Release of mantle and crustal helium from a fault following an inland earthquake

Post-earthquake anomalies in He–CO2 isotope and relative abundance systematics of thermal waters: The case of the 2011 Van earthquake, eastern Anatolia, Turkey

“…A similar case of contrasting responses in 3 He/ 4 He ratios following seismic activity (i.e., Group I vs. Group II in this study) was reported by Umeda et al (2013) for the 2011 Tohoku-Oki earthquake, a major megathrust, and one of its aftershocks, the central Nagano earthquake located on the reactivated Gofukuji strike-slip fault. These two faults constitute parts of the Itoigawa-Shizuoka Tectonic Line (ISTL) which is considered to be the plate boundary between the North American (or Okhotsuk) and Eurasian (Amurian) Plates.…”

“…These two faults constitute parts of the Itoigawa-Shizuoka Tectonic Line (ISTL) which is considered to be the plate boundary between the North American (or Okhotsuk) and Eurasian (Amurian) Plates. Umeda et al (2013) reported that post-earthquake changes were characterized by an increase in 3 He/ 4 He ratios in samples from the Gofokuji strike-slip fault at the middle part of ISTL, with a decrease in 3 He/ 4 He for samples at reverse faults at the northern and southern segments of ISTL. They attributed these observations to the better developed permeability of strike-slip faults compared to reverse faults occurring under compressional stress.…”

“…This stems from the observation that mantle-and crustal-derived gases are marked by distinct 3 He/ 4 He ratios of 8.0 R A (Graham, 2002) and~0.05 R A (Andrews, 1985), respectively, where R A equals the air 3 He/ 4 He ratio of 1.4 × 10 −6 (Ozima and Podosek, 1983). In such monitoring studies, post-seismic 3 He/ 4 He values -usually corrected for the presence of any air-derived Hehave been found to both decrease, due to degassing of radiogenic helium stored in the crust (e.g., 1995 Kobe earthquake - Sano et al, 1998), and increase, due to addition of mantle-He to the volatile inventory (e.g., 2011 central Nagano earthquake - Umeda et al, 2013). Such changes are likely site-specific, reflecting localized variations in crustal permeability and/or stress-strain relationships in the crust (Sano et al, 1998).…”

“…Monitoring gas geochemistry of fluids from earthquake prone regions has received increasing attention in recent years in order to understand the behavior of fluids within the crust and their relationship to seismicity (e.g., King, 1986;Hilton, 1996;Toutain and Baubron, 1999;Italiano et al, 2001;de Leeuw et al, 2010;Umeda et al, 2013). Helium isotopes have been widely utilized, in this respect, to trace volatile provenance and to monitor the effects of seismic activity which may modify the balance between the inputs of mantle and crustal components to the total helium inventory (e.g., Hilton, 1996;Sano et al, 1998;Italiano et al, 2001