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

Ho Sim,Seongsik Hong,Sung-Ja Choi,Yungoo Song

doi:10.3390/min10110994

Abstract

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.

Highlights

Research on faults provides information on the ground stability of an area and important basic data for estimating the tectonic environment at the time of fault activation [1]
This study presented a large amount of data that can assess various types of shape preferred orientation (SPO) data that may affect the interpretation of fault motion
The SPO analysis was performed on outcrops of the Yangsan and Ulsan fault zones, which are the largest faults in the southeastern Korean Peninsula

Summary

Introduction

Research on faults provides information on the ground stability of an area and important basic data for estimating the tectonic environment at the time of fault activation [1]. Lattice preferred orientation (LPO) analysis of clay minerals using X-rays and anisotropy of magnetic susceptibility (AMS) analysis using the magnetic properties of minerals [6,7,8,9,10] are good methods for studying fault activation by investigating shear fabrics representative of incohesive fault rock. These methods cannot target all minerals, and more evidence is required for interpreting fault gouges.

Methods

Results

Discussion

Conclusion