Development of predominant-period and average S-wave velocity maps for Hue City, Central Vietnam

We have developed maps of the predominant period of the ground and average S-wave velocity to depths of 10, 20 and 30 m (VS10, 20 and 30) as the fundamental data for seismic hazard assessment for Hue City, Central Vietnam. We conducted microtremor single-station measurements at 461 sites and microtremor array measurements at 157 sites in and around the city (i.e., within an area of about 15 km x 15 km). The peak period of horizontal-to-vertical spectral ratios (HVSR) obtained from three-component microtremor waveforms at a single station were regarded as a S-wave predominant period of the ground. Rayleigh-wave phase velocity at wavelengths of 13, 25 and 40 m obtained from vertical-component array measurements were regarded as VS10, 20 and 30, respectively. It revealed that the predominant periods range from 0.03 to 1.98 s (i.e., 0.5 to 33 Hz) in Hue City, which show a tendency to be longer in the northern part of the city than in the southern part. The analysis results of the average S-wave velocity indicate that soft sediments are very thick in the northern part of the city, where VS10, 20 and 30 ranges from 149 to 189 m/s. These analysis results are consistent with an existing geological map and quantify the geoenvironmental conditions in Hue City, indicating the effectiveness of the microtremor measurements for a seismic assessment.