Transport properties and its implication of pore pressure change - - PowerPoint PPT Presentation

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Transport properties and its implication of pore pressure change due to frictional heating during 1999 Taiwan Chi-Chi earthquake

Wataru Tanikawa (Kochi core research center / JAMSTEC） Toshihiko Shimamoto (Kyoto University)

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1999 T aiwan Chi-Chi E ar thquake

Ma et al. 2003

September 20, 1999 - Mw 7.6 Rupture of Chelungpu Fault Propagation from South to North Remarkable difference between N – S

Acceleration Velocity Displacement

Zhang et al. 2003

North South

Displacement Large -10m Small Velocity Large – 4.5m/s Small Acceleration Small Large High freq. radiation Low level

Stress Drop

Large Small

Que stion to be Solve d

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What made the contrast between North and South? What caused such a large displacement at Northern portion? Variation of fault rock property and Dynamic fault weakening mechanism

・ Melting (Hirose and Shimamoto, 2005) – Psuedotachylyte is rare in fault zones. ・ (Elast) hydrodynamic lubrication (Ma et al., 2003) – Fault rocks behaves as viscous? ・ Acoustic fluidization (Melosh, 1996) – Difficult how to identify – injection vein? ・ Thermal pressurization (Lachenbruch 1980) Current researches related to the Chelungpu Fault

Borehole temperature observation (Kano et al. 2006) - Low friction during slip event → Dynamic weakening mechanism effectively occurred? Core observation (Hirono et al. 2006) - Temperature doesn’t rise to melting point → Melt weakening is ineffective?

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Conc e pt of T he r mal Pr e ssur ization

Critical Parameters for TP ・ Diffusion parameter

• Permeability, Specific storage

・ Heat source parameter

• Shear strength, Thickness of fault core

Fault zone （ fault breccia） Fault core (fault gouge) ⇒Heat source

Velocity Thickness Strain distribution

Frictional Heating (during earthquake) ↓ Thermal expansion of pore water ↓(Undrained condition) Pore pressure generation ↓ Reduction of effective pressure ↓ Dynamic fault weakening ↓ Unstable → Large slip?

Slip Displacement (m) Shear stress (MPa)

Stress drops due to pore pressure generation

Pore pressure generation (MPa)

• Stress change at the fault zone-

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20 40 60

km Taipei Tainan Kaoshung Taitung

Eurasian Plate Philippine Sea Plate Manila Trench

Taichung

STUDY AREA

8.2 cm/yr Ryukyu Trench

Northern Hole Southern hole

Chelungpu Shuichangliu

Re se ar c h Ar e a

1)Depth Variation Chelungpu Fault Shuangtung Fault Shuichangliu Fault

(Stratigraphic cross section, Vitrinite reflectance)

2)Along-Fault Variation (borehole sample) Northern site (Fengyuan 400m) Southern site (Nantou 200m) TCDP - (Dakeng A:2000m, B:1350m)

Shuangtung

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Candidate1(329 - 330 m)

Thin clayey fault gouge (7 mm)

Slip plane?

10m random oriented fault breccia Siltstone/Sandstone

広い温度異常が確認280m～340m 3 possible candidates for slip zone - fault zones are developed within siltstone →Still under discussion which is the best choice!?

Candidate2 (224.55 – 224.75 m)

Fault breccia

No strong shear deformation zone Candidate3（ 405m)

Thick fault gouge（ 50cm） Deformed sandstone

Very thin hard black material (ultra cataclasite?)

Siltstone Siltstone Siltstone

Che lungpu F ault-Nor the r n bor e hole

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Fault breccia and fractured hostrock Black Layers

Boundary between Pleistocene and late Miocene

sediment.

8 m thickness of the clay-rich foliated fault gouge. Black layers（

ultra cataclasite） are developed in the both boundary of the thick foliated fault gouge (23 mm thick).

