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Amici S.,Instituto Nazionale Of Geofi Sica E Vulcanologia Ingv | Turci M.,University of Bologna
GIM International | Year: 2014

Insight into signs that prelude volcanic eruptions is key for protecting the lives, livestock and property of those living in the vicinity of a volcano. One key indicator is temperature rise. Using Mount Etna as a test site, the authors show that an unmanned aerial system (UAS) equipped with a thermal infrared sensor generates data similar to temperature data acquired by ground-based stations while avoiding safety risks for volcanologists.

Kuo L.-W.,National Taiwan University | Kuo L.-W.,Chinese Academy of Geological Sciences | Li H.,Chinese Academy of Geological Sciences | Smith S.A.F.,Instituto Nazionale Of Geofi Sica E Vulcanologia Ingv | And 9 more authors.
Geology | Year: 2014

The Longmenshan fault that ruptured during the 2008 Mw 7.9 Wenchuan (China) earthquake was drilled to a depth of 1200 m, and fault rocks including those in the 2008 earthquake slip zone were recovered at a depth of 575-595 m. We report laboratory strength measurements and microstructural observations from samples of slip zone fault rocks at deformation conditions expected for coseismic slip at borehole depths. Results indicate that the Longmenshan fault at this locality is extremely weak at seismic slip rates. In situ synchrotron X-ray diffraction analysis indicates that graphite was formed along localized slip zones in the experimental products, similar to the occurrence of graphite in the natural principal slip zone of the 2008 Wenchuan rupture. We surmise that graphitization occurred due to frictional heating of carbonaceous minerals. Because graphitization was associated with strong dynamic weakening in the experiments, we further infer that the Longmenshan fault was extremely weak at borehole depths during the 2008 Wenchuan earthquake, and that enrichment of graphite along localized slip zones could be used as an indicator of transient frictional heating during seismic slip in the upper crust. © 2013 Geological Society of America.

Smith S.A.F.,Instituto Nazionale Of Geofi Sica E Vulcanologia Ingv | Di Toro G.,Instituto Nazionale Of Geofi Sica E Vulcanologia Ingv | Di Toro G.,University of Padua | Kim S.,Korea University | And 4 more authors.
Geology | Year: 2013

Solidifi ed frictional melts, or pseudotachylytes, remain the only unambiguous indicator of seismic slip in the geological record. However, pseudotachylytes form at >5 km depth, and there are many rock types in which they do not form at all. We performed low- to high-velocity rock friction experiments designed to impose realistic coseismic slip pulses on calcite fault gouges, and report that localized dynamic recrystallization may be an easy-to-recognize microstructural indicator of seismic slip in shallow, otherwise brittle fault zones. Calcite gouges with starting grain size <250 μm were confi ned up to 26 MPa normal stress using a purpose-built sample holder. Slip velocities were between 0.01 and 3.4 m s-1, and total displacements between 1 and 4 m. At coseismic slip velocities ≥0.1 m s-1, the gouges were cut by refl ective principal slip surfaces lined by polygonal grains <1 μm in size. The principal slip surfaces were fl anked by <300 μm thick layers of dynamically recrystallized calcite (grain size 1-10 μm) containing well-defi ned shape- and crystallographic-preferred orientations. Dynamic recrystallization was accompanied by fault weakening and thermal decomposition of calcite to CO2 + CaO. The recrystallized calcite aggregates resemble those found along the principal slip surface of the Garam thrust, South Korea, exhumed from <5 km depth. We suggest that intense frictional heating along the experimental and natural principal slip surfaces resulted in localized dynamic recrystallization, a microstructure that may be diagnostic of seismic slip in the shallow crust. © 2012 Geological Society of America.

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