Earth's crust not only deforms through hazardous earthquakes or aseismic motion, but also through transient episodes of deformation that can be measured with global positioning systems and detected in subtle signals in seismometers. The best documented settings for such "slow slip events" and associated "tremor" are subduction zones, where transitions between stable and unstable frictional sliding are thought to lead to nearly episodic slip. Such slip may well load the areas of the slab interface that cause destructive earthquakes. However, deep in subduction zones, materials are thought to deform viscously rather than frictionally. Outcrops of a deep mountain belt in the southern Andes preserve excellent geological examples of such viscously deformed crustal materials. These ductile shear zones are made of mixtures of strong and weak materials, and are cut by syn-tectonic fractures. Using geological observations and an analytical expression for coupled viscous and plastic deformation, slow-slip events similar to those observed in modern subduction zones can be modeled. Combining geological observation and the model provides a nice explanation for deep slow slip events, and may be broadened to other areas where transient creep arises through mixtures of materials with contrasting strength.
Oblique rifting ruptures continents: Example from the Gulf of California shear zone Scott E.K. Bennett and Michael E. Oskin, Department of Earth and Planetary Sciences, University of CaliforniaDavis, 1 Shields Avenue, Davis, California 95616, USA; firstname.lastname@example.org; email@example.com. Posted online 10 January 2014, http://dx.doi.org/10.1130/G34904.1.
The example of the Gulf of California Shear Zone demonstrates that the degree of rift obliquity play
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