10 20 30 40 50 60 70

23±13 mm 650 450 250 10 90

thickness (mm)

Shuangtung F ault-outc r

• p

10 m-thickness clayey foliated fault gouge distance (cm)

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Experimental condition

Pore Fluid - N2 gas （ low viscosity） Temperature - room temperature Confining pressure - 0 ~ 200 MPa (12km) Fluid pressure - 0 ~ 2 MPa Sample size – φ20mm ×Length 10 - 40 mm

Method for measurements

Permeability - steady state gas flow method using accurate gas flow meter (ADM2000, Alicat flowmeter) Gas permeability is arranged to water permeability using the Klinkenberg equation. Porosity - calculated by the pore pressure change under undrained condition Specific storage- approximated by drained pore compressibility that is estimated from porosity test

f φ

φβ β Ss + = 1 1

=

∂ ∂ − − =

p φ

Pc φ φ β

Ss: Specific storage（ Pa-1) βf: Fluid compressibility(Pa-1） φ : Porosity Pc: Confining pressure p: Pore pressure

T r anspor t Pr

• pe r

ty T e st

Cylindrical samples Flow meter Pressure vessel

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Effective Pressure （ MPa） Effective Pressure （ MPa） Porosity （ %）

E xample of E xpe r ime nt – p

e r m e a b i l i t y & p

• r
• s

i t y

Permeability （ m2）

Applied for Thermal Pressurization analysis

Northern Shallow borehole for Chelungpu Fault

k2 k1

50 100 150 10

• 19

10

• 18

10

• 17

10

• 16

10

• 15

10

• 14

10

• 13

10

• 20

50 100 150 200

φ1 φ2

5 10 15 20 25 30

1.Strong sensitivity for effective pressure 2.Elast-plastic behaviors Proper description of parameters as a function of pressure is important!

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Distance from the fault (m) Permeability （ m2） Depth (m)

Northern borehole （

329m depth）

Southern borehole ◆Permeability for fault rock is larger in Southern site (one order). ◆Permeability for wall rock is larger in Southern site.

(326.5m depth) (305.5m)

(fault breccia) (conglomerate)

Pe r me ability Str uc tur eⅠ- A

l

• n

g F a u l t V a r i a t i

• n

Permeability （ m2）

Chelungpu Fault

浸透係数（ m2）

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Deep?

Shuangtung Fault Shuichangliu Fault

Distance from fault core（ m）

Chelungpu Fault < Shuangtung Fault • Shuichangliu Fault Permeability variation within fault zone is small

fault zone

Distance from fault core（ m） Distance from fault core（ m）

Pe r me ability Str uc tur eⅡ- D

e p t h V a r i a t i

• n

Shallow?

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Small difference of specific storage among the faults, within a fault zone, and between fault and host rocks. Most of them are around 10-9 Pa-1.

Specific storage (Pa-1)

Chelungpu Fault Shuangtung Fault Shuichangliu Fault

Spe c ific Stor age - D

e p t h V a r i a t i

• n

Distance from the slip surface（ m） Specific storage (Pa-1) Distance from the slip surface（ m） Specific storage (Pa-1)

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Shear stress Vertical stress Gouge material (1.5~2.0 g)

Gabbro blocks

Bi-axial typical frictional test

High Velocity Low Velocity

Slip velocity

0.1~1 m/s 0.1~100μm/s

Vertical stress

1 MPa 0 ~60MPa

Slip distance

∞ 20mm

F r ic tional Pr

• pe r

ty T e st

High shear velocity machine

Teflon-sleeve Vertical Stress Rotation Assembly of high frictional test for fault gouge Cylindrical host rock Gouge material（ 2g）

Designed by Shimamoto at Kyoto Univ.

