Characteristics of Ground Motions Generated by the 2017 M5.4 Pohang, South Korea Earthquake

Date: 4/25/2019

Time: 06:00 PM

Room: Grand Ballroom

The November 15, 2017 M5.4 Pohang earthquake was recorded as the second largest instrumented earthquake in South Korea, causing serious damages to structures and infrastructure. The ground motions generated by this earthquake were well recorded at seismic stations of the KMA (Korea Meteorological Administration) and the KIGAM (Korea Institute of Geoscience And Mineral Resources). The KMA also installed nine temporary seismic stations immediately after the main-shock event near the epicenter. We analyzed characteristics of the ground motions measured at these regular and temporary seismic stations during the aftershocks with magnitudes ranging from 2.5 to 4.6. We found that the recorded ground motions are rich in high frequencies (around 10 Hz) and better match with the NGA-East ground motion prediction equations (GMPEs) than the NGA-West2 GMPEs. We consider this is because of that the bedrock conditions in Korea are similar with those in Central and Eastern North America (CENA). The Pohang city is mainly covered by the Quaternary and Tertiary deposits. There are small basins consisting of soft soil depths and with bedrocks located at approximately a 500-m depth. In addition, the small basins are surrounded by mountains and hills. These complex stratigraphy and soil conditions affected characteristics of the aftershock ground motions. We observed ground motions amplifications at long periods due to site effects. We also observed generation of surface waves generated by the edge of the basins. Furthermore, we clearly observed evidence of the motions reflected at the soil-bedrock boundary with a sharp impedance contrast. We found that these ground motion characteristics are related with the damage pattern.

Presenting Author: Junyoung Lee

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