A study on laboratory-derived friction laws and their application to seismic faulting in Taiwan (I)

Base on the combination of the Eurasia
and Philippine plate forms the Taiwan Island,
the disaster which is induced by fault
movement will be serious because the
earthquake focus is quit shallow and near the
city. The study of the friction characteristic of
the fault gouge is proposed by Dieterich,
etc(1994) that combines the speed and the state
parameter to propose the friction law. This
friction law offers a quite practical method to
study the earthquake. To explain the friction
law, most of the existing experimental studies
use the granular materials such as the granite
particle and the quartz sand. Most faults in
western Taiwan contain fault gouges, including
Chelungpu Fault, so that this research focuses
on the technical practicability to find out the
effect of clayey gouge and some other factors
which may control the slip stability. This
approach shows that the insight conclude the
underlying physics of a specific fault and the
parameters into the following rules.
Two main experiments are performed,
there are Slide-Hold-Slide tests (SHS tests) and
Velocity Stepping tests (VS tests), to determine
some friction parameters and to establish the
relation between different parameters in the
friction law. The experiments are carried out by
using triaxial apparatus on a 5mm-thick gouge
layer of remolded fault clayey gouge.
Slide-Hold-Slide tests are driven at a constant
velocity for each test, and it keeps a given
interval to restart at the driving velocities. The
results indicate that (1) the static friction
(healing) μsand the friction relaxation are
linearly increased with log-hold-time during
the quasi-stationary contact; (2) the fast slip
produces would have large static friction for a
given contact time, but the rate of healing β
would maintain constant at different operating
rates of displacements; (3) the drained volume
Δv is increased as the holding time in the
sample compression, and this behavior is
similar to the consolidation of soil mechanics.
For the Velocity Stepping tests, the effects on
the friction parameters are discussed by varying
the ratios of steps depending on velocity (10～
400), load velocity (0.005~5 mm/min), and the
accumulated slip in velocity stepping tests. The
results indicate that (1) the frictional stability
(a-b) is decreasing with shear strain, and the
positive value of (a-b) leads the fault gauge to
be “velocity-strengthening” behavior, which is
intrinsically stable; (2) frictional parameters a,
b, and (a-b) are not major influence of velocity;
(3) the critical slide distance Dc decreases with
the increasing ratio of the velocity steps.
Furthermore, the friction law is verified and
suitable for this research, and the fitting curve
from the experimental results has good
R-squared values. Finally, the relations between
parameters b=βln(10)and (a-b)=dμd/d V are
also established.