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

Introduction 2 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 fault

Introduction 450 m 211 m 3

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 4 [Han et al. 2010]

Methods Samples : For friction tests – Southern : dark gray ultracataclasite from m depth – Northern : clay-rich fault gouge from 286 m depth and 303 m depth For transport property – Southern : m depth – Northern : 40.5 – m depth 5

Methods X-Ray Diffraction Southern: (A)Quartz, potassium feldspar Northern: (B,C)smectite, illite, kaolinite 6

Methods Low-Velocity Friction Test Double-direct shear apparatus 7 Slide-Hold-Slide test [Shimamoto]

Methods High-Velocity Friction Tests High-speed rotary-shear testing apparatus 8 Rotational speed of 1200 rpm Normal stress from MPa

Methods Transport Property Measurements – Permeability Darcy’s law : Klinkenberg equation : – Porosity Boyle ‘s law : – Specific Storage 9

Results High-Velocity Friction V=1.04 m/s Slip-weakening

Results Low-Velocity Friction

Results Low-Velocity Friction Tests velocity-dependent friction law 12

Results Permeability 13 South > North

Results Permeability distributions 14 Hanging wall footwall

Results Porosity 15 8~48%

Results Specific Storage 16

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: 17 Heat production Heat transfer

Thermal Pressurization Analysis The change in pore pressure depends on temperature change and Darcian fluid flux as follow : 18 T changeFluid flow

Analysis Results 19

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 20

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 21

Discussion Assuming at the hypocentral depth of the Chi-Chi earthquake T= ℃,vertical stress MPa – 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 22

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 23

Thanks for your attention. 24