Paleoseismology of the Yangsan Fault, southeastern part of the Korean Peninsula

AbstractRecurrence characteristics of a Quaternary fault are generally investigated on the basis of field properties that are rapidly degraded by chemical weathering and erosion in warm humid climates. Here we show that in intense weathering environments, mineralogical and micromorphological investigations are valuable in paleoseismological reconstruction. A weathering profile developed in Late Quaternary marine terrace deposits along the southeastern coast of the Korean Peninsula was disturbed by tectonic movement that appears to be a simple one-time reverse faulting event based on field observations. A comparative analysis of the mineralogy, micromorphology, and chemistry of the weathering profile and fault gouge, however, reveals that both the microfissures in the deformed weathering profile and larger void spaces along the fault plane were filled with multi-stage accumulations of illuvial clay and silt minerals of detrital origin, suggesting a repetition of fissuring and subsequent sealing in the weathering profile as it underwent continuous mineralogical transformation and particle translocation. We reconstruct a sequence of multiple faulting events unrecognized in previous field surveys, which requires revision of the view that the Korean Peninsula was tectonically stable, during the Late Quaternary.

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Factors influencing natural occurrence of fluoride-rich groundwaters: a case study in the southeastern part of the Korean Peninsula

Chemosphere ◽

10.1016/j.chemosphere.2004.10.002 ◽

2005 ◽

Vol 58 (10) ◽

pp. 1399-1408 ◽

Cited By ~ 153

Author(s):

Kangjoo Kim ◽

Gi Young Jeong

Keyword(s):

Korean Peninsula ◽

Natural Occurrence ◽

Southeastern Part ◽

Factors Influencing

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Mantle degassing along strike-slip faults in the Southeastern Korean Peninsula

Scientific Reports ◽

10.1038/s41598-019-51719-3 ◽

2019 ◽

Vol 9 (1) ◽

Cited By ~ 2

Author(s):

Hyunwoo Lee ◽

Heejun Kim ◽

Takanori Kagoshima ◽

Jin-Oh Park ◽

Naoto Takahata ◽

...

Keyword(s):

Carbon Dioxide ◽

Korean Peninsula ◽

Lower Crust ◽

Hot Springs ◽

Active Faults ◽

Strike Slip ◽

Southeastern Part ◽

Ductile Shearing ◽

Groundwater Wells ◽

Ductile Lower Crust

Abstract On September 12, 2016, a ML 5.8 earthquake hit Gyeongju in the southeastern part of the Korean Peninsula (SeKP), although the area is known to be far from the boundary of the active plate. A number of strike-slip faults are observed in heavily populated city areas (e.g., Busan, Ulsan, Pohang, and Gyeongju). However, dissolved gases related to the active faults have rarely been studied despite many groundwater wells and hot springs in the area. Here we report new results of gas compositions and isotope values of helium and carbon dioxide (CO2) in fault-related fluids in the region. Based on gas geochemistry, the majority of gas samples are abundant in CO2 (up to 99.91 vol.%). Measured 3He/4He ratios range from 0.07 to 5.66 Ra, showing that the mantle contribution is up to 71%. The range of carbon isotope compositions (δ13C) of CO2 is from −8.25 to −24.92‰, showing mantle-derived CO2 is observed coherently where high 3He/4He ratios appear. The weakening of faults seems to be related to enhanced pressures of fluids containing mantle-derived helium and CO2 despite the ductile lower crust underneath the region. Thus, we suggest that the SeKP strike-slip faults penetrate into the mantle through ductile shearing.

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