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・ Stable friction achieved from 10 mm ・ Chelungpu > Shuangtung > Shuichangliu ・ Wet gouge < Dry gouge （ except South) ・ South - Velocity weakening ⇔ North - Velocity hardening

0.2 0.3 0.4 0.5 0.6 0.7 0.8 1 2 3 4

Frictional coefficient Dry Wet Chelungpu ‐ South Chelungpu ‐ North Shangtung Shuichangliu

• 0.01
• 0.005

0.005 0.01

a – b Velocity weakening Velocity hardening

Summe r y of L

• w Ve loc ity F

r ic tion

Slip displacement (mm) Vertical stress (MPa) Frictional coefficient

shear load cycles velocity step test

convention al H.S.H test

5 1 0 1 5 2 0 0 . 1 0 . 2 0 . 3 0 . 4

B A F 0 9 9

5 1 0 1 5 2 0

Hold-slide- hold test Velocity step test

Shear cycles at high vertical stress

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Chelungpu Fault – Southern Shallow core

(Black Gouge, 176.75 ~ 176.83m)

slip distance（ m） frictional coefficient

Low velocity frictional test 1)Dc 10 µm～1 mm 2)µd 0.5 ~ 0.85 １ ） Large peak friction～１ ２ ） Rapid reduction with slip ⇒ stable ３ ） Large weakening distance Dc～10m ４ ） Low steady state friction µd～0.2 Dc:Slip weakening distance Peak friction µp

Steady state frictional coefficient µd

0.6 MPa 0.9 MPa slip velocity： 1 m/s dry condition Temperature rise < 300oC

(Mizoguchi 2005) ⇒ Gouge

does not melt ⇒ What weakening mechanism?

High Ve loc ity F r ic tional Be havior for F G

→video image

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Chelungpu Fault - North

Grayish Gouge（ 285m）

Chelungpu Fault - South

Black Gouge (176.75-176.83m)

Shuangtung Fault Brownish Gouge Shuichangliu Fault Black Gouge Slip Distance （ m） Frictional Coefficient Frictional Coefficient

CONDITION

・ Slip velocity:1 m/s ・ Vertical stress:1MPa ・ Room Temperature ・ Dry gouge

0.6 MPa 0.6 MPa 0.9 MPa 0.6 MPa 0.9 MPa 0.6 MPa 0.9 MPa 0.6 MPa 0.9 MPa

Slip Distance （ m） Frictional Coefficient Slip Distance （ m） Frictional Coefficient Slip Distance （ m）

・ All gouges show similar behaviors ・ Dc － 6 ~ 13m． ・ South is largest

F ault Gouge Var iation for H-V F r ic tion

However weakening mechanism is not researched in detail! →Hydrodynamic lubrication? →Tribo-chemical reaction with heating?

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( )

⎟ ⎟ ⎠ ⎞ ⎜ ⎜ ⎝ ⎛ ⎟ ⎟ ⎠ ⎞ ⎜ ⎜ ⎝ ⎛ ∂ ∂ µ ∂ ∂ + ∂ ∂ γ − γ φ ⎟ ⎟ ⎠ ⎞ ⎜ ⎜ ⎝ ⎛ ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ ∂ φ ∂ + φβ = ∂ ∂ x P k x t T P t P

f T f

1

( ) W

V P A

d

− = σ µ ⎟ ⎟ ⎠ ⎞ ⎜ ⎜ ⎝ ⎛ ∂ ∂ + = ∂ ∂

2 2

1 x T A c t T κ ρ

Heat production rate Heat generation and diffusion Fluid flow and Pp generation

1D heat and fluid diffusion equation

Lachenbruch (1980) Mase and Smith (1987)

( )

( )

⎟ ⎠ ⎞ ⎜ ⎝ ⎛ ⋅ − + = Dc d . ln exp µ µ µ µ

ss p ss d

05 High velocity frictional behavior

µss

ss

µ p

Frictional coefficient Slip distance（ m）

dc dc

＋

Laboratory results

(Effective pressure functions)

Shear Stress Change τ= (Pc-Pp)×μd

T he r mal Pr e ssur ization Analysis

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Slip distance (m) Shear strength／Initial shear strength Slip distance (m)

1 2 3 4 5 6

TPなし

深度 (km)

Without TP Fault weakening due to TP Slip Velocity－1 m/s Thickness of fault－20 mm Small Dc at depth Shear strength／Initial shear strength

