The buckling structure and reactivation of faults along eastern margin of Korean peninsula: Implications for recent seismicity in southeast Korea.
Location：National Central University, Kwoh-Ting Library and Archives, Meeting room 2
Speaker： Byung-Dal So
(Division of Geology and Geophysics, Kangwon National University, Chuncheon 24341, South Korea)
Two moderate earthquakes (i.e., 2016 M L 5.8 Gyeongju and 2017 M w 5.5 Pohang) occurred recently in southeastern part of Korean peninsula. These events have gained great social interest in Korea due to large population and many infrastructures including nuclear power plants in the southeast Korea. The back-arc basins between Korean peninsula and Japan island arc is in the closing stage by EW compression due to far-field tectonic stress (i.e., the advance of Japan trench and stress propagation from Himalaya). Moreover, marine terrace study of the eastern Korean margin supports ongoing uplift of the hanging wall at a rate of 0.26–0.67 m/kyr since at least 0.3 Ma. I suspect that this back-arc basin closing, compressional stress, and its subsequent fault reactivation can explain recent seismic activity. To quantify and analyze the source of earthquakes in continental southeast Korea, it is essential to understand stress regime of seaward region of back-arc basin, Ulleung Basin. In this talk, I will present the compiled geophysical data of Ulleung Basin east of Korean peninsula, then show 2D numerical simulation study for investigating the rheology and stress of the basin and peninsula. I and my colleagues found buckling structure with a wavelength of 60–70 km and an amplitude of 0.15–0.2 km. Furthermore, the seismic data exhibits a tri-shear zone in sedimentary layer at the ocean-continent boundary, which indicates a high angle west-dipping reverse faults. I tried to find best-fit rheology and compression rate to constrain morphology of the buckling structure and uplift-rate of eastern margin of Korean peninsula. In the end of talk, I estimate the magnitude of compressional stress of continental southeast Korea for evaluating a possible magnitude of earthquakes.