Consideration of the Activity of a Fault Based on Detailed Structural Analysis of a Fault Fracture Zone

Aiyama, Kotaro; Tanaka, Shiro; Sasaki, Toshinori

doi:10.5110/jjseg.58.2

Cited by 7 publications

(6 citation statements)

References 6 publications

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“…S4f ). Aiyama et al (2017), observing the active Yamada fault in a granitic outcrop in central Japan, described layered gouge zones within the FFZ; whereas inactive minor faults in the same outcrop were in direct contact with cataclasite and not associated with gouge. At the active trace of the Nojima fault in central Japan, layers of gouge in granite have been explained by repetitive faulting at shallow crustal levels (Shigetomi and Lin 1999;Otsuki et al 2003).…”

Section: Detection and Assessment Of Slow Slip-rate Faultsmentioning

confidence: 99%

Surface rupture and characteristics of a fault associated with the 2011 and 2016 earthquakes in the southern Abukuma Mountains, northeastern Japan, triggered by the Tohoku-Oki earthquake

Komura

Aiyama

Nagata

et al. 2019

Earth Planets Space

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The 2011 Tohoku-Oki offshore subduction earthquake (M w 9.0) triggered many normal-type earthquakes inland in northeastern Japan. Among these were two very similar normal-faulting earthquakes in 2011 (M w 5.8) and 2016 (M w 5.9), which created surface ruptures along the newly named Mochiyama fault within the southern Abukuma Mountains, northeastern Japan, where no active faults had been previously mapped by interpretation of aerial photographs. We conducted field surveys in this area immediately after both earthquakes, and we performed trench excavations and observations of fault fracture zones after the 2016 event. These activities were complemented by an interferometric synthetic aperture radar analysis that mapped the areas of deformation and locations of surface discontinuities for both events. The combined results document the coseismic behavior of the Mochiyama fault during both events. Subtle tectonic geomorphic features associated with the fault were evident in a lidar digital elevation model of the area, and layered structures of gouge were documented in the field. These lines of evidence indicate repeated activity at shallow crustal levels and the possibility of Quaternary activity. In addition, our trench excavations revealed at least one faulting event before 2011. Our comparison of paleoseismic records on this and two other normal faults in the Abukuma Mountains suggests that great earthquakes in the Japan Trench supercycle of 500-700 years do not consistently trigger ruptures on these faults, and the case of 2011, in which the Tohoku-Oki megathrust earthquake triggered all three faults, is a rare occurrence.

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Section: Detection and Assessment Of Slow Slip-rate Faultsmentioning

confidence: 99%

Surface rupture and characteristics of a fault associated with the 2011 and 2016 earthquakes in the southern Abukuma Mountains, northeastern Japan, triggered by the Tohoku-Oki earthquake

Komura

Aiyama

Nagata

et al. 2019

Earth Planets Space

Self Cite

View full text Add to dashboard Cite

show abstract

“…Aiyama et al (2017) investigated the activity of this fault in the Mushu outcrop, and reported that the main fault plane, which has been active during the Quaternary, contains a fault gouge zone. Aiyama et al (2017) also characterized this fault gouge zone as a layered structure with ten fault gouge layers that are indicative of repetitive activity after smectite crystallization. Iwamori et al (2015) studied the activity of the Yamada Fault over the last ~200,000 years based on the faults that cut the sedimentary layer above the Mushu outcrop, and reported that the youngest fault activity occurred between 2,000 and 200 years B.P.…”

Section: Yamada Fault (Musyu Outcrop; Active Fault)mentioning

confidence: 99%

“…Hirono et al (2008) used X-ray CT to analyze the fault rocks generated during the 1999 Chi-Chi Earthquake; however, they were unable to report on the relationship between the CT number and fault rock density, owing to the beam hardening (BH) effect. Aiyama et al (2017) recently observed the internal structure of a fault fracture zone using medical X-ray CT, and reported that the CT image of the fault gouge zone was darker and less dense than that of the surrounding cataclasite. X-ray CT is generally conducted using either industrial-or medical-grade scanners.…”

Section: Introductionmentioning

confidence: 99%

Determination of the Youngest Active Domain in Major Fault Zones Using Medical X-ray Computed Tomography-derived Density Estimations

