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Two groups of Quaternary faults occur in the southeastern Korean Peninsula. The first group is north‐northeast‐striking, high‐angle dextral strike–slip faults. The second group is north‐northeast‐striking, low‐angle reverse faults that represent the reactivation of the pre‐existing normal faults. Optically stimulated luminescence dating of Quaternary sediments cut by one of the reverse faults constrains the faulting age to post‐32 Ka. These faults seem to be capable of further slip under the current tectonic stress regime, as determined by recent earthquake events in northeast Asia. Therefore, the traditional concept that the southeastern Korean Peninsula is seismically stable should be reappraised.

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Crustal velocities within South Korea were estimated using GPS data and interpreted in terms of neotectonics. Twenty months of data for the seven GPS stations in South Korea were analyzed to estimate velocities relative to Taejon (DAEJ), a central region of South Korea. From the time series of horizontal position of each station, we estimated site velocities with an accuracy of 0.5 mm/year or better mostly. The relative velocities within the Korean peninsula are very small (∼1 mm/year), convertible to strain rates in the order of 0.01 ppm/yr. They indicate the Korean peninsula is likely to be tectonically more stationary than other countries in the East Asia, for example, Japan or Taiwan. The result of GPS analysis suggests a possibility that northwestward tectonic force due to the AM (Amurian plate)-PH (Philippine Sea plate) convergence affects the southeastern part of the Korean peninsula, of which the direction is curved due to internal faults in Korea, striking nearly perpendicular to the stress trend.

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