The Relationship between Bedrock Depth and Site Fundamental Frequency in the Nakdonggang Delta Region, South Korea

Abstract

This paper describes the relationship between bedrock depth (D) and site fundamental frequency (f0) in the Nakdonggang delta region in the southeastern part of the Korean peninsula. We collected borehole logs to confirm the thickness of the sediments and estimated the f0 at over 200 locations across the delta using the horizontal-to-vertical spectral ratio (HVSR) method. We developed an f0 map of the study area by spatially interpolating the f0 values using the Ordinary Kriging method. The bedrock depth in the main delta showed a power-law dependence on the f0. The derived f0–D model predicted much shallower bedrock depths compared with similar studies from other parts of the world. This was attributed to the fact that the Nakdonggang delta region is composed of relatively low Vs Holocene sediments. With an f0 map, the derived model could enable a quick estimation of the bedrock depth, which could help to determine the site class in the Nakdonggang delta region according to the Korean Seismic Design Standard (KDS 17 10 00).