Presenter: Chien-Cheng Hung
Date: 2017/05/18
Abstract
Fault-origin pseudotachylyte is a solidified melt produced by frictional heating during big earthquakes. It is well-known as a seismic indicator which can provide information on earthquake physics. A new locality of pseudotachylyte-bearing fault, hosted in the Tananao granitic gneiss, was discovered in the Hoping area of Eastern Taiwan. To investigate the plausible dynamic frictional behavior of the Hoping pseudotachylyte, we perform rock friction experiments on granitic gneiss cores collected from the borehole in the Hoping area. All the mechanical data show similar frictional trends that the shear stress initially increases up to a peak value of ~0.6-1.0 (peak friction) and decreased with displacement to a steady state of ~0.3-0.45 from low to high normal stresses (3 to 30 MPa). It is notable that, at low normal stresses of 3 MPa, a transient increase of shear stress (friction bump) appears after peak friction. The micro-analytical results of the slip-stepping experimental products including in situ synchrotron XRD and FESEM-EDX show chemical and compositional variation in the matrix of melts. In particular, Transmission X-ray Microscope (TXM) on the matrix of melts shows the varied size distribution of remain quartz grains in the melt layer. It suggests that melts derived from flash heating with additive comminution products at initial small slip results in higher viscosity than the one generated from pure melting, plausibly due to Gibbs-Thomason effect. The presence of comminution, resulting in high viscous melts, seems to terminate seismic slip at low normal stresses, we surmise that comminution may hamper seismic slip in the initial earthquake propagation at shallow depth, even melt lubrication was operated afterword.
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