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Science 3 February 2006:
Vol. 311. no. 5761, pp. 647 - 649
DOI: 10.1126/science.1121012
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Reports

Natural and Experimental Evidence of Melt Lubrication of Faults During Earthquakes

Giulio Di Toro,1* Takehiro Hirose,2 Stefan Nielsen,3 Giorgio Pennacchioni,1 Toshihiko Shimamoto2

Melt produced by friction during earthquakes may act either as a coseismic fault lubricant or as a viscous brake. Here we estimate the dynamic shear resistance ({tau}f) in the presence of friction-induced melts from both exhumed faults and high-velocity (1.28 meters per second) frictional experiments. Exhumed faults within granitoids (tonalites) indicate low {tau}f at 10 kilometers in depth. Friction experiments on tonalite samples show that {tau}f depends weakly on normal stress. Extrapolation of experimental data yields {tau}f values consistent with the field estimates and well below the Byerlee strength. We conclude that friction-induced melts can lubricate faults at intermediate crustal depths.

1 Dipartimento di Geologia, Paleontologia e Geofisica, Università di Padova, 35137, Padova, Italy.
2 Division of Earth and Planetary Sciences, Graduate School of Science, Kyoto University, Kyoto 606–8502, Japan.
3 Research Unit RISSC Istituto Nazionale di Geofisica e Vulcanologia, Roma 1, 00143 Rome, Italy.

* To whom correspondence should be addressed. E-mail: giulio.ditoro{at}unipd.it

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