thwestern U.S. and Canada is in the same sense and at nearly the same rate as the motions calculated from Global Positioning System (GPS) over the past 15 years. Motion of the ancestral arc can be explained by clockwise rotation of the leading edge of North America at 1.0 degree/m.y. over the magma source generated by the subducting plate, which is itself moving westward 1 to 4.5 km/m.y. as it slowly sinks into the mantle. The remarkable similarities between post-16 m.y. arc migration, paleomagnetic rotation, and modern GPS block motions indicate that the block motions from decadal GPS can be used to calculate meaningful long-term crustal strain rates and earthquake hazards.
Silica gel formation during fault slip: Evidence from the rock record
J.D. Kirkpatrick et al., Dept. of Geosciences, Colorado State University, 1482 Campus Delivery, Fort Collins, Colorado 80523, USA. Published online 22 July 2013, http://dx.doi.org/10.1130/G34483.1.
This open-access article by J.D. Kirkpatrick and colleagues discusses the dynamic reduction of fault strength as a key process during earthquake rupture. Many mechanisms for causing coseismic weakening have been proposed based on theory and laboratory experiments, including silica gel lubrication. However, few have been observed in nature. Here, Kirkpatrick and colleagues report on the first documented occurrence of a natural silica gel coating a fault surface at the Corona Heights fault slickenside in San Francisco, California, USA.
Comparison of microstructures in superplastically deformed synthetic materials and natural mylonites: Mineral aggregation via grain boundary sliding
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Takehiko Hiraga et al., Earthquake Research Institute, University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-0032, Japan. Published online 22 July 2013, h
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