Crustal S-wave velocity structure beneath Gangwon Province, the Korean Peninsula, inferred from Helmholtz tomography

초록

Gangwon Province, located in the central part of the Korean Peninsula, features northeast-southwest faults and tectonic structures formed by plutonic intrusions. Despite decades of geological investigations from near-surface to the upper crust in Gangwon Province, the lithospheric structure of this region remains poorly understood. The primary objective of this study is to identify velocity anomalies potentially associated with plutonic intrusions and to elucidate the formation processes and mechanisms governing the crustal and upper mantle structures in this region. We employed Helmholtz tomography to generate phase-velocity maps for periods of 10-40 s using a dense seismic network of 101 stations. These maps were subsequently inverted to obtain an S-wave velocity model from the upper crust to the uppermost mantle. Our results reveal northeast-southwest-trending low-velocity anomalies along major faults in central to northern Gangwon Province (i.e. eastern Gyeonggi Massif), extending to depths of approximately 25-30 km. These low-velocity anomalies align with the orientations of Jurassic granitoid intrusions formed through partial melting processes. Additionally, we identified other low-velocity anomalies, likely formed by Late Cretaceous intrusions, which are oriented perpendicular to the major faults. In contrast, the southeastern Gangwon Province (i.e. Taebaeksan Basin) exhibits a distinctly different velocity structure, lacking features indicative of granitic intrusions and showing low-velocity anomalies confined to shallow depths. The pronounced low-velocity anomalies observed at depths of 5-10 km in Taebaeksan Basin are attributed to a complex fault zone influenced by Permo-Triassic collisional orogeny.

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