We study the geomechanical stability of faults in southeastern Korea that have been active during the Quaternary (mostly Pleistocene), to investigate whether these faults can still be considered active today. We compile fault plane data and slip orientations for 40 Quaternary faults in southeastern Korea distributed along the two major fault systems, Yangsan Fault (group 1) and Ulsan Fault (group 2), and in the younger block to the east of the Ulsan Fault (group 3). Our aim is to determine the representative tectonic stress states in the Quaternary and in the present day, and to compare the slip susceptibility of these faults under the stress fields of these two periods. We estimate Quaternary stress from inversion of Quaternary fault data, and present-day stress from inversion of contemporary earthquake mechanisms. Both stress fields exhibit a maximum principal stress axis that is sub-horizontal and trends ENE-WSW, but the intermediate and minimum principal stress axes are switched, suggesting a change in stress regime from reverse-faulting during the Quaternary to strike-slip-faulting in the present day. We demonstrate that this change in stress regime is due to a marked reduction in the magnitude of horizontal tectonic stress from the Quaternary to the present day. We assess the slip susceptibility of the faults under the Quaternary and present-day stress fields using two indices: slip tendency and fault instability. This analysis shows an increase in slip susceptibility for most of group 1 faults and some of group 3 faults. Some of these faults exhibit a slip susceptibility comparable to the average obtained for contemporary earthquake focal planes, suggesting that these faults can be considered active in the present day.

我们研究了第四纪（主要是更新世）期间活跃的韩国东南部断层的地质力学稳定性，以调查这些断层今天是否仍被认为是活跃的。我们收集了分布在韩国东南部的40个第四纪断层的断层平面数据和滑动方向，这些断层分布在两个主要断层系统上，即良山断层（第1组）和蔚山断层（第2组），以及蔚山断层以东的较年轻块体（第3组）。我们的目的是确定第四纪和今天的典型构造应力状态，并比较这两个断层在这两个时期的应力场下的滑动敏感性。我们根据第四纪断层数据的反演来估计第四纪应力，而根据当代地震机制的反演来估计当前应力。这两个应力场都显示了一个最大的次应力主应力轴，并处于ENE-WSW趋势，但是中间和最小的主应力轴发生了切换，这表明应力机制从第四纪的逆断层转变为走滑断层。在今天。我们证明了这种应力状态的变化是由于从第四纪到今天水平构造应力的大小显着减小。我们使用两个指数：滑动趋势和断层不稳定性来评估第四纪和当前应力场下断层的滑动敏感性。该分析表明，对于第1组大多数断层和第3组某些断层，滑动敏感性增加。其中一些断层的滑动敏感性与当代地震震源的平均值相当，