Iwamori

Takahashi

Asahi³

et al. 2021

Preprint

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Determination of the youngest active domains in fault zones that are not overlain by Quaternary sedimentary cover are critical for evaluating recent fault activity, determining the current local stress field, and mitigating the impacts of future earthquakes. Considering the exhumation of a fault zone, the youngest active domain in a fault zone is supposed to correspond to the activity at the minimum fault depth of a buried fault, such that the most vulnerable area, which possesses the lowest rock/protolith density ratio, is assumed to be indicative of this recent fault activity. However, it is difficult to measure the density of fault rocks and map the rock/protolith density ratio across a given fault zone. Here we utilize medical X-ray computed tomography (CT), a non-destructive technique for observing and analyzing materials, to investigate the fault characteristics of several fault zones and their surrounding regions in Japan, and attempt to determine the youngest active domain of a given fault zone based on its CT numbers, which are a function of the density and effective atomic number of the fault rock and protolith. We first investigate the density, void ratio, and effective atomic number of active and inactive fault rocks, and their respective protoliths. We then calculate the CT numbers after reducing the beam-hardening effects on the rock samples, and study the relationships among the CT number, density, and effective atomic number. We demonstrate that the density, effective atomic number, and CT number of the fault rock decrease as the youngest active zone is approached, such that the region with the lowest CT number and rock/protolith density ratio defines the youngest active domain of a given fault zone.

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“…The fault gouge zone is very soft and shows a dextral sense of shear. Aiyama et al (2017) investigated the activity of this fault in the Mushu outcrop and reported that the main fault plane, which has been active during the Quaternary, contains a fault gouge zone. Aiyama et al (2017) also characterized this fault gouge zone as a layered structure with ten fault gouge layers that are indicative of repetitive activity after smectite crystallization.…”

Section: Yamada Fault (Musyu Outcrop; Active Fault)mentioning

confidence: 99%

“…Hirono et al (2008) used X-ray CT to analyze the fault rocks generated during the 1999 Chi-Chi earthquake; however, they were unable to report on the relationship between the CT number and fault rock density, owing to the beam hardening (BH) effect. Aiyama et al (2017) recently observed the internal structure of a fault fracture zone using medical X-ray CT and reported that the CT image of the fault gouge zone was darker and less dense than that of the surrounding cataclasite.…”

Section: Introductionmentioning

confidence: 99%

Quantitative determination of the lowest density domain in major fault zones via medical X-ray computed tomography

Iwamori

Takahashi

Asahi³

et al. 2021

Prog Earth Planet Sci

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Determination of the youngest active domains in fault zones that are not overlain by Quaternary sedimentary cover is critical for evaluating recent fault activity, determining the current local stress field, and mitigating the impacts of future earthquakes. Considering the exhumation of a fault zone, the youngest active domain in a fault zone is supposed to correspond to the activity at the minimum fault depth of a buried fault, such that the most vulnerable area, which possesses the lowest rock/protolith density ratio, is assumed to be indicative of this recent fault activity. However, it is difficult to measure the density of fault rocks and map the rock/protolith density ratio across a given fault zone. Here, we utilize medical X-ray computed tomography (CT), a non-destructive technique for observing and analyzing materials, to investigate the fault characteristics of several fault zones and their surrounding regions in Japan, and attempt to determine the lowest density domain of a given fault zone based on its CT numbers, which are a function of the density and effective atomic number of the fault rock and protolith. We first investigate the density, void ratio, and effective atomic number of active and inactive fault rocks, and their respective protoliths. We then calculate the CT numbers after reducing the beam-hardening effects on the rock samples and study the relationships among the CT number, density, and effective atomic number. We demonstrate that the density, effective atomic number, and CT number of the fault rock decrease as the youngest active zone, identified by outcrop observation, are approached, such that the region with the lowest CT number and rock/protolith density ratio defines the lowest density domain of a given fault zone. We also discuss the relationship between the lowest density domain and the youngest active domain in major fault zones and investigate the points to be considered when the youngest active domain is identified from the lowest density domain determined by the CT number.

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Consideration of the Activity of a Fault Based on Detailed Structural Analysis of a Fault Fracture Zone

Cited by 7 publications

References 6 publications

Surface rupture and characteristics of a fault associated with the 2011 and 2016 earthquakes in the southern Abukuma Mountains, northeastern Japan, triggered by the Tohoku-Oki earthquake

Surface rupture and characteristics of a fault associated with the 2011 and 2016 earthquakes in the southern Abukuma Mountains, northeastern Japan, triggered by the Tohoku-Oki earthquake

Determination of the Youngest Active Domain in Major Fault Zones Using Medical X-ray Computed Tomography-derived Density Estimations

Quantitative determination of the lowest density domain in major fault zones via medical X-ray computed tomography

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