20061010WS-TAIWANinAIST 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)
20061010WS-TAIWANinAIST 1999 T aiwan Chi-Chi E ar thquake Acceleration Velocity Displacement � September 20, 1999 - Mw 7.6 � Rupture of Chelungpu Fault � Propagation from South to North � Remarkable difference between N – S North South Ma et al. 2003 Displacement Large -10m Small Velocity Large – 4.5m/s Small Acceleration Small Large High freq. Low level radiation Stress Drop Large Small Zhang et al. 2003
20061010WS-TAIWANinAIST Que stion to be Solve d 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?
20061010WS-TAIWANinAIST Conc e pt of T he r mal Pr e ssur ization Fault core (fault gouge) ⇒ Heat source Fault zone （ fault breccia ） Frictional Heating (during earthquake) ↓ Thermal expansion of pore water ↓ (Undrained condition) Pore pressure generation ↓ Velocity Reduction of effective pressure ↓ Thickness Strain distribution Dynamic fault weakening ↓ -Stress change at the fault zone- Unstable → Large slip? Pore pressure generation (MPa) Stress drops due Shear stress (MPa) to pore pressure Critical Parameters for TP generation ・ Diffusion parameter - Permeability, Specific storage ・ Heat source parameter - Shear strength, Thickness of fault core Slip Displacement (m)
20061010WS-TAIWANinAIST Re se ar c h Ar e a Eurasian Plate Northern Hole Taipei 0 20 40 60 STUDY km AREA Taichung Chelungpu Shuichangliu 1)Depth Variation Ryukyu Tainan Trench Taitung Kaoshung Chelungpu Fault 8.2 cm/yr Manila Trench Shuangtung Fault Philippine Sea Plate Shuichangliu Fault (Stratigraphic cross section, Vitrinite reflectance) 2)Along-Fault Variation (borehole sample) Southern hole Northern site (Fengyuan 400m) Southern site (Nantou 200m) TCDP - (Dakeng A:2000m, B:1350m) Shuangtung
20061010WS-TAIWANinAIST Che lungpu F ault-Nor the r n bor e hole 3 possible candidates for slip zone - fault zones are developed within siltstone → Still under discussion which is the best choice!? 広い温度異常が確認 280m ～ 340m Candidate1(329 - 330 m) 10m random oriented fault breccia Siltstone/Sandstone Slip plane? Candidate2 (224.55 – 224.75 m) Siltstone Fault breccia Siltstone No strong shear deformation zone Candidate3 （ Thin clayey fault gouge (7 mm) 405m) Thick fault gouge （ 50cm ） Siltstone Deformed sandstone Very thin hard black material (ultra cataclasite?)
20061010WS-TAIWANinAIST Shuangtung F ault-outc r op 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). 70 60 23±13 mm thickness (mm) 50 40 30 20 10 0 10 90 250 450 650 10 m-thickness clayey foliated fault gouge distance (cm)
20061010WS-TAIWANinAIST T r anspor t Pr ope r ty T e st Experimental condition Pore Fluid - N2 gas （ low viscosity ） Temperature - room temperature Confining pressure - 0 ~ 200 MPa (12km) Fluid pressure - 0 ~ 2 MPa Sample size – φ 20mm × Length 10 - 40 mm Cylindrical samples Flow meter 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 Ss: Specific storage （ Pa -1 ) = + Ss β φβ φ f β f : Fluid compressibility(Pa -1 ） ∂ φ φ : Porosity 1 = − β φ − ∂ φ Pc Pc: Confining pressure 1 = p 0 p: Pore pressure Pressure vessel
ime nt – p e r m e a b i l i t y & p o r o s i t y 20061010WS-TAIWANinAIST E xample of E xpe r Northern Shallow borehole for Chelungpu Fault 30 -13 10 25 -14 m 2 ） 10 % ） 20 Permeability （ -15 10 Porosity （ -16 15 10 -17 10 10 φ 2 -18 10 k1 φ 1 5 -19 10 k2 -20 0 10 0 50 100 150 0 50 100 150 200 Effective Pressure （ MPa ） Effective Pressure （ MPa ） Applied for Thermal Pressurization analysis 1.Strong sensitivity for effective pressure Proper description of parameters as a function of pressure is important! 2.Elast-plastic behaviors
e Ⅰ - A l o n g F a u l t V a r i a t i o n 20061010WS-TAIWANinAIST Pe r me ability Str uc tur Northern borehole （ 329m depth ） Southern borehole m 2 ） m 2 ） (305.5m) Permeability （ Permeability （ (326.5m depth) (conglomerate) (fault breccia) Distance from the fault (m) Depth (m) ◆ Permeability for fault rock is larger in Southern site (one order). ◆ Permeability for wall rock is larger in Southern site.
