of Soliva and Schultz (2008) and applying them to the HRSC data set with a mapprojected image resolution of 25 m/pixel. No censoring effect (upper bias) was considered, since the mapping window was large with respect to the mapped grabens.…”