Spatial variation of shear‐wave splitting across an active fault and its implication for stress accumulation mechanism of inland earthquakes: The Atotsugawa fault case

Mizuno, Takashi; Ito, Hisao; Kuwahara, Yasuto; Imanishi, Kazutoshi; Takeda, Tetsuya

doi:10.1029/2005gl023875

Cited by 29 publications

(52 citation statements)

References 15 publications

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“…5.1 Comparison with previous studies on focal mechanisms Stress field in the northern Hida region including the Atotsugawa fault zone has been investigated by Mikumo et al (1985Mikumo et al ( , 1988, Koizumi et al (1993), and Wada et al (2003) on the basis of focal mechanism data. Mikumo et al (1985Mikumo et al ( , 1988 showed that focal mechanisms along and westward extension of Atotsugawa fault are mostly strikeslip with ENE-WSW trending nodal planes.…”

Section: Discussionmentioning

confidence: 89%

“…Mikumo et al (1985Mikumo et al ( , 1988 showed that focal mechanisms along and westward extension of Atotsugawa fault are mostly strikeslip with ENE-WSW trending nodal planes. Outside the Atotsugawa fault zone, they found reverse faulting events in the northwestern part and normal faulting events in the northern part.…”

Section: Discussionmentioning

confidence: 99%

“…Along the Atotsugawa fault system, the P-axis is oriented WNW-ESE, which is consistent with the regional trend in the Chubu region. Several researchers (Mikumo et al, 1988;Koizumi et al, 1993) pointed out a systematic deviation of P-and T -axes in the Hida Mountain ranges from the regional trend. In addition to many strike-slip type focal mechanisms in the Atotsugawa area, some events particularly in the southwestern part of fault exhibit dip-slip mechanisms having inconsistent P-axes with the fault movement.…”

Section: Introductionmentioning

confidence: 99%

“…Generally seismicity along active faults in Japan decreases to very low level long after large earthquakes, however, the present seismicity along the Atotsugawa fault system is extraordinarily high even though more than 150 years have passed from the Hietsu earthquake. Seismicity in the Atotsugawa fault area has been investigated by many researchers (Mikumo et al, 1985(Mikumo et al, , 1988Wada and Ito, 1995;Wada et al, 2001;Ito and Wada, 2002;Ito et al, 2003). Earthquakes along the Atotsugawa and the Mozumi-Sukenobu faults form narrow vertical planes with a thickness of less than 2 km.…”

Section: Introductionmentioning

confidence: 99%

“…Earthquake focal mechanisms in the northwest Chubu (Hida) region have been studied by Mikumo et al (1985Mikumo et al ( , 1988, Koizumi et al (1993), Wada and Ito (1995), and Wada et al (2001Wada et al ( , 2003. Along the Atotsugawa fault system, the P-axis is oriented WNW-ESE, which is consistent with the regional trend in the Chubu region.…”

Section: Introductionmentioning

confidence: 99%

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Focal mechanisms and stress field in the Atotsugawa fault area, central Honshu, Japan

2010

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We have determined 151 high quality focal mechanism solutions for earthquakes that occurred between January 2005 and December 2006 in and around the Atotsugawa fault area in central Honshu, Japan. We used P-wave first motion polarity data observed by a dense temporary seismic observation conducted in the area by the Japanese University Group. The types of obtained focal mechanism solutions are predominantly strike-slip, however, some earthquakes exhibit reverse-and normal-fault type focal mechanisms. Without regard to faulting type, the averaged directions of compressional (P) and extensional (T ) axes are rather uniform, N70 • W and N16 • E, respectively. We found that not a small number of normal-fault type earthquakes occurred in a small cluster near the central part of Atotsugawa fault, and in a very short period from the end of March to the beginning of April in 2005. In order to estimate stress field around the fault, we applied a stress tensor inversion method to the focal mechanism solutions. Both the maximum principal stress (σ 1 ) and the minimum principal stress (σ 3 ) axes are almost horizontal and trend N72 • W to N77 • W and N14 • E to N20 • E, respectively. The direction of σ 1 and the fault trace form an angle of 43 • -48 • . It is clear that the σ 1 axis is neither perpendicular nor parallel to the Atotsugawa fault, indicating strong coupling of fault. The stress tensor inversion also suggests local extensional stress field at a deep (>8 km) central part of Atotsugawa fault. We present a hypothesis that the extensional stress is caused locally in a transition zone from the fluid-rich aseismic creep zone to the seismogenic zone that is interpreted as an asperity ruptured by the 1858 Hietsu Earthquake (M = 7.0).

