A moment magnitude 5.4 earthquake struck the Pohang city located in the southeastern Korean Peninsula on 15 November 2017, possibly triggered by an enhanced geothermal system. Despite the moderate magnitude of the earthquake, extensive geotechnical and structural damage occurred. This study summarizes the widespread geotechnical damage resulted from the Pohang earthquake, observed during our reconnaissance trip. The affected area is mainly covered by Tertiary/Quaternary Alluvium underlain by mudstones with a thickness of approximately 500 m. Because of the soft grounds and shallow focal depth, this area experienced ground settlements up to 39 cm, building settlements that made apartments tilted by 1.6°. We also present observations on ground cracks, lateral spreadings, landslides, retaining wall deformations, and liquefactions. Documenting the damage is significant because (1) those are the first earthquake-induced damage observed in Korea, and (2) those are caused by the shallow-depth earthquake possibly induced by an enhanced geothermal system.

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A method for transforming planar electronic devices into 3D structures under mechanically mild and stable conditions is demonstrated. This strategy involves diffusion control of acetone as a plasticizer into a spatially designed acrylonitrile butadiene styrene (ABS) framework to both laminate membrane-type electronic devices and transform them into a desired 3D shape. Optical, mechanical, and electrical analysis reveals that the plasticized region serves as a damper and even reflows to release the stress of fragile elements, for example, an Au interconnect electrode in this study, below the ultimate stress point. This method also gives considerable freedom in aligning electronic devices not only in the neutral mechanical plane of the ABS framework, which is the general approach in flexible electronics, but also to the top surface, without inducing electrical failure. Finally, to develop a prototype omnidirectional optical system with minimal aberrations, this method is used to produce a bezel-less tetrahedral image sensor.

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Over 160 shallow landslides resulted from heavy rainfall that occurred in 26–27 July 2011 at Umyeon Mountain, Seoul, South Korea. To accurately reflect the fluid flow mechanism in the void spaces of soils, we considered the two-phase flow of water and air for rainfall infiltration analysis using available historical rainfall data, topographic maps, and geotechnical/hydrological properties. Variations in pore water and air pressure from the infiltration analysis are used for slope stability assessment. By comparing the results from numerical models applying single- and two-phase flow models, we observed that air flow changes the rate of increase in pore water pressure, influencing the safety factor on slopes with a low infiltration capacity, where ponding is more likely to occur during heavy rainfall. Finally, several slope failure assessments were conducted to evaluate the usefulness of using the two-phase flow model in forecasting slope stability in conditions of increased rainfall sums. We observed that the two-phase flow model reduces the tendency of over-prediction compared to the single-phase model. The results from the two-phase flow model revealed good agreement with actual landslide events.