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A Comparative Study Between the Resonance Frequency by Hvsr Analysis and Bedrock Depth in Western Busan, Korea

Nakdong River is one of the major rivers in Korea that runs through the Busan metropolitan area. During the 1.6 km long bridge construction across the river, twenty-seven boreholes were drilled to measure the depth of the bedrock. This study determines the resonance frequencies at the borehole sites using the HVSR (Horizontal-to-vertical spectral ratio) technique and compares the results with direct measurements. Bedrock depths from the 27 borehole measurements vary from 38 to 70 meters. Although their variations are not serious along the 3.8 km long route, a relatively sharp decrease in the bedrock depth was noticed near the borehole NSB-5 (~38 meters). We collected ambient noise data at locations near 27 boreholes in 2022 and estimated resonant frequencies using the HVSR technique. Resonance frequencies from HVSR vary from 0.9 Hz to 1.3 Hz. A relatively high resonance frequency, 1.3 Hz, is estimated at NSB-5, which is consistent with the observations from the direct measurements from boreholes. Details of the boring logs indicate that the sedimentary layers consist of multiple lithologic layers, including reclaimed soil, silt sand, silt clay, and sand-mixed silt gravel. Since their impedance contrasts are not significant, it is not evident from the HVSR curves. This study demonstrated a significant correlation between the depth of bedrock identified in boreholes and the resonance frequency obtained through HVSR analysis using microtremor observations. HVSR analysis effectively reflected the bedrock depth at the microtremor observation sites.

Session: How Well Can We Predict Broadband Site-Specific Ground Motion and Its Spatial Variability So Far? [Poster Session]

Type: Poster

Room: Exhibit Hall

Date: 5/1/2024

Presentation Time: 08:00 AM (local time)

Presenting Author: Su Young Kang

Student Presenter: No

Additional Authors