Conversion of wet glass to melt at lower seismogenic zone conditions: Implications for pseudotachylyte creep

Geophysical Research Letters
By: , and 

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Abstract

Coseismic frictional melting and the production of quenched glass called pseudotachylyte is a recurring process during earthquakes. To investigate how glassy materials affect the postseismic strength and stability of faults, obsidian gouges were sheared under dry and wet conditions from 200°C to 300°C at ~150 MPa effective normal stress. Dry glass exhibited a brittle rheology at all conditions tested, exhibiting friction values and microstructures consistent with siliciclastic materials. Likewise, wet glass at 200°C exhibited a brittle rheology. In contrast, wet gouges at 300°C transitioned from brittle sliding to linear‐viscous (Newtonian) flow at strain rates <3 × 10−4 s−1, indicating melt‐like behavior. The viscosity ranged from 2 × 1011 to 7.8 × 1011 Pa‐s. Microstructures show that viscous gouges were fully welded with rod‐shaped microlites rotated into the flow direction. Fourier transform infrared spectroscopy along with electron backscatter imaging demonstrate that hydration of the glass by diffusion of pore water was the dominant process reducing the viscosity and promoting viscous flow. As much as 5 wt % water diffused into the glass. These results may provide insight into postseismic‐slip behaviors and challenge some interpretations of fault kinematics based on studies assuming that pseudotachylyte formation and flow is solely coseismic.

Additional publication details

Publication type Article
Publication Subtype Journal Article
Title Conversion of wet glass to melt at lower seismogenic zone conditions: Implications for pseudotachylyte creep
Series title Geophysical Research Letters
DOI 10.1002/2017GL075344
Volume 44
Issue 20
Year Published 2018
Language English
Publisher American Geophysical Union
Contributing office(s) Earthquake Science Center
Description 8 p.
First page 10248
Last page 10255