Publication Date:
2017-04-04
Description:
Under extreme conditions like those encountered during earthquake
slip, frictional melt is likely to occur. It has been observed on
ancient faults that the melt is mostly extruded toward local extensional
jogs or lateral tension cracks. In the case of laboratory experiments
with a rotary shear apparatus, melt is extruded from the sample borders.
When this happens, a thin and irregular melt layer is formed whereby
the normal load is still in part supported by contact asperities under
an incipient yield condition (as in dry friction models), but also,
in the interstices between asperities, by the pressure of the viscous
fluid wetting the interface. In addition, roughness of the surface
is dynamically reshaped by the melting process of an inhomogeneous
material (polymineralic rock). In particular, we argue that the roughness
of the melting surface decreases with melting rate and temperature
gradient perpendicular to the fault. Taking into account the above
conditions, we obtain an expression for the average melt layer thickness
and viscous pressure that may be used in estimates of friction in
the presence of melt. We argue that the ratio of melt thickness to
roughness depends on sliding velocity; such a ratio may be used as
a gauge of slip-rate during fossil earthquakes on faults bearing pseudotachylite
(solidified melt). Finally, we derive an improved analytical solution
for friction in the presence of melt including the effect of roughness
evolution.
Description:
We acknowledge Takehiro Hirose for providing sample HVR 687. Stefan
Nielsen was granted by the MIUR project FUMO, and Giulio Di Toro and
Stefan Nielsen were granted by the European Research Council Starting
Grant Project 205175 (USEMS) and CA.RI.PA.RO. We thank Leonardo Tauro
for thin section preparation, Luca Peruzzo, Steven Smith and Piergiorgio
Scarlato for SEM facilities and Toshi Shimamoto for his constant support.
Finally, we are grateful to Nick Beeler and Chris Marone for their
constructive reviews.
Description:
Published
Description:
299–310
Description:
3.1. Fisica dei terremoti
Description:
JCR Journal
Description:
open
Keywords:
friction
;
roughness
;
melt
;
preferential melting
;
04. Solid Earth::04.06. Seismology::04.06.01. Earthquake faults: properties and evolution
Repository Name:
Istituto Nazionale di Geofisica e Vulcanologia (INGV)
Type:
article
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