Brief Communication : A case study of risk assessment for 1 facilities associated with earthquake-induced liquefaction 2 potential in Kimhae City , South Korea 3 4

Liquefaction causes secondary damage after earthquakes; however, liquefaction related phenomena were 14 rarely reported until after the Mw = 5.4 November 15, 2017 Pohang earthquake in Korea. Both the Mw = 5.8 September 15 12, 2016 Gyeongju earthquake and Mw = 5.4 November 15, 2017 Pohang earthquake occurred in the fault zone of 16 Yangsan City (located in the south-eastern part of South Korea), and both of these earthquakes induced liquefaction. 17 Moreover, they demonstrated that Korea is not safe against the liquefaction induced by earthquakes. In this study, 18 estimations and calculations were performed based on the distances between the centroids of administrative districts 19 and an epicenter located at the Yangsan Fault, the peak ground accelerations (PGAs) induced by Mw = 5.0 and 6.5 20 earthquakes, and a liquefaction potential index (LPI) calculated based on groundwater level and standard penetration 21 test results from 274 locations in Kimhae City (adjacent to the Nakdong river and across the Yangsan Fault). Then, a 22 kriging method using geographical information systems was used to evaluate the liquefaction effects on the risk levels 23 of facilities. The results indicate that a Mw = 5.0 earthquake induces a small and low level of liquefaction, resulting in 24 slight risk for facilities, but a Mw = 6.5 earthquake induces a large and high level of liquefaction, resulting in a severe 25 risk for facilities. 26 27 28

https://doi.org/10.5194/nhess-2021-287 Preprint. Discussion started: 21 October 2021 c Author(s) 2021. CC BY 4.0 License. groundwater level and peak ground acceleration (PGA) induced by earthquake loading, and it represents the 48 liquefaction potential. There is no liquefaction when the FS is equal to or greater than 1.0; by contrast, it has the 49 potential for liquefaction when the FS is less than 1.0. However, a liquefaction potential estimated using the FS 50 cannot represent the ground damage for broad areas; rather, it is only applicable to local specific areas. The LPI 51 proposed by Iwaski et al. (1982) has been used to estimate the hazards induced by liquefaction in broad areas and to 52 produce corresponding hazard maps (Chung and Rogers, 2011;Iwasaki et al., 1982;Lee et al., 2003).

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When an earthquake occurs, the liquefaction potential is determined by the groundwater level and PGA associated 54 with the ground characteristics. In this study, the safety of facilities in Kimhae City (located in the south-eastern part 55 of Korea) was estimated based on attenuation equations associated with the distance from the epicenter to the centroid 56 of seventeen administrative districts in Kimhae City. The Pohang earthquake, the largest recent earthquake in Korea, 57 had a magnitude of 5.0. An earthquake magnitude of 6.5, corresponding to a PGA of 0.2g, is the standard for the 58 design of earthquake-resistant structures in Korea. Therefore, in this study, the FS values for facilities in Kimhae 59 City were estimated for Mw 5.0-and 6.5-earthquakes, and the liquefaction potential was evaluated based on currently 60 available standard penetration test (SPT) results. Since cone penetration test (CPT) results can reflect more precise

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In this study, the LPI proposed by Iwasaki et al. (1978) was used to estimate the ground damage level induced by 68 liquefaction. As described in Eqn. (1), the LPI is calculated based on the ground depth and characteristics of soil, as

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(1) provides LPIs in the range from 0 to 100. Iwasaki et al. (1978) proposed levels of liquefaction severity, as 75 described in Table 1, associated with 63 and 22 areas at liquefaction and non-liquefaction sites, respectively.

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The PGA induced by an earthquake has large variations associated with the soil characteristics, distance from the 103 epicenter, and ground depth. As the PGA is a crucial factor, it is directly used to evaluate earthquake-induced damage.

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The largest PGA normally occurs near the epicenter, and the PGA generally decreases as the distance from the 105 epicenter increases. In this study, the PGA was evaluated based on both the distance from each administrative district

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Facilities in Kimhae City are categorized as described in Table 4.

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The "very high" and "high" level of liquefaction severity for the Mw = 5.0 earthquake cover 2 km 2 (0.2%) and 22.1 193 km 2 (4.8%) of the study area, respectively. The "very high" and "high" level of liquefaction severity for the Mw = 6.5 194 earthquake cover 28.6 km 2 (6.2%) and 11.5 km 2 (2.5%) of the study area, respectively. These areas seem to be small 195 in proportion to the total area, but are not small in proportion to the plat area. As the earthquake magnitude increases 196 from Mw = 5.0 to Mw = 6.5, the proportion of land with high level of liquefaction severity increases substantially.
197 Figure 6 shows bridges, buildings, and water pipelines superimposed on the spatial distribution of the LPI for both 198 the Mw = 5.0 and 6.5 earthquakes. Figure 7 shows how facilities are distributed in level of liquefaction severity zones.  Table 5 shows the ratios of facilities corresponding to various LPI ranges for the 217 Mw = 5.0 earthquake. As the earthquake magnitude increases from 5.0 to 6.5, the risk levels of facilities increase.  Table 6 shows the ratios of facilities corresponding to various level of liquefaction severity 223 ranges for the Mw = 6.5 earthquake.

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2. Areas with very low and high level of liquefaction severity for an earthquake magnitude of 6.5 cover 83%

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(381.4 km 2 ) and 2.5% (11.5 km 2 ) of the total area, respectively. As the earthquake magnitude changes from

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whereas some change to very high level of liquefaction severity for the earthquake magnitude of 6.5. This

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indicates that an Mw = 6.5 earthquake may result in higher risks levels for facilities associated with high level 253 of liquefaction severity.

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3. The areas with high level of liquefaction severity for the earthquake magnitude of 5.0 cover less than 0.1% of 256 roadways, sewage pipelines, and public facilities. In addition, 80% of facilities (except light rail transit 257 facilities) correspond to very low level of liquefaction severity. Therefore, the liquefaction-induced risk levels 258 for facilities are very low for the Mw = 5.0 earthquake. However, as the earthquake magnitude increases to 259 6.5, 9% of facilities (except for tunnel and railway facilities) and 30% of light rail transit facilities are 260 distributed in high level of liquefaction severity areas, reflecting higher risk levels for these facilities. 261 262 4. The SPT database for Kimhae City was used to estimate the CSR and LPI. Higher LPI values are found at 263 the sedimentary layers of soils widely distributed adjacent to Nakdong river. Importantly, a magnification of 264 ground movement occurs near the fault zone during an earthquake. Therefore, the construction of buildings 265 in regions with high liquefaction severity should be avoided. 266 267 268