Paleoseismological implications of liquefaction-induced structures caused by the 2017 Pohang Earthquake

Springer Science and Business Media LLC - Tập 22 - Trang 871-880 - 2018
Yong Sik Gihm1, Sung Won Kim1, Kyoungtae Ko2, Jin-Hyuck Choi1, Hankyung Bae1, Paul S. Hong1, Yuyoung Lee1, Hoil Lee3, Kwangmin Jin2, Sung-ja Choi4, Jin Cheul Kim3, Min Seok Choi5, Seung Ryeol Lee1
1Geology Division, Korea Institute of Geoscience and Mineral Resources, Daejeon, Republic of Korea
2Climate Change Mitigation and Sustainability Division, Korea Institute of Geoscience and Mineral Resources, Daejeon, Republic of Korea
3Geologic Environment Division, Korea Institute of Geoscience and Mineral Resources, Daejeon, Republic of Korea
4Geoscience and Technology Dissemination Division, Korea Institute of Geoscience and Mineral Resources, Daejeon, Republic of Korea
5Department of Geological Science, Pusan National University, Busan, Republic of Korea

Tóm tắt

During and shortly after the 2017 Pohang Earthquake (Mw 5.4), sand blows were observed around the epicenter for the first time since the beginning of instrumental seismic recording in South Korea. We carried out field surveys plus satellite and drone imagery analyses, resulting in observation of approximately 600 sand blows on Quaternary sediment cover in this area. Most were observed within 3 km of the epicenter, with the farthest being 15 km away. In order to investigate the ground’s susceptibility to liquefaction, we conducted a trench study of a 30 m-long sand blow in a rice field 1 km from the earthquake epicenter. The physical characteristics of the liquified sediments (grain size, impermeable barriers, saturation, and low overburden pressure) closely matched the optimum ground conditions for liquefaction. Additionally, we found a series of soft sediment deformation structures (SSDSs) within the trench walls, such as load structures and water-escaped structures. The latter were vertically connected to sand blows on the surface, reflecting seismogenic liquefaction involving subsurface deformation during sand blow formation. This genetic linkage suggests that SSDS research would be useful for identifying prehistoric damage-inducing earthquakes (Mw > 5.0) in South Korea because SSDSs have a lower formation threshold and higher preservational potential than geomorphic markers formed by surface ruptures. Thus, future combined studies of Quaternary surface faults and SSDSs are required to provide reliable paleoseismological information in Korea.

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