Lee Hyunwoo, Kim Heejun, Kagoshima Takanori, Park Jin-Oh, Takahata Naoto, Sano Yuji
School of Earth and Environmental Sciences, Seoul National University, 1 Gwanak-ro, Gwanak-gu, Seoul, 08826, Republic of Korea.
Atmosphere and Ocean Research Institute, University of Tokyo, Kashiwa, Chiba, 277-8564, Japan.
Sci Rep. 2019 Oct 25;9(1):15334. doi: 10.1038/s41598-019-51719-3.
On September 12, 2016, a M 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 (CO) in fault-related fluids in the region. Based on gas geochemistry, the majority of gas samples are abundant in CO (up to 99.91 vol.%). Measured He/He ratios range from 0.07 to 5.66 Ra, showing that the mantle contribution is up to 71%. The range of carbon isotope compositions (δC) of CO is from -8.25 to -24.92‰, showing mantle-derived CO is observed coherently where high He/He ratios appear. The weakening of faults seems to be related to enhanced pressures of fluids containing mantle-derived helium and CO despite the ductile lower crust underneath the region. Thus, we suggest that the SeKP strike-slip faults penetrate into the mantle through ductile shearing.
2016年9月12日，一场里氏5.8级地震袭击了朝鲜半岛东南部的庆州，尽管该地区据知远离活动板块边界。在人口密集的城市地区（如釜山、蔚山、浦项和庆州）观测到了许多走滑断层。然而，尽管该地区有许多地下水井和温泉，但与活动断层相关的溶解气体却很少被研究。在此，我们报告该地区与断层相关流体中氦气和二氧化碳（CO）的气体成分及同位素值的新结果。基于气体地球化学，大多数气体样本富含CO（含量高达99.91体积%）。测得的³He/⁴He比值范围为0.07至5.66 Ra，表明地幔贡献高达71%。CO的碳同位素组成（δ¹³C）范围为 -8.25至 -24.92‰，表明在³He/⁴He比值高的地方一致观测到了地幔来源的CO。尽管该地区下方的下地壳具有韧性，但断层的弱化似乎与含有地幔来源氦气和CO的流体压力增强有关。因此，我们认为朝鲜半岛东南部的走滑断层通过韧性剪切作用穿透到了地幔中。
