On the Curved Striations of Nojima Seismic Fault Engraved at the 1995 Hyogoken-Nambu Earthquake, Japan

Otsuki, Kenshiro; Minagawa, Jun; Aono, Masao; Ohtake, Masakazu

doi:10.4294/zisin1948.49.4_451

Cited by 15 publications

(12 citation statements)

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“…The direction of fault motion during the rupture of the 2011 Iwaki earthquake, therefore, shifted from a normal faulting with a left-lateral component to that with a right-lateral component. Curved slickenlines from intraplate earthquakes have been reported in other areas (e.g., the 1995 Hyogo-ken Nanbu (Kobe) earthquake; Otsuki et al, 1997).…”

mentioning

confidence: 73%

Slickenlines on fault scarps caused by an earthquake in Iwaki-city (Fukushima Prefecture, Japan) on 11 April 2011

Otsubo

Shigematsu

Takahashi

et al. 2012

Jour. Geol. Soc. Japan

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mentioning

confidence: 73%

Slickenlines on fault scarps caused by an earthquake in Iwaki-city (Fukushima Prefecture, Japan) on 11 April 2011

Otsubo

Shigematsu

Takahashi

et al. 2012

Jour. Geol. Soc. Japan

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“…The layer of soft clay is only few cm thick, and separates alternating units of laminated fault rock and granite cataclasite to the southeast from fine sandstone of the Osaka Group to the northwest. Detailed observations suggest that the seismic slip of the 1995 Hyogo‐ken Nanbu earthquake occurred only in this clay layer [ Otsuki et al , 1997]. …”

Section: Geologic Setting and Occurrence Of The Fault Rockmentioning

confidence: 99%

Fluidization and melting of fault gouge during seismic slip: Identification in the Nojima fault zone and implications for focal earthquake mechanisms

2003

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The record of physical processes that occur during seismic slip events is well preserved in fault rocks from the active Nojima fault in Japan. The fault rocks formed at about 3 km depth, and comprise thin alternating layers of very fine gouge and pseudotachylyte derived from granite. Each layer is thinner than a few millimeters, and corresponds to one seismic slip event. The very thin slip zone width suggests that some mechanisms of slip weakening operated, and our studies of the fault rocks suggest that fluidization and melting of gouge were particularly important. Fluidized and nonfluidized gouges were distinguished using the detection probability of fragmented counterparts method. It is known from granular material science that the phase transition from a grain friction regime to fluidization of granular materials can occur only by a very small decrease in volume fraction of solid grains. Once fluidization occurs, the frictional resistance decreases abruptly to nearly zero even before thermal pressurization reaches its extreme state. When fault gouge is melted, frictional resistance is governed by the viscosity of melt which depends mainly on temperature, chemical composition, H2O concentration and the volume fraction of unmelted grains. For each pseudotachylyte layer, we estimated the temperature of melt using various temperature indices, and measured volume fraction of unmelted grains. We synthesized these data to reconstruct the change in viscosity during seismic slip events. The melt viscosity is very high (107–9 Pas) during initial melting due to the combined effect of low temperature (750°–800°C) and large volume fraction of solid grains. Thus seismic slip is inevitably restrained instantaneously. Once this mechanical barrier is overcome, the viscosity reduces continuously and dramatically as slip increases. At 1000°C, the viscosity reduces to 104Pas and eventually to 10Pas at 1280°C. Thus stress drops almost completely and rupturing tends to run away.

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“…Great earthquake can leave curved fault striae such as those on the fault plane of the 1995 Hyogo-ken Nanbu (Kobe) earthquake (Yosida et al, 1996;Otsuki et al, 1997). In those cases, coseismic slip direction changes spatially and temporarily with the change of local shear traction across the fault plane (Guatteri and Spudich, 1998), resulting in heterogeneous fault-slip data.…”

Section: Introductionmentioning

confidence: 99%

The multiple inverse method: a new technique to separate stresses from heterogeneous fault-slip data

Yamaji

2000

Journal of Structural Geology

267

162

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A new inverse technique is presented here to separate stresses from heterogeneous fault-slip data without a priori information on the stresses nor on the classification of faults according to the stresses. Four parameters are determined by the inversion: one for the shape of stress ellipsoid and three for the direction of stress axes. Accordingly, the inversion is equivalent to the projection of fault-slip data to a point in four-dimensional parameter space. The data are divided into k-element subsets to which inverse technique is applied, where k = 4 or 5 is the optimal choice for the stability of solutions and for the reduction of computation. Significant solutions are identified as the clusters in the parameter space. The technique is demonstrated first by simulated fault-slip data. And, as an example, field data obtained from Miocene fore-arc sediments in western Japan were processed by the method.

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On the Curved Striations of Nojima Seismic Fault Engraved at the 1995 Hyogoken-Nambu Earthquake, Japan

Cited by 15 publications

References 0 publications

Slickenlines on fault scarps caused by an earthquake in Iwaki-city (Fukushima Prefecture, Japan) on 11 April 2011

Slickenlines on fault scarps caused by an earthquake in Iwaki-city (Fukushima Prefecture, Japan) on 11 April 2011

Fluidization and melting of fault gouge during seismic slip: Identification in the Nojima fault zone and implications for focal earthquake mechanisms

The multiple inverse method: a new technique to separate stresses from heterogeneous fault-slip data

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