Date:7/12/2012

hey are products of massive dynamic fragmentation that took place during mega-earthquakes within the upper part of Earth's crust. However, it was quite possible that weathering and other near-surface processes strongly affected the original pulverization structure. New supporting evidence for the origin of the pulverization by catastrophic events was discovered in rocks at a ~5 km depth that were retrieved by drilling through a deep fault zone. The rock samples included fine-grained carbonates that were well-compacted and homogenous. Analysis of these samples revealed a unique pattern of micro-fractures that are characteristic of hierarchical branching of tight tensile cracks. This unique branching pattern is a well-known effect of instability in rapid fractures that propagate near elastic wave velocities. Thus, the deep burial setting, which has preserved these fracture patterns, now provides direct evidence that pulverization is indeed an effect of dynamic loading and fracturing. The significant depth at which these fractures were found indicates that a large part of earthquake energy may be absorbed by off-fault deformation.

---

Active extension in Taiwan's pre-collision zone: A new model of plate bending in continental crust
Ryan Lester et al., Institute for Geophysics, The University of Texas, J.J. Pickle Research Campus, Building 196, 10100 Burnet Rd., Austin, Texas 78758-0000, USA. Posted online 12 July 2012; doi: 10.1130/G33142.1.

Collisions between continental margins and volcanic arcs mark the closing of ocean basins, the rise of mountain belts, and the growth of continents. However, there are only a handful of modern-day examples of active arc-continent collision. Taiwan is one such example, where the southern Chinese continental margin is currently colliding with the Luzon arc at the Manila trench. A new seismic image and numerical models indicate that such collisions may be preceded by bending and stretching of the
'/>"/>

Contact: Kea Giles kgiles@geosociety.org Geological Society of America Source:Eurekalert

0 GOOD

Page: 1 2 3 4
Related biology news :

1. How old are these rocks, how were they made, and how long ago did these geologic changes happen?
2. Our coral reefs: In trouble - but tougher than we thought
3. Viruses linked to algae that control coral health
4. Scientists join forces in call for action to save coral reefs
5. New research finds increased growth responsible for color changes in coral reefs
6. 12th International Coral Reef Symposium
7. Topics to be discussed during July International Coral Reef Symposium
8. Coral reef experts to present latest coral reef science during July symposium
9. Florida Tech biological sciences professor earns $257,000 NSF grant to study coral diseases
10. Pacific islands may become refuge for corals in a warming climate, study finds
11. Under climate change, winners and losers on the coral reef