Structural evolution of the Nojima fault (Awaji Island, Japan) revisited from the GSJ drill hole at Hirabayashi

Boullier, Anne-Marie; Fujimoto, Koichiro; Ito, Hisao; Ohtani, Toshio; Keulen, Nynke; Fabbri, Olivier; Amitrano, David; Dubois, Michel; Pézard, Philippe

doi:10.1186/bf03353345

Cited by 19 publications

(7 citation statements)

References 25 publications

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“…All the gouge injections observed in FZA1111 are deformed and sheared together with the surrounding foliated sediments in a way similar to the compacted gouge, i.e., by the low strain rate pressure solution mechanism [ Durney , 1976; Rutter , 1976; Gratier , 1987; Le Guen et al , 2007]. By comparison with what has been described in the Nojima fault zone [ Boullier et al , 2004b], this pressure solution mechanism is interpreted as acting mostly during interseismic stages. Therefore, like the compacted gouges, the gouge injections should correspond to past earthquakes.…”

Section: Discussionmentioning

confidence: 94%

Microscale anatomy of the 1999 Chi‐Chi earthquake fault zone

Boullier

Yeh

Boutareaud

et al. 2009

Geochem Geophys Geosyst

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130

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[1] Two TCDP boreholes A and B were drilled in the northern part of the Chelungpu thrust fault where the Chi-Chi earthquake (21 September 1999, Mw 7.6) showed large displacement, low ground acceleration, and high slip velocity. In this paper, we describe the microstructures of the Chi-Chi Principal Slip Zone (PSZ) within black gouges localized at 1111 m depth in Hole A and at 1136 m depth in Hole B. In the FZA1111 the PSZ is a 2 cm-thick isotropic clay-rich gouge which contains aggregates formed by central clasts coated by clay cortex (clay-clast aggregates (CCAs)) and fragments of older gouges segregated in the top third of the PSZ. In FZB1136 the PSZ is 3 mm thick and is characterized by a foliated gouge displaying an alternation of clay-rich and clast-rich layers. The presence of CCAs, plucked underlying gouge fragments, gouge injections, and the occurrence of reverse grain size segregation of large clasts in the FZA1111 isotropic gouge suggest that the gouge was fluidized as a result of frictional heating and thermal pressurization. The foliated gouge in FZB1136 may be one locus of strain localization and related heat production. Small calcite veins present above the isotropic FZA1111 PSZ gouge and, characterized by an increasing strain with increasing distance away from the PSZ, are attributed to coseismic fluid escape from the pressurized gouge. The observed microstructures are interpreted in view of their seismic implications for the Chi-Chi earthquake in terms of slip weakening mechanisms by thermal pressurization, gouge fluidization, coseismic fluid distribution, and postseismic slip. Above the PSZ, several layers of compacted gouges containing deformed CCAs and gouge fragments correspond to several PSZ of past earthquakes similar to the Chi-Chi earthquake and display a fault-parallel cleavage resulting from a low strain rate pressure solution deformation mechanism that may be correlated to the interseismic periods.

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Section: Discussionmentioning

confidence: 94%

Microscale anatomy of the 1999 Chi‐Chi earthquake fault zone

Boullier

Yeh

Boutareaud

et al. 2009

Geochem Geophys Geosyst

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116

130

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“…Pseudotachylytes related to this deformation episode [ Boullier et al , 2001] were dated at 56 ± 4 Ma by fission tracks on zircons [ Murakami and Tagami , 2004]. The deformation was followed by an alteration producing laumontite [ Fujimoto et al , 2001] which indicates temperatures of 150°C–280°C [ Zen and Thompson , 1974, Boullier et al , 2004].…”

