Ground Motion Amplifications at the Embankments of Reservoirs in South Korea

Abstract

The 2017 local magnitude (ML) 5.4 Pohang, South Korea, earthquake caused minor damage to four agricultural reservoir embankments within a radius of 100 km from the epicenter. It is well known that the earthquake ground1 motions can be altered by subsurface soil conditions and surface topographies. To understand the ground motion characteristics at the reservoir sites in Korea, this study utilizes ground motions recorded at 70 sites during nine earthquakes with ML ranging from 2.0 to 3.9 that occurred from July 21, 2019 to June 30, 2022. At each of these 70 sites, motions are recorded at three locations: the crest of the embankment, the toe of the embankment, and 30 m below the free field (borehole). It turns out that ground motion amplification factors decrease with the VS30 and peak ground acceleration of the borehole ground motion. Furthermore, the ground motions at both the toe and crest of the embankment are significantly influenced by the geometry of the embankment. The ground motion amplification factors increase with the width of the embankment up to a certain width, and subsequently decrease again. The width of the embankment at the apex of the amplification factors increases with the period, indicating the effect of interactions between waves of various wavelengths and embankments of various sizes. We propose predictive models for ground motion amplification for various periods