Preliminary results of the seismic microzonation and site characterization of three major cities of Gangwon province, Korea using Rayleigh-wave dispersion curves

Abstract

To define the seismic site conditions in the three major cities (Chuncheon, Wonju and Gangneung) of Gangwon province, Rayleigh-wave data were recorded using both passive and active sources. An 8-kg wooden hammer was used as an active source. The seismic waves were recorded for 8 to 64 s using twelve or twenty four 4.5-Hz geophones and digitally recorded on a 24-channel engineering seismograph at 125 to 500 Hz sample rates. Phase-velocity spectra of the Rayleigh waves were obtained by the extended spatial autocorrelation method. Shear-wave velocity models were derived from the estimated dispersion curves determined from the phase velocity spectra using the damped least-squares inversion technique. From these 1-D velocity models, estimated values of Vs30 in Chuncheon, Wonju and Gangneung are 402±13 m/s, 418±13 m/s, and 365±15 m/s, respectively. Most of the investigated areas in those cities belong to NEHRP site class D, C, E and B. In downtown and agricultural areas, both the lower estimates of Vs30 and thicker overburden layer make them more prone to significant ground amplifications. The Vs30 estimates show that Chuncheon and Wonju are at lower risk of ground shaking effects than Gangneung in case seismic activities.