Helium isotopes as a tool for detecting concealed active faults

2014 Fiscal Year Final Research Report

• Project/Area Number: 24510250
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Research Field: Natural disaster science
• Research Institution: Japan Atomic Energy Agency
• Principal Investigator: UMEDA Koji 独立行政法人日本原子力研究開発機構, バックエンド研究開発部門 東濃地科学センター, リーダー (60421616)
• Co-Investigator(Kenkyū-buntansha): ASAMORI Koichi 独立行政法人日本原子力研究開発機構, バックエンド研究開発部門 東濃地科学センター, 研究員 (80421684) ; SUEOKA Shigeru 独立行政法人日本原子力研究開発機構, 高速炉研究開発部門 もんじゅ運営計画・研究開発センター, 技術職 (80634005)
• Project Period (FY): 2012-04-01 – 2015-03-31
• Keywords: 活断層 / ヘリウム同位体

Outline of Final Research Achievements

This study was undertaken to elucidate spatial and temporal changes of 3He/4He ratios around a source region before and after an inland earthquake using both existing and new and helium isotope data from hot spring and drinking water wells. Gas samples near the main active fault and its surrounding faults are characterized by an increase in postseismic 3He/4He ratios. In contrast, the postseismic ratios decreased by up to about 30 % away from the mainshock epicenter. Episodic faulting could either release stored crustal (radiogenic) helium from host rocks, or enhance the transfer of mantle volatiles through permeable fault zones, such that subsequent fluid flow near to the source region could then explain the spatio-temporal variations in 3He/4He ratios. Consequently, helium isotopes can be regarded as a tool for investigating and/or mapping concealed active faults with no surface expression.

Free Research Field

自然災害科学