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

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.

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

“…(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 fromShelley, 1995;Cladouhos, 1999;Sills, 2010;Sim et al, 2020aSim et al, , 2020b.…”

“…(b) The orientation of grains included in the core sample is measured on the X-CT image. (c) Direction of fault motion (V fm ) and rake values are estimated through the grain SPO and plotted on a stereo-net (Modified fromSim et al, 2020b). V ss : vector of strike-slip; Vds: vector of dip-slip; V fm : vector of fault motion; and V SPO : vector of densest point of SPO.…”

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

“…This method is optimized for estimating the orientation of the silt-sized rigid grains in fault gouge, which indicates P-shear direction in a fault system. Sim et al [5] successfully deduced fault motion sense and quantified the fault movement for the largest fault zones in the southeastern part of the Korean Peninsula. In this study, the authors provided information about fault motion by statistically presenting shape and orientation information for tens of thousands of grains.…”