Crustal Structure of Gangwon Province in the Korean Peninsula from Helmholtz Tomography

Gangwon Province, located in the central part of the Korean Peninsula, is distinguished by fault structures that primarily follow a northeast-southwest orientation. Understanding the subsurface structure of this region is essential for assessing seismic hazards and accurately measuring seismicity. A recently deployed dense seismic network, with an average lateral spacing of ~50 km, enables the construction of a high-resolution crustal velocity model. We employed Helmholtz tomography using 101 broadband seismometers and accelerometers and 261 teleseismic events with epicentral distances of 5-90°, to obtain phase-velocity maps for periods of 10 to 40 s. By inverting these phase-velocity maps, we derived an S-wave velocity model spanning depths from the shallow crust to the uppermost mantle (5 to 50 km). Our results revealed northeast-southwest trending low-velocity anomalies along major faults in northern Gangwon Province, extending to depths of ~25 km. These low-velocity anomalies correspond to the intrusion orientations of granitic bodies generated through partial melting during the Mesozoic era. In contrast, the southern Gangwon Province exhibits a distinctly different velocity structure, lacking features indicative of granitic intrusions and showing low-velocity anomalies confined to shallow depths.