frictional and transport properties of the chelungpu fault from shallow borehole data and their...
TRANSCRIPT
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.