The earliest ideas about continental drift (Wegener 1929) were based on the observation that the eastern coasts of North and South America matched the shape of the western coasts of Europe and Africa. This implies that the continents somehow split apart. Plate tectonics holds that continental breakup involves rifting the entire lithosphere, the cold outer layer of the earth that is too strong to flow along with the deeper interior.

During the thirty plus years since the acceptance of plate tectonics, much effort has been made to characterize rifts and rifted margins and understand the processes affecting them. One of...

The simple concepts of plate tectonics, in which the deformation of the ocean basins is adequately described by the relative motions of rigid blocks, are not easily applicable in continental tectonics, where the deformation is usually much more diffuse than in the oceans and is not restricted to narrow plate boundaries (McKenzie 1972; Molnar and Tapponnier 1975). A different framework is therefore needed within which to view continental deformation. Within the broad deforming belts on the continents some large, flat, aseismic regions such as central Turkey, central Iran, and the Tarim basin appear to be rigid and can usefully be...

Since their discovery in the Basin and Range province (Longwell 1945; Anderson 1971; Armstrong 1972; Crittenden et al. 1980; Wernicke 1981) and subsequent recognition worldwide, “detachment faults” have been the center of heated debate. Detachment faults (figure 3.1) are gently dipping, commonly domed, fault surfaces of large aerial extent along which a significant part (commonly 5–15 km) of the crustal column is missing due to large-magnitude slip (typically 10–50 km). Debate centers on whether or not these faults formed and/or slipped as “low-angle normal faults” (dip<30º), because standard fault mechanical theory does not allow such orientations (Anderson 1942)...

While the uniform stretching model (McKenzie 1978) and its derivatives have been applied with considerable success to the formation of intracontinental rift basins, the mechanism for the formation of rifted continental margins is at best controversial. Rifted margins have traditionally been assumed to form by extreme extension and thinning of continental lithosphere (Le Pichon and Sibuet 1981), ultimately leading to the initiation of seafloor spreading at high stretching factor. Recent work on the northwest Australian rifted continental margin (Driscoll and Karner 1998; Baxter et al. 1999) and the Norwegian rifted continental margin (Roberts et al. 1997) suggests that the stretching...

The seismogenic zone is where earthquakes occur. Because earthquakes are rapid shear slip on nearly planar faults, a region with just one active fault has a planar seismogenic zone. However, in many instances we think of the seismogenic zone as a volume that includes the active fault and surrounding rock. The horizontal bounds on this volume are quite flexible–it may extend across entire continents or plates. In this context, the seismogenic zone is the rock volume capable of seismicity. We usually place more emphasis on the depth limits of the seismogenic zone—especially the deeper depth limit. This emphasis...

In this chapter we discuss changes downdip on the subduction thrust interface or in adjacent rocks that control whether or not portions of the thrust are seismogenic. The main seismogenic zone appears to be continuous between upper and lower slip stability transitions (Scholz 1990). Therefore, of special importance are the controls of the updip limit and downdip limits to the seismogenic zone (Shimamoto et al. 1993; Tichelaar and Ruff 1993; Hyndman and Wang 1993; Hyndman et al. 1997). The updip or seaward limit is important for tsunami generation. Larger tsunamis are generated if the great earthquake rupture extends updip close...

Convergent orogens present a particularly difficult problem for Earth scientists interested in the mechanics of crustal deformation. The deformation associated with plate convergence is intense and widespread, in many cases deforming the lithosphere for hundreds of kilometers from a plate boundary. In addition, lithospheric deformation associated with convergent orogenesis is diverse and no single model for the mechanical processes of orogeny is applicable to all convergent systems. The challenge to mechanical modelers is to find or adapt numerical tools capable of simulating these mechanical processes. Finite-element methods have proven to be a versatile and powerful method of analysis and have...

Characterizing the structure of large-displacement, plate-boundary fault zones is central to the MARGINS initiative to understand the mechanisms that allow continental lithosphere to deform by weak tectonic forces, strain partitioning, and movement of fluids during margin formation. At many boundaries, plate motions primarily are accommodated along large fault zones that achieve significant displacement over time. In addition, fluid migration through the crust often is intimately linked to the fluid-flow properties of these zones. At the crustal scale, faults may be idealized as simple discontinuities, or surfaces, between relatively rigid blocks along which shear displacement has occurred. Considerable work has elucidated...

Fault mechanics is based on two central premises: the Coulomb failure criterion, which defines the geometrical relations of faults with the orientations of the principal stresses that formed them (Anderson 1951), and a simple friction law for rock (Byerlee 1978) that defines the stresses needed to produce continued slip on them.

There has been a long-standing controversy, lasting for more than three decades, as to whether the Byerlee friction law actually applies to faults, or at least to all faults. This controversy was first centered on the San Andreas fault (SAF) of California, for which evidence has been marshaled (e.g.,...

A small amount of melt influences the elastic (reversible and time-independent), anelastic (reversible but time-dependent), and plastic or viscous (irreversible and time-dependent) deformation behavior of partially molten rocks. These material properties govern seismic velocity and seismic attenuation as well as the small-and large-scale flow behavior of mantle rocks. At the same time, deformation directly affects the distribution of melt in a partially molten rock. Consequently, the material properties of the rock are affected by the process of deformation.

In this chapter, we address three aspects of deformation of partially molten rocks. First, new experimental results are presented on anelastic and...

Fluid flow in rocks has far-reaching implications for seismogenic (Miller and Nur 2000; Rice 1992; Sibson 1981), sedimentary (Berner 1980; Etheridge et al. 1984), and metamorphic processes (Etheridge et al. 1984; Wood and Walther 1986). Because the physical properties of rocks strongly depend on porosity and pore geometry (e.g., Gangi 1979; Shankland et al. 1981; Simmons and Richter 1976; Walsh 1981) and because mechanical and thermal loads can substantially alter the pore geometry, mechanical forces directly affect transport properties. Conversely, rock strength is profoundly affected by pore fluids owing to diverse mechanical and chemical interactions (Bredehoeft and Hanshaw 1968; Carter...