Journal of Geophysical Research Wataru Tanikawa , Toshihiko Shimamoto
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Transcript of Journal of Geophysical Research Wataru Tanikawa , Toshihiko Shimamoto
Frictional and transport properties of the Chelungpu fault from shallow borehole data and their correlation
with seismic behavior during the 1999 Chi-Chi earthquake
Journal of Geophysical Research
Wataru Tanikawa, Toshihiko Shimamoto
指導教授:董家鈞 老師報告者:陳宥任日期: 2010/12/16
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Introduction
small slip displacement (H: 3.5m, V: 4m)
large slip displacement (H: 9.8m, V: 5.6m)
High acceleration(1g)
Low acceleration(0.5g)
Chelungpu faultChelungpu fault
Introduction
450 m
211 m
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Introduction• Transport properties within a fault zone also
have important influence on dynamic slip motion
• Thermal pressurization mechanism is probably controlled primarily by transport properties
• Thermal pressurization [Sibson, 1973] : Increase pore pressure induced by frictional heating can cause fault weakening
[Han et al. 2010]
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Methods
• Samples :• For friction tests– Southern : dark gray ultracataclasite from 176.8 m
depth – Northern : clay-rich fault gouge from 286 m depth
and 303 m depth• For transport property– Southern : 30-194 m depth– Northern : 40.5 – 402.5 m depth
Methods
X-Ray Diffraction
Southern: (A)Quartz, potassium feldspar
Northern: (B,C)smectite, illite, kaolinite
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Methods
• Low-Velocity Friction Test
Double-direct shear apparatus
Slide-Hold-Slide test
[Shimamoto]
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Methods
• High-Velocity Friction Tests
High-speed rotary-shear testing apparatus
Rotational speed of 1200 rpmNormal stress from 0.6-0.9 MPa
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Methods
• Transport Property Measurements– Permeability• Darcy’s law :• Klinkenberg equation :
– Porosity• Boyle ‘s law :
– Specific Storage1 1 2 2P V =P V
kQ= ΔP
A ηLwater
gas water
bk =k 1+
P /2up downP
w p fSs=γ β +nβ
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Results
• High-Velocity Friction
V=1.04 m/s
0.8-1.2
0.2-0.4
Slip-weakening
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Results
• Low-Velocity Friction
0.7
0.7
0.4-0.5
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Results• Low-Velocity Friction Tests
*ss ss *
Vμ V -μ V = a-b ln
V
a-b >0 Velocity-Strengthening
a-b <0 Velocity-Weakening
velocity-dependent friction law
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Results
• Permeability South > North
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Results
Permeability distributions
Hanging wall
Hanging wall
footwall
footwall
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Results
• Porosity
8~48%
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Results
• Specific Storage w p fSs=γ β +nβ
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Thermal Pressurization Analysis
• Lachenbruch’s (1980) model : One-dimensional analysis of thermal pressurization process
• Temperature change is given by the sum of production term and heat transfer term as follow:
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T A κ Tt ρc ρc x
Heat production
Heat transfer
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Thermal Pressurization Analysis
• The change in pore pressure depends on temperature change and Darcian fluid flux as follow :
Φ 1p pP Pγ T kt Ss t Ss x η x
T change Fluid flow
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Analysis Results
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Discussion
• The high-velocity friction behavior is very different from low-velocity friction behavior– low-velocity friction coefficient
• North(wet)~0.4 ; South(wet)~0.7
– The high-velocity steady-state value of friction coefficient (0.2) is similar the earthquake
• Tanaka et al.[2006] reported in situ temperature deficits imply that dynamic friction was very low, the indicate that friction coefficient as low as 0.05 to 0.12– Slip-weakening
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Discussion
• Low velocity:– Northern gouge: velocity-strengthening – Southern gouge: velocity-weakening
• If the faulting mechanism is represented by the behavior of wet gouge– the velocity-weakening frictional behavior in the
south is consistent with the earthquake– Northern gouge exhibits velocity-strengthening
behavior is inconsistent with the large slip displacement
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Discussion
• Assuming at the hypocentral depth of the Chi-Chi earthquake T=200-300 ,vertical stress 120-150MPa℃– Thermally driven mineral transitions, such as
dehydrantion of smectite to illite
• Illite-rich gouge show velocity-strengthening behavior over the entire range of normal stress [Saffer and Marone,2003]
• Numerical model : large slip caused by thermal pressurization
• Northern controlled by thermal pressurization and material behavior
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Conclusions
• The behavior of fault gouge material from shallow boreholes during high-velocity slip is much different than during low-velocity slip
• Assuming wet gouge under low-velocity is consistent with the southern section
• Thermal pressurization caused large slip and illite-rich gouge caused velocity-strengthening in northern section
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• Thanks for your attention.