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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2

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.