e Ⅱ - D e p t h V a r i a t i o n 20061010WS-TAIWANinAIST Pe r me ability Str uc tur Deep? Shallow? Chelungpu Fault Shuangtung Fault Shuichangliu Fault m 2 ） 浸透係数（ fault zone Distance from fault core （ m ） Distance from fault core （ m ） Distance from fault core （ m ） � Chelungpu Fault < Shuangtung Fault • Shuichangliu Fault � Permeability variation within fault zone is small
age - D e p t h V a r i a t i o n 20061010WS-TAIWANinAIST Spe c ific Stor Chelungpu Fault Specific storage (Pa -1 ) 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 . Distance from the slip surface （ m ） Shuangtung Fault Shuichangliu Fault Specific storage (Pa -1 ) Specific storage (Pa -1 ) Distance from the slip surface （ m ） Distance from the slip surface （ m ）
20061010WS-TAIWANinAIST F r ic tional Pr ope r ty T e st Bi-axial typical frictional test High shear velocity machine Shear stress Gabbro blocks Vertical stress Designed by Shimamoto at Kyoto Univ. Assembly of high frictional test for fault gouge Cylindrical Gouge material (1.5~2.0 g) host rock Rotation High Velocity Low Velocity 0.1~100 μ m/s Slip velocity 0.1~1 m/s Vertical Stress Vertical stress 1 MPa 0 ~60MPa ∞ Gouge material （ 2g ） Slip distance 20mm Teflon-sleeve
20061010WS-TAIWANinAIST Summe r y of L ow Ve loc ity F r ic tion 0 . 4 2 0 Frictional coefficient ・ Stable friction achieved from 10 mm 0 . 3 1 5 Vertical stress (MPa) ・ Chelungpu > Shuangtung > Shuichangliu ・ Wet gouge < Dry gouge （ Velocity step test Hold-slide- except South) 0 . 2 1 0 hold test convention ・ velocity step South - Velocity weakening al H.S.H Shear cycles at high ⇔ North - Velocity hardening test 0 . 1 5 test vertical stress B A F 0 9 9 shear load cycles 0 0 0 5 1 0 1 5 2 0 Slip displacement (mm) Velocity Dry Chelungpu 1 hardening Wet ‐ South Chelungpu 2 ‐ North Shangtung 3 Velocity Shuichangliu 4 weakening 0.2 0.3 0.4 0.5 0.6 0.7 0.8 -0.01 -0.005 0 0.005 0.01 a – b Frictional coefficient
20061010WS-TAIWANinAIST High Ve loc ity F r ic tional Be havior for F G Chelungpu Fault → video image – Southern Shallow core Peak friction µ p (Black Gouge, 176.75 ~ 176.83m) frictional coefficient slip velocity ： 1 m/s 0.6 MPa 0.9 MPa dry condition Steady state frictional Temperature rise < 300 o C coefficient µ d (Mizoguchi 2005) ⇒ Gouge does not melt ⇒ What weakening mechanism? Dc:Slip weakening distance slip distance （ m ） １ ） Large peak friction ～１ Low velocity frictional test ２ ） Rapid reduction with slip ⇒ stable 1) D c 10 µ m ～ 1 mm ３ ） Large weakening distance D c ～ 10m 2) µ d 0.5 ~ 0.85 ４ ） Low steady state friction µ d ～ 0.2
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