T P R e sult Ⅰ- Pp Ge ne r ation Ⅰ

Chelungpu Fault – North Chelungpu Fault – South

TP is ineffective!! ⇒ Weakening is due to high velocity (mechanical?) weakening TP is effective!! ⇒ Weakening is accelerated with depths．

no TP

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1 2 3 4 5 6

TPなし

深度 (km)

Slip displacement (m) Shear strength／Initial shear strength Slip displacement (m) Shear strength／Initial shear strength

T P R e sult Ⅱ-Pp Ge ne r ation Ⅱ

Slip Velocity－1 m/s Thickness of fault－20 mm

Shuangtung Fault Shuichangliu Fault

TP is relatively effective (Similarity to Northern Chelungpu Fault) TP is much effective !!

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T P R e sult Ⅲ - T e mpe r atur e R ise

200 400 600 800 1000 2 4 6 8 10

1 2 3 4 5

depth (km)

6 slip rate =1 m/s deformation zone = 20 mm

2 4 6 8 10 200 400 600 800 1000

1 2 3 4 5

depth (km)

6

2 4 6 8 10

1 2 3 4 5

depth (km)

6

200 400 600 800 1000 2 4 6 8 10 200 400 600 800 1000

1 2 3 4 5

depth (km)

6

Chelungpu Fault – North Shuangtung Fault Shuichangliu Fault

Temperature rise (oC) Temperature rise (oC) Temperature rise (oC) Temperature rise (oC)

Reducing shear strength of

• fault. Low, and relatively

low temperature rise in Shuangtung, and Northern Chelungpu Faults .

TP effective regime TP ineffective regime Rapid temperature rise easily reaches to melting point.

Chelungpu Fault – South

Slip displacement (m) Slip displacement (m) Slip displacement (m) Slip displacement (m)

T P R e sult Ⅳ - Impor tanc e of Width

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TCDP-Hole B 1194m

Width of the fault core is directly related to heating rate, and identification of the shear zone is important (though it is difficult).

BM disk（20mm thickness）

200 400 600 800 1000

10 20 30 40 100 200 width (mm)

1 2 3 4 5

slip rate =1 m/s depth = 5 km

Slip displacement (m) Temperature rise (oC)

10 20 30 40 100 200 width (mm)

0.2 0.4 0.6 0.8 1 1 2 3 4 5

slip rate =1 m/s depth = 5 km

Shear strength／Initial shear strength Slip displacement (m)

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North South Depth Remark

Permeability （ m2） 10-16~10-17 10-15~10-16 10-16~10-18 North < South Specific storage （ Pa-1） Small difference among faults （ 10-9 Pa-1） Relatively large frinction in Southern Chelungpu Fault TP analysis Relatively effective Ineffective Effective Possible existence of

• verpressure at depth might

be negative influence for TP.

μdry

0.7 0.7 0.5 ~0.6 Reduction in 50% at wet condition

a-b

High velocity friction Similar behavior （ exponential decay curve， Low steady state friction， Large initial friction） Low velocity friction + － +

Permeability variation ⇒ TP variation ⇒ Explain the difference between N-S? TP might be effective at depths（ Overpressure can not be neglected） . South is unstable ⇒ Consistent with initiation of EQ from the south?

Summe r y Ⅰ- fault var

iation

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Dc = 5.06m

• Trac. Drop =

4.5 MPa

Inversion analysis （ several cm to 10 m）

After Ma et al. (2005) After Jim Mori (2005)

Dc = 2.6 m

slip (m) (After Zheng et al. 2003)

Dc = 6.26 m

slip distance (m) normalized shear strength

Chelungpu Fault North

slip distance (m)

frictional coefficient

High velocity friction TP analysis Dc=6 to 13 m Dc=1 to 5 m

Summe r y Ⅱ-T

P vs Se ismic Data

1.Weakening distances,Dc, evaluated from TP analysis are similar order to that evaluated from seismic inversion analysis.

• 2. Without thermal

pressurization, we can account for the Dc from High velocity behavior. 3.Stress drop between TP and seismic data has gap.