Measurement of 3D-Shape Preferred Orientation (SPO) Using Synchrotron μ-CT: Applications for Estimation of Fault Motion Sense in a Fault Gouge

Sim, Ho; Song, Yungoo; Kim, Jaehun; Yang, Eomzi; Yun, Tae Sup; Lim, Jae Hong

doi:10.3390/min10060528

Cited by 4 publications

(11 citation statements)

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“…In addition, as a result of measuring the SPO of the fault gouge and breccia quartz grains, it was confirmed that this alignment was also exhibited in natural fault rock samples [11]. Recently, the fault motion was estimated by measuring the SPO of the major axis of the grain in 3D through a CT image of the fault gouge [13,14]. According to previous studies, the densest points of the SPO are aligned in the P-shear direction; therefore, the fault motion direction can be estimated from the SPO.…”

Section: Orientation Of Major Axismentioning

confidence: 57%

“…The method of measuring 3D-SPO of the collected sample was based on Sim et al (2020) [14]. Octopus 8.9 software (XRE, Gent, Belgium) was used for image reconstruction and all image-related processes were performed using Amira 6.5 (Thermo Fisher Scientific, Hillsboro, OR, USA) and MATLAB (MathWorks, Natick, MA, USA).…”

Section: Shape Preferred Orientation Measurement Methodsmentioning

confidence: 99%

“…The acquired information was plotted on an equal-area stereonet and the SPO distribution index (SDI) was calculated using the information of the major, intermediate, and minor axes. The SDI indicates how the SPO data are scattered from the reference point, which indicates the most frequent orientation [14]. The SDI can be expressed as follows:…”

Section: Shape Preferred Orientation Measurement Methodsmentioning

confidence: 99%

“…To solve this problem, the three-dimensional (3D)-SPO method was recently developed. According to a previous study that measured 3D-SPO, fault motion sense can be inferred by analyzing the shape characteristics of rigid grains and the orientation of the major axis of the grains evaluated through grain rotation [13,14]. Compared with past studies on 2D planes, reliability and data accuracy can be improved by using the large amount of data collected via micro-computed tomography (µ-CT).…”

Section: Introductionmentioning

confidence: 99%

“…However, the SPO method has not yet been applied to various fault rocks appearing in large-scale faults. Additionally, even if there are other possibilities for interpreting SPO results, detailed studies investigating this aspect are lacking [14]. In particular, previous studies have discussed only the orientation of the major axis.…”

Section: Introductionmentioning

confidence: 99%

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3D Fabric Analysis in Fault Rock Using Synchrotron μ-CT: A Statistical Approach to SPO (Shape Preferred Orientation) for Estimation of Fault Motion

et al. 2020

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This study provides information about fault motion by statistically presenting shape and orientation information for tens of thousands of grains. The recently developed shape preferred orientation (SPO) measurement method using synchrotron micro-computed tomography was used. In addition, various factors that were not considered in previous SPO analysis were analyzed in-depth. The study area included the Yangsan and Ulsan fault zones, which are the largest fault zones in the southeastern part of the Korean Peninsula. Samples were collected from five outcrops in two regions. According to the field observation results, the samples in the area were largely divided into fault gouge and cataclasite, and as a result of SPO analysis, we succeeded in restoring the three-dimensional fault motion direction for each outcrop and identified the fault type. In addition, the analysis results of the fault gouge and cataclasite samples collected from the thin fault zone were interpreted using the focal mechanism solution. As a result, the statistical SPO analysis approach supplements the shortcomings of previous research methods on two-dimensional planes and can quantitatively infer the three-dimensional fault motion for various fault rock samples in the same sequence, thus, presenting useful evidence for structural analysis.

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Section: Orientation Of Major Axismentioning

confidence: 57%

Section: Shape Preferred Orientation Measurement Methodsmentioning

confidence: 99%

Section: Shape Preferred Orientation Measurement Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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3D Fabric Analysis in Fault Rock Using Synchrotron μ-CT: A Statistical Approach to SPO (Shape Preferred Orientation) for Estimation of Fault Motion

et al. 2020

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The Magnetic Fabric of Gouge Mimics the Coseismic Focal Mechanism of the Chi‐Chi Earthquake (1999, Mw 7.6)

Chou

Aubourg

Yeh

et al. 2020

Geophysical Research Letters

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We present a magnetic fabric investigation of small oriented rock fragments from gouges and wall rocks from the Chelungpu fault (Taiwan), where the Chi-Chi earthquake occurred (M w 7.6, 1999). Samples are obtained from surface outcrops and at a depth of~1 km, including the 3-mm-thick Chi-Chi principal slip zone. Wall rocks at depth show magnetic foliation roughly parallel to bedding, whereas they are oblique at the surface. Within the gouges, the mean shape of magnetic ellipsoid is oblate, and the degree of anisotropy is up to 12%. The magnetic foliation diverges of~40°from the fault plane, compatible with a simple shear westward. The magnetic lineation is oblique, resulting probably from coseismic and interseismic records. The reconstructed focal mechanism from the magnetic fabric closely matches the focal mechanism solutions for the Chi-Chi earthquake. Our work demonstrates that magnetic fabric of gouge fragments can bring valuable kinematic information on modern earthquakes. Plain Language Summary Fault gouges often provide important and valuable information that can help to understand the fault mechanisms and to assess the seismic hazard, but to get access to the shape preferred orientation of micrometric minerals is generally a complex, time consuming and expensive procedure. In this study, we show that the anisotropy of magnetic susceptibility, which is a fast and nondestructive technique, can be a proxy of the structural fabric of historical gouges. This technique has already been previously applied to gouge zones, but this is the first time that it is used in the gouge from one of the best documented historical large seismic events: the 1999 Chi-Chi earthquake (M w 7.6) along the Chelungpu fault (Taiwan). Samples within and around this fault were obtained from fresh surface outcrop and 1-km-deep borehole (Hole B, Taiwan Chelungpu-fault Drilling Project). The 1-km-deep gouge hosts the 3-mm-thick principal slip zone of the Chi-Chi earthquake. The results show that the reconstructed focal mechanism based on the magnetic fabric geometry matches closely the focal mechanism solutions for the Chi-Chi earthquake estimated by several previous studies.

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Editorial for Special Issue “Microtexture Characterization of Rocks and Minerals”

Song

2021

Minerals

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Measurement of 3D-Shape Preferred Orientation (SPO) Using Synchrotron μ-CT: Applications for Estimation of Fault Motion Sense in a Fault Gouge

Cited by 4 publications

References 32 publications

3D Fabric Analysis in Fault Rock Using Synchrotron μ-CT: A Statistical Approach to SPO (Shape Preferred Orientation) for Estimation of Fault Motion

3D Fabric Analysis in Fault Rock Using Synchrotron μ-CT: A Statistical Approach to SPO (Shape Preferred Orientation) for Estimation of Fault Motion

The Magnetic Fabric of Gouge Mimics the Coseismic Focal Mechanism of the Chi‐Chi Earthquake (1999, Mw 7.6)

Editorial for Special Issue “Microtexture Characterization of Rocks and Minerals”

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