Section: Resultsmentioning

confidence: 99%

Healing microstructures of experimental and natural fault gouge

2008

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[1] The healing of fault gouge was studied by examining microstructures of naturally and experimentally produced granitoid fault rock. We performed deformation experiments on intact granitoid rock samples at T = 300-500°C, P c = 500 MPa, and _ e = 1.2 Â 10 À4 -1.3 Â 10 À7 s À1 with 0.2 wt% H 2 O added. Healing experiments were carried out on deformed samples at T = 200-500°C, P c = 500 MPa, for 4 h to 14 days under hydrostatic and nonhydrostatic conditions. The grain size distributions (GSD) of the deformed samples were quantified using the D > value (slope of log(frequency) -log(radius) of the GSD) for quartz and feldspar fault gouge. Healing causes a decrease in the D > value from >2.0 to $1.5. The time dependence of the D > decrease is described by a hydrostatic healing law of the form DD = D > (t) À D f = A Á e (ÀlÁt) . The results of the laboratory experiments were compared to three natural fault systems, (1) Nojima Fault Zone (Japan), (2) fault zones in the Black Forest (Germany), and (3) Orobic Thrust (Italian Alps). Natural and experimental gouges have similar D > values. Healing is only observed in monomineralic aggregates; polymineralic (i.e., mixed) fault gouges retain their high D > value after extended healing times because grain growth is inhibited. Healing under nonhydrostatic conditions is more rapid than hydrostatic healing. The low strain rates, which were measured during nonhydrostatic healing, are temperature-dependent and suggest that diffusive mass transfer processes take place during deformation. Thus, fault rocks at upper to midcrustal depth may deform by combined cataclasis and diffusive mass transfer.

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“…This suggests that the depth of 8 km is probably the shallow limitation of the pseudotachylite formation (Figure 10c). Boullier et al [2001] mentioned that the pseudotachylite layers were formed at around 15‐km depths on their fluid inclusion study, although they mentioned in their recent paper that the temperature might be slightly overestimated [ Boullier et al , 2004]. Temperature at the depth would be around 350°C, on the basis of the geothermal gradient of 23°C/km [ Kitajima et al , 2001].…”

Section: Discussionmentioning

confidence: 99%

“…In fact, the damage zone in stage II shear zone is extremely thick (Figure 10b), which resulted from the fracturing of weak, overpressurized fault zone at the middle depth of the crust. Although Gratier et al [2003] mentioned that pressure solution is the main mechanism of dissolution‐precipitation reactions for crack sealing, minor evidence of pressure solution was detected at the Nojima Fault zone [ Boullier et al , 2004], and the crack‐sealing mineral for shear zone in middle depth is zeolite. However, mass reduction from fault core and precipitation of zeolites in damaged zone is evident from the results of chemical isocon analysis (Figure 9) especially in stage II shear zones, which suggests that the shear zones were activated under fluid‐saturated, open‐system conditions.…”

Section: Discussionmentioning

confidence: 99%

Architectural evolution of the Nojima fault and identification of the activated slip layer by Kobe earthquake

Tanaka¹,

Omura²,

Matsuda³

et al. 2007

J. Geophys. Res.

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Evolutionary history of Nojima Fault zone is clarified by comprehensive examinations of petrological, geophysical, and geochemical characterizations on a fault zone in deep‐drilled core penetrating the Nojima Fault. On the basis of the results, we reconstruct a whole depth profile of the architecture of the Nojima Fault and identify the primal slip layer activated by 1995 Kobe earthquake. The deepest part (8‐ to 12‐km depth) of the fault zone is composed of thin slip layers of pseudotachylite (5 to 10 mm thick each, 10 cm in total). Middle depth (4‐ to 8‐km depth) of the fault zone is composed of fault core (6 to 10 m thick), surrounded by thick (100 m thick) damage zone, characterized by zeolite precipitation. The shallow part of the fault zone (1‐ to 4‐km depth) is composed of distributed narrow shear zones, which are characterized by combination of thin (0.5 cm thick each, 10 cm in total) ultracataclasite layers at the core of shear zones, surrounded by thicker (1 to 3 m thick) damage zones associated with carbonate precipitation. An extremely thin ultracataclasite layer (7 mm thick), activated by the 1995 Kobe earthquake, is clearly identified from numerous past slip layers, overprinting one of the shear zones, as evidenced by conspicuous geological and geophysical anomalies. The Nojima Fault zone was 10 to 100 times thicker at middle depth than that of shallower and deeper depths. The thickening would be explained as a combination of physical and chemical effects as follows. (1) Thickening of “fault core” at middle depth would be attributed to normal stress dependence on thickness of the shear zone and (2) an extreme thickening of “damage zone” in middle depth of the crust would result from the weakening of the fault zone due to super hydrostatic fluid pressure at middle depths. The high fluid pressure would result from faster sealing with low‐temperature carbonate at the shallower fault zone.

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Structural evolution of the Nojima fault (Awaji Island, Japan) revisited from the GSJ drill hole at Hirabayashi

Cited by 19 publications

References 25 publications

Microscale anatomy of the 1999 Chi‐Chi earthquake fault zone

Microscale anatomy of the 1999 Chi‐Chi earthquake fault zone

Healing microstructures of experimental and natural fault gouge

Architectural evolution of the Nojima fault and identification of the activated slip layer by Kobe earthquake

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