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| Titel |
Transformation of fault slip modes in laboratory experiments |
| VerfasserIn |
Vasilii Martynov, Alexey Ostapchuk, Vadim Markov |
| Konferenz |
EGU General Assembly 2017
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 19 (2017) |
| Datensatznummer |
250143998
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| Publikation (Nr.) |
 EGU/EGU2017-7774.pdf |
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| Zusammenfassung |
| Slip mode of crust fault can vary because of many reasons. It’s well known that fault
structure, material of fault gouge, pore fluid et al. in many ways determines slip modes from
creep and slow slip events to mega-earthquakes [1-3]. Therefore, the possibility of fault
slip transformation due to external action is urgent question. There is popular and
developing approach of fluid injection into central part of fault. The phenomenon of
earthquakes induced due to pumping of water was investigated on small and large
scales [4, 5]. In this work the laboratory experiments were conducted to study the
evolution of the experimental fault slip when changing the properties of the interstitial
fluid.
The scheme of experiments is the classical slider-model set-up, in which the block under
the shear force slips along the interface. In our experiments the plexiglas block
8x8x3 cm3 in size was put on the plexiglas base. The contact of the blocks was filled
with a thin layer (about 3 mm thick) of a granular material. The normal load varied
from 31 to 156 kPa. The shear load was applied through a spring with stiffness
60 kN/m, and the rate of spring deformation was 20 or 5 mcm/s. Two parameters
were recorded during experiments: the shear force acting on the upper block (with
an accuracy of 1 N) and its displacement relatively the base (with an accuracy of
0.1 μm). The gouge was composed of quartz sand (97.5%) and clay (2.5%). As a
moisturizer were used different fluids with viscosity varying from 1 to 103 mPa x
s.
Different slip modes were simulated during slider-experiments. In our experiments slip
mode is the act of instability manifested in an increase of slip velocity and a drop of
shear stress acting on a movable block. The amplitude of a shear stress drop and
the peak velocity of the upper block were chosen as the characteristics of the slip
mode.
In the laboratory experiments, slip events of one type can be achieved either as regularly
recurring (regular mode) or as random stochastic (irregular mode). To investigate regularities
of transformation and get statistically correct results we simulated only regular mode. During
the experiments, after the establishment of a regular mode, we injected fluid into central part
of interblock contact. Varying injecting fluid we were able both to decrease and increase
amplitude of events. For example, after injection of 1 mPa x s fluid (water) in gouge,
moisturized with 100 mPa x s fluid (ethylene glycol), peak velocity rose by almost an
order. But after injection of an aqueous solution of starch (big viscosity and dilatant
rheology) amplitude decreased 1.5 times and then slip almost completely stabilized.
It’s probably connected with the viscosity of solution, which increases with quick
shift.
Time of injection also has the significant impact on the possibility of transformation and
its efficiency. Thus, it is well known that if the time of injection is in the vicinity of loss of
strength moment, any external influence only initiates slip events.
Preliminary results of our laboratory experiments show that the fluid injection can
both reduce the part of deformation energy going seismic wave radiation, and to
increase it. The most effective action observed in experinemts with injection of
dilatant fluid. Findings demonstrate the prospectivity of further research in this
direction.
The work was supported by the Russian Science Foundation (Grant No. 16-17-00095)
[1] Fagereng A., Sibson R.H. 2010. Melange rheology and seismic style. Geology.
Vol.38, p.751-754.
[2] Kocharyan G.G., et al. 2017. A study of different fault slip modes governed by the
gouge material composition in laboratory experiments. Geophys. J. Int. Vol.208, p.
521-528.
[3] Yamashita T. 2013. Generation of slow slip coupled with tremor due to fluid flow along a
fault. Geophys. J. Int. Vol.193, p.375–393.
[4] Guglielmi Y., et. al. 2015. Seismicity triggered by fluid injection-induced aseismic slip.
Science. Vol.348, p.1224-1226.
[5] Wei S., et al. 2015. The 2012 Brawley swarm triggered by injection-induced aseismic slip.
EPSL. Vol. 422, p.115-122. |
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