Evolution of pull‐apart basins and their scale independence

Abstract

Pull‐apart basins or rhomb grabens and horsts along major strike‐slip fault systems in the world are generally associated with horizontal slip along faults. A simple model suggests that the width of the rhombs is controlled by the initial fault geometry, whereas the length increases with increasing fault displacement. We have tested this model by analyzing the shapes of 70 well‐defined rhomb‐like pull‐apart basins and pressure ridges, ranging from tens of meters to tens of kilometers in length, associated with several major strike‐slip faults in the western United States, Israel, Turkey, Iran, Guatemala, Venezuela, and New Zealand. In conflict with the model, we find that the length to width ratio of these basins is a constant value of approximately 3; these basins become wider as they grow longer with increasing fault offset. Two possible mechanisms responsible for the increase in width are suggested: (1) coalescence of neighboring rhomb grabens as each graben increases its length and (2) formation of fault strands parallel to the existing ones when large displacements need to be accommodated. The processes of formation and growth of new fault strands promote interaction among the new faults and between the new and preexisting faults on a larger scale. Increased displacement causes the width of the fault zone to increase resulting in wider pull‐apart basins.

Analysis of the growth of strike-slip faults using effective medium theory

“…1a). This discontinuous characteristic of strike-slip faults has been reported for simple incipient faults (Segal and Pollard, 1980;1983;Gamond, 1983;Willemse et al, 1987;Peacock and Sanderson, 1995) as well as for mature crustal scale faults (Aydin and Nur, 1982;Barka and Kadinsky-Cade, 1988;Wesnousky, 1988;Stirling et al, 1996, Kim et al, 2004 and is thought to be pertinent to a number of properties of strike-slip fault systems including their permeability structure (Sibson, 1985;Martel and Peterson, 1991;Aydin, 2000;Odling et al, 2004), the dynamics and size of earthquake ruptures (Aki, 1989;Wesnousky, 2006;Shaw and Dieterich, 2007), the spatial and temporal evolution of earthquakes (Dewey, 1976;Toksöz et al, 1979;Stein et al, 1997), and growth and scaling of faults (de Joussineau and Aydin, 2009;Scholz, 2002).…”

“…1a). It turns out that strike-slip steps have self similar geometry regardless of the sense of stepping and sense of shearing (Aydin and Schultz, 1990;Aydin and Nur, 1982). However, the failure modes and the distribution of the shearing-related structures may be different from one sense of step to another depending on loading, stress perturbations, rhelogy, and the geometry of initial pre-faulting discontinuities (Kim et al, 2004;Myers and Aydin 2004;Peacock and Sanderson, 1991;Burgmann and Pollard, 1994;Gamond, 1983;1987;Rispoli, 1981).…”

“…Although it is difficult to define uncertainty regarding the fault dimensions measured from published geologic and seismologic maps, recent experimental (Otsuki and Dilov, 2005) and site-specific field data from the same tectonic region and lithology and similar resolution (de Joussineau and Aydin, 2009) appear to confirm this trend. It is also interesting to note that larger size of steps is associated with faults having larger maximum slip magnitudes (Aydin and Nur, 1982;). …”

Heat flow in southernmost California and the origin of the Salton Trough

“…The model should also specify the size and shape of the deforming regio n in s uch a way that it can be shown realistically o n the geologic map. Several comprehensive discussio ns of pull-a part structures have been published [e.g., Crowell, 1914b;Mann eta/., 1983;Garfunkel, 1972a, b;Aydin and Nur, 1982], but we shall need to consider only two idealized extremes: one in which the extending region is small relative to crustal thickness ( Figure lib for simplicity, may be replaced by smooth ones (e.g., dashed, Figure lib) thereby permitting both the longterm simple shear and extension to be continuous throughout the basin. A smooth approach of long-term shear strain to discontinuous strike-slip displacement on the faults at P and Q would imply tangency of the basin boundary with the master faults there, thereby suggesting the sigmoidal boundary form shown (see also Mann et a/.…”

Evaluation of the seismicity of the southern Great Basin and its relationship to the tectonic framework of the region

“…In other concepts it is assumed that wrench, detachment, normal and thrust faulting occur contemporaneously and are different manifestations of the same deformational processes (Anderson, 1971;Wernicke, 1984;King, 1983;Aydin and Nur, 1982). Aydin and Nur (1982) suggest that transcurrent faulting is the principal mode of intraplate deformation and offsets in these transcurrent faults lead to secondary features such as basin and ridge formation. The basin formations have been termed pull-apart basins.…”