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Section: Discussionmentioning

confidence: 89%

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Focal mechanisms and stress field in the Atotsugawa fault area, central Honshu, Japan

2010

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Stress‐induced spatiotemporal variations in anisotropic structures beneath Hakone volcano, Japan, detected by S wave splitting: A tool for volcanic activity monitoring

et al. 2014

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Hakone volcano, located at the northern tip of the Izu-Mariana volcanic arc, Japan, has a large caldera structure containing numerous volcanic hot springs. Earthquake swarms have occurred repeatedly within the caldera. The largest seismic swarm since the commencement of modern seismic observations (in 1968) occurred in 2001. We investigated the anisotropic structure of Hakone volcano based on S wave splitting analysis and found spatiotemporal changes in the splitting parameters accompanying the seismic swarm activity. Depth-dependent anisotropic structures are clearly observed. A highly anisotropic layer with a thickness of~1.5 km is located beneath the Koziri (KZR) and Kozukayama (KZY) stations. The anisotropic intensity in the region reaches a maximum of 6-7% at a depth of 1 km and decreases markedly to less than 1% at a depth of 2 km. The anisotropic intensity beneath Komagatake station (KOM) decreases gradually from a maximum of 6% at the surface to 0% at a depth of 5 km but is still greater than 2.5% at a depth of 3 km. At KZY, the anisotropic intensity along a travel path of which the back azimuth was the south decreased noticeably after the 2001 seismic swarm activity. During the swarm activity, tilt meters and GPS recorded the crustal deformation. The observed decrease in anisotropic intensity is presumed to be caused by the closing of microcracks by stress changes accompanying crustal deformation near the travel path.

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Elastic Anisotropy Reversal During Brittle Creep in Shale

Geng

Bonnelye

Chen

et al. 2017

Geophysical Research Letters

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We conducted two brittle creep experiments on shale samples under upper crustal conditions (confining pressure of 80 MPa at 26°C and 75°C). We deformed the samples to failure, with bedding oriented perpendicular to the maximum compressive stress direction, using the stress-stepping methodology. In both experiments, the failure stress was~64% higher than the short-term peak strength. Throughout each differential stress step, ultrasonic wave velocities initially decreased and then gradually increased with deformation/time. The magnitude of these variations depends both on the direction of measurement with respect to the bedding and the temperature, and it is largest for velocities measured parallel to the bedding and at high temperature. Elastic wave anisotropy was completely reversed at 75°C, following a limited amount of axial strain (~0.6%). Scanning electron microscope investigation confirmed evidence of a time-dependent pressure solution, localized compaction, crack sealing/healing, and mineral rotation. Our observations reveal that elastic anisotropy can evolve rapidly in both time and space, which has implications on the stress state and its rotation near fault zones. Recently, Bonnelye et al. (2017a, 2017b) studied the influence of bedding and stress on elastic wave anisotropy in "anisotropic" Tournemire shale samples deformed at constant strain rates. To our knowledge, only GENG ET AL.

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Spatial variation of shear‐wave splitting across an active fault and its implication for stress accumulation mechanism of inland earthquakes: The Atotsugawa fault case

Cited by 29 publications

References 15 publications

Focal mechanisms and stress field in the Atotsugawa fault area, central Honshu, Japan

Focal mechanisms and stress field in the Atotsugawa fault area, central Honshu, Japan

Stress‐induced spatiotemporal variations in anisotropic structures beneath Hakone volcano, Japan, detected by S wave splitting: A tool for volcanic activity monitoring

Elastic Anisotropy Reversal During Brittle Creep in Shale

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