Econ. Environ. Geol. 2023; 56(3): 293-300

Published online June 30, 2023

https://doi.org/10.9719/EEG.2023.56.3.293

© THE KOREAN SOCIETY OF ECONOMIC AND ENVIRONMENTAL GEOLOGY

The Shape Preferred Orientation (SPO) Analysis in Estimation of Fault Activity Study

Ho Sim1, Yungoo Song1,*, Changyun Park2, Jaewon Seo1

1Department of Earth System Sciences, Yonsei University, Seoul 120-749, Korea
2Department of Geology, Kyungpook National University, Daegu 702-701, Korea

Correspondence to : *yungoo@yonsei.ac.kr

Received: April 4, 2023; Revised: May 10, 2023; Accepted: May 11, 2023

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided original work is properly cited.

Abstract

The Shape Preferred Orientation (SPO) method has been used to analyze the orientation of fault motion, which is utilized as basic data for fault kinematics studies. The rigid grains, which as quartz, feldspar, and rock fragments, in the fault gouge are arranged in the P-shear direction through rigid body rotation by a given shear stress. Using this characteristic, the fault motion can be estimated from the SPO inversely. Recently, a method for securing precision and reliability by measuring 3D-SPO using X-ray CT images and examining the shape of a large number of particles in a short time has been developed. As a result, the SPO method analyzes the orientation of thousands to tens of thousands of particles at high speed, suggests the direction of fault motion, and provides easy accessibility and reliable data. In addition, the shape information and orientation distribution data of particles, which are by-products obtained in the SPO analysis process, are expected to be used as basic data for conducting various studies such as the local deformation of fault rocks and the fault generation mechanism.

Keywords Shape Preferred Orientation (SPO), fault gouge, X-ray CT, estimation of fault activation, rigid body rotation

단층 활동 추적 연구에서의 Shape Preferred Orientation (SPO) 분석법

심호1 · 송윤구1,* · 박창윤2 · 서재원1

1연세대학교 지구시스템과학과
2경북대학교 지질학과

요 약

Shape Preferred Orientation (SPO) 분석법은 단층의 운동학적 연구에 기초자료로 사용되는 단층면 운동 방향 분석을 위해 사용할 수 있는 방법으로 이용되어왔다. 단층비지 내 석영, 장석 등의 암편들로 이루어진 강성체들은 주어진 전단력에 의해 강성체 회전을 통해 P-전단 방향으로 배열되며, 이 특성을 이용해 역으로 SPO로부터 단층 운동 방향을 추정할 수 있다. 최근 X-선 CT영상을 활용해 3D-SPO를 측정하여 빠른시간 내에 다수의 입자들의 형태를 조사함으로서 정밀도와 신뢰성을 확보하는 방법이 개발되었다. 이로서 SPO 분석법은 수천~수만개 이상의 입자들의 방향성을 빠른 속도로 분석하여 단층 운동 방향을 제시하며 용이한 접근성과 신뢰도 높은 데이터를 제공한다. 더불어 SPO 분석과정에서 획득되는 부산물인 입자들의 형태학적 정보와 방향성 분포 데이터는 단층 활동 당시 일어난 단층암의 국부적 변형, 단층 발생 메커니즘과 같은 다양한 연구를 진행할 수 있는 기초데이터로서 활용 할 수 있을 것으로 기대된다.

주요어 Shape Preferred Orientation (SPO), 단층비지, X-선 CT, 단층 활동 추적, 강성체 회전

Article

Review

Econ. Environ. Geol. 2023; 56(3): 293-300

Published online June 30, 2023 https://doi.org/10.9719/EEG.2023.56.3.293

Copyright © THE KOREAN SOCIETY OF ECONOMIC AND ENVIRONMENTAL GEOLOGY.

The Shape Preferred Orientation (SPO) Analysis in Estimation of Fault Activity Study

Ho Sim1, Yungoo Song1,*, Changyun Park2, Jaewon Seo1

1Department of Earth System Sciences, Yonsei University, Seoul 120-749, Korea
2Department of Geology, Kyungpook National University, Daegu 702-701, Korea

Correspondence to:*yungoo@yonsei.ac.kr

Received: April 4, 2023; Revised: May 10, 2023; Accepted: May 11, 2023

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided original work is properly cited.

Abstract

The Shape Preferred Orientation (SPO) method has been used to analyze the orientation of fault motion, which is utilized as basic data for fault kinematics studies. The rigid grains, which as quartz, feldspar, and rock fragments, in the fault gouge are arranged in the P-shear direction through rigid body rotation by a given shear stress. Using this characteristic, the fault motion can be estimated from the SPO inversely. Recently, a method for securing precision and reliability by measuring 3D-SPO using X-ray CT images and examining the shape of a large number of particles in a short time has been developed. As a result, the SPO method analyzes the orientation of thousands to tens of thousands of particles at high speed, suggests the direction of fault motion, and provides easy accessibility and reliable data. In addition, the shape information and orientation distribution data of particles, which are by-products obtained in the SPO analysis process, are expected to be used as basic data for conducting various studies such as the local deformation of fault rocks and the fault generation mechanism.

Keywords Shape Preferred Orientation (SPO), fault gouge, X-ray CT, estimation of fault activation, rigid body rotation

단층 활동 추적 연구에서의 Shape Preferred Orientation (SPO) 분석법

심호1 · 송윤구1,* · 박창윤2 · 서재원1

1연세대학교 지구시스템과학과
2경북대학교 지질학과

Received: April 4, 2023; Revised: May 10, 2023; Accepted: May 11, 2023

요 약

Shape Preferred Orientation (SPO) 분석법은 단층의 운동학적 연구에 기초자료로 사용되는 단층면 운동 방향 분석을 위해 사용할 수 있는 방법으로 이용되어왔다. 단층비지 내 석영, 장석 등의 암편들로 이루어진 강성체들은 주어진 전단력에 의해 강성체 회전을 통해 P-전단 방향으로 배열되며, 이 특성을 이용해 역으로 SPO로부터 단층 운동 방향을 추정할 수 있다. 최근 X-선 CT영상을 활용해 3D-SPO를 측정하여 빠른시간 내에 다수의 입자들의 형태를 조사함으로서 정밀도와 신뢰성을 확보하는 방법이 개발되었다. 이로서 SPO 분석법은 수천~수만개 이상의 입자들의 방향성을 빠른 속도로 분석하여 단층 운동 방향을 제시하며 용이한 접근성과 신뢰도 높은 데이터를 제공한다. 더불어 SPO 분석과정에서 획득되는 부산물인 입자들의 형태학적 정보와 방향성 분포 데이터는 단층 활동 당시 일어난 단층암의 국부적 변형, 단층 발생 메커니즘과 같은 다양한 연구를 진행할 수 있는 기초데이터로서 활용 할 수 있을 것으로 기대된다.

주요어 Shape Preferred Orientation (SPO), 단층비지, X-선 CT, 단층 활동 추적, 강성체 회전

    Fig 1.

    Figure 1.The graph showing the circularity of particle rotation due to the continuously given shear strain. The result of analyzing each particle starting with different φi values and R=3, and the rotation result of the strain ellipse in the direction of the major axis are shown together (modified from Marques and Coelho., 2003). φ: The angle of rotation; R: Particle’s aspect ratio (=a/b); Sr: The rates of pure and simple shear components.
    Economic and Environmental Geology 2023; 56: 293-300https://doi.org/10.9719/EEG.2023.56.3.293

    Fig 2.

    Figure 2.Development history of SPO analysing method. (a) SPO of 2400 quartz measured from Takaka Hill quartzite and the orientation of c-axes given principle compressive stress for aspect ratio are shown. (b) The orientation of major axis is aligned differently according to the aspect ratio of the grain. (c), (d) The rose diagram shows the direction of the 2D-SPO in samples taken from the fault gouge. (e, f) The results of measuring 3D-SPO of samples taken from the San Andreas Fault Zone using X-CT are shown on lower-hemisphere equal area projections. (g, h) The results of measuring the 3D-SPO of a fault gouge sample from Yangsan fault for thousands of particles using synchrotron X-CT are shown in lower-hemisphere equal area projections with a result interpreted using a focal mechanism solution. (Modified from Shelley, 1995; Cladouhos, 1999; Sills, 2010; Sim et al., 2020a, 2020b).
    Economic and Environmental Geology 2023; 56: 293-300https://doi.org/10.9719/EEG.2023.56.3.293

    Fig 3.

    Figure 3.A schematic diagram showing the process of estimating the fault motion from the major axis direction of the rigid grains included in the core sample taken from the fault gouge. (a) A schematic diagram showing the core sample taken from the fault gouge and the separation of direction vectors according to the fault motion direction. (b) The orientation of grains included in the core sample is measured on the X-CT image. (c) Direction of fault motion (Vfm) and rake values are estimated through the grain SPO and plotted on a stereo-net (Modified from Sim et al., 2020b). Vss: vector of strike-slip; Vds: vector of dip-slip; Vfm: vector of fault motion; and VSPO: vector of densest point of SPO.
    Economic and Environmental Geology 2023; 56: 293-300https://doi.org/10.9719/EEG.2023.56.3.293

    Fig 4.

    Figure 4.The results of measuring the 3D-SPO of a fault gouge sample are shown in lower-hemisphere equal area projections. (a) The SPO analysis results of each representative sample with different orientation distributions of three axes are shown. The distribution of major/middle/minor axes are colored by red, blue, green, respectively. (b) the SPO analysis results according to the aspect ratio value are shown (Modified from Sim et al., 2020a, 2020b). Vc: the densest orientation vector of c axes; SDI: SPO Distribution Index.
    Economic and Environmental Geology 2023; 56: 293-300https://doi.org/10.9719/EEG.2023.56.3.293
    KSEEG
    Feb 29, 2024 Vol.57 No.1, pp. 1~91

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