The southeastern Korean Peninsula (SeKP) has experienced intense deformation owing to subduction and backarc extension at the eastern continental margin of the Eurasian Plate, leading to the formation of complex tectonic structures. Abnormally high surface heat flux, Cenozoic volcanism, signatures of mantle degassing and hydrothermal alteration, and several active fault systems with extensional sedimentary basins have been identified; however, the major driving forces that promote local seismic events and hydrothermal activities remain enigmatic. Here, we constructed 3-D P-wave velocity of the crust and upper mantle in the SeKP for the first time using a teleseismic traveltime tomography method and an extensive data set obtained from a dense seismic network. Our model revealed three distinct velocity patterns at different depths: (1) in the upper crust (depth ∼0-10 km), a low-velocity anomaly beneath the Cenozoic sedimentary basin exhibiting a prominent lateral velocity contrasts with higher velocities in the Cretaceous sedimentary and plutonic rocks; (2) a N-S trending low-velocity anomaly extending from the lower crust to the uppermost mantle (depth ∼20-35 km) beneath the major active fault systems interpreted as a thermally or mechanically weakened structure that could transfer high surface heat flux and transport mantle-driven gases and (3) a low-velocity anomaly adjacent to the Cenozoic basin in the upper mantle at depths of 35-55 km interpreted as the higher temperature upper mantle. Via a series of geodynamic simulations, we demonstrated that the extensional deformation at the eastern continental margin during the Early to Middle Miocene locally enhanced the temperature of the crust and upper mantle beneath the SeKP. We propose that a hydrothermal system, resulting from the thermally modified lithosphere of the continental margin, has contributed to the enhanced local seismicity and geothermal activities observed in the SeKP region.
Bibliographical noteFunding Information:
We thank Dr Ian Bastow, Dr Simone Pilia and one anonymous reviewer for constructive comments and suggestions that improved the original manuscript. We thank the CIG ( geodynamics.org ), funded by the National Science Foundation under awards EAR-0949446 and EAR-1550901, for supporting the development of ASPECT. We acknowledge Dr Nicholas Rawlinson for making the codes (Fast-Marching Teleseismic Tomography and Adaptive Stacking) available and providing constructive comments. Figures in this article were generated using the Generic Mapping Tools ver. 6.0.0 ( https://www.generic-mapping-tools.org/ ), Matplotlib ver. 3.3.4 ( https://matplotlib.org/ ) and Inkscape ver. 0.92.5 ( https://inkscape.org/ ). We used a scientific colour map provided by Crameri et al. () as a colour bar for tomographic images. The temporary seismic network data in this study were acquired from the NSSC under its authorization. This study was funded by the Korea Meteorological Institute under grant KMI2022-00910.
© 2023 The Author(s). Published by Oxford University Press on behalf of The Royal Astronomical Society.
- Continental margins: convergent
- Crustal structure
- Hydrothermal system
- Numerical modelling
- Southeastern Korean Peninsula
- Teleseismic traveltime tomography
ASJC Scopus subject areas
- Geochemistry and Petrology