Quaternary surface ruptures of the inherited mature Yangsan Fault: implications for intraplate earthquakes in southeastern Korea

Abstract

Earthquake prediction in intraplate regions, such as the Korean Peninsula, is challenging due to the complexity of fault distributions. This study employed diverse methods and data sources to investigate Quaternary surface rupturing along the Yangsan Fault, aiming to understand its long-term earthquake behavior. Paleoseismic data from the Byeokgye section (7.6 km) of the Yangsan Fault are analyzed to provide insights into earthquake parameters (i.e., timing, displacement, and recurrence intervals) as well as structural patterns. Observations from five trench sites indicate at least six faulting events during the Quaternary, with the most recent surface rupturing occurring approximately 3000 years ago. These events resulted in a cumulative horizontal displacement of 76 m and a maximum estimated magnitude of Mw 6.7–7.1. The average slip rate of 0.13 ± 0.1 mm yr−1 suggests a quasi-periodic model with possible recurrence intervals exceeding 13 000 years. Structural patterns indicate the reactivation of a pre-existing fault core with top-to-the-west geometry, causing a dextral slip with a minor reverse component. This study underscores the several surface ruptures with large earthquakes along the inherited mature Yangsan Fault, since at least the Early Pleistocene, offering critical insights for seismic hazard and a broader understanding of intraplate earthquake dynamics, enhancing earthquake prediction efforts.