Coseismic recrystallization during shallow earthquake slip
- Authors
- Smith, S. A. F.; Di Toro, G.; Kim, S.; Ree, J-H.; Nielsen, S.; Billi, A.; Spiess, R.
- Issue Date
- 1월-2013
- Publisher
- GEOLOGICAL SOC AMER, INC
- Citation
- GEOLOGY, v.41, no.1, pp.63 - 66
- Indexed
- SCIE
SCOPUS
- Journal Title
- GEOLOGY
- Volume
- 41
- Number
- 1
- Start Page
- 63
- End Page
- 66
- URI
- https://scholar.korea.ac.kr/handle/2021.sw.korea/104297
- DOI
- 10.1130/G33588.1
- ISSN
- 0091-7613
- Abstract
- Solidified 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 mu m were confined 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 reflective principal slip surfaces lined by polygonal grains <1 mu pm in size. The principal slip surfaces were flanked by <300 mu m thick layers of dynamically recrystallized calcite (grain size 1-10 mu m) containing well-defined 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.
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