Variability of Fault Damage Zone Width in Strike−Slip Faults: A Case Study from the Coast of Geoje Island, Korea

Fault damage zones are regions surrounding a fault core where secondary fractures are intensely developed due to distributed deformation. Previous studies on small-scale faults (consisting of one or two geometric segments) have predicted that the characteristics of the damage zone vary depending on the position along the fault. However, applying these models to large-scale fault zones is challenging due to the lack of continuous exposure and their inherent structural complexity.

This study aims to analyze the spatial variability of damage zone width in relation to fault geometry, focusing on medium-scale strike-slip faults (comprising three or more geometric segments), which offer a balance between structural complexity and observable continuity. The study area, Geoje Island, consists of hornfelsic Cretaceous lacustrine sedimentary rocks. The extensive wave-cut platforms along the coast provide excellent exposure for characterizing the geometry of the master fault and associated damage zones.

Fracture density (P₂₁) was systematically quantified across fault segments and boundaries using circular scanlines arranged along strike-perpendicular traverses. The width of the damage zone along each traverse scanlines was determined by analyzing the changes in fracture density relative to the distance from the Principal Displacement Zone (PDZ). The results indicate that the width of the damage zone is highly variable and exhibits significant asymmetry in certain sections. Specifically, in linking damage zones, a widespread distribution of damage is observed beyond the extensional overlap zones, contrasting with patterns typically seen in small-scale faults. Furthermore, strong asymmetry is prominent in regions where the fault strike changes. However, such widespread damage distribution and asymmetry are well consistent with the characteristics of tip damage zones observed in small-scale faults.

These observations indicate that geometric complexity at these locations contributed to arresting rupture propagation during reactivation. Although individual rupture mechanics are similar across scales, the cumulative effect of geometric barriers in medium-scale faults appears to dictate the spatial evolution of the damage zone.  These findings are expected to provide valuable insights for predicting and understanding the architectural evolution of large-scale fault zones.

 

This research was supported by a grant (2022-MOIS62-001(RS-2022-ND640011)) of National Disaster Risk Analysis and Management Technology in Earthquake funded by Ministry of Interior and Safety (MOIS, Korea).