Comparative analyses of seismic site conditions and microzonation of the major cities in Gangwon Province, Korea

Abstract

To determine the seismic site conditions and microzonation of Chuncheon, Wonju and Gangneung cities in the Gangwon Province, Korea, the dispersion curves of Rayleigh waves were derived at 313 sites by the extended spatial autocorrelation (ESPAC) method. Using the shear-wave velocities (Vs) determined from dispersion curves, average depth to the bedrock (Db) and Vs at the top of the bedrock (Vsb), the overburden layer (Vso) and the top 30m depth layer (Vs30) were determined. The resonance frequencies (fr) were then computed using both Db and Vso. The estimated averages of the three cities were 13 7m for Db, 472 109m/s for Vsb, 248 44m/s for Vso, 411 157m/s for Vs30 and 5.8 2.8Hz for fr. Microzonation maps based on the proxy-based Vs30 indicated that the three cities were mainly categorised into National Earthquake Hazards Reduction Program (NEHRP) classes B, C and D, with a minor proportion of A. Although no area was estimated to be in class E using the proxy-based Vs30, the Vs30 values derived from the recorded Rayleigh waves at 13 sites in Gangneung were less than 180m/s. This indicates a greater vulnerability to seismic amplification during large earthquakes in this city, which had the smallest Vso, Vs30 and fr, and the greatest Db of the three cities. Microzonation maps, together with information for fr, can be effectively used for seismic risk assessments, urban planning, and disaster management.