Characteristics of site-specific response using the measured data from seismic accelerometers in Pohang Yeongil New Port under 9.12 and Pohang earthquakes

Recently, medium-sized earthquakes such as the Gyeongju 9.12 earthquake (September 12, 2016, M(L) = 5.8) and the Pohang earthquake (November 15, 2017, M(L) = 5.4) occurred in Korea, thereby increasing social concern about earthquakes. Because Korea is not located near the Circum-Pacific Belt, also referred to as the “Ring of Fire”, people in Korea are not used to earthquake disasters. Coastal areas in Korea are lined with multiple mega-cities and major industrial facilities. Most of them constructed on landfill, they have a high threat level to the damage to populations and structures leading to complex disasters in the event of an earthquake. However, studies of seismic hazards in ports is incomplete compared with those of onshore sites. Improving the understanding of seismic hazards and characterizing them catching up with related research from various perspectives being actively conducted. In this study, the site-specific response characteristics of the Pohang International Container Terminal in Pohang Yeongil New Port were analyzed using the S-wave energy of 10 sets of ground motions recorded by seismic accelerometers operated by the Ministry of Oceans and Fisheries based on the horizontal-to-vertical spectral ratio (H/V ratio) method. As a result of analysis, the H/V ratio curves show that the peak frequency values for the target site averages 9 Hz, and the natural period values of the site were preliminarily predicted to average 0.11 s. In addition, site amplification characteristics are different based on the seismic wave calculation method. The result can be used as data for identifying ground dynamic characteristics and verifying the site amplification coefficients and design spectrum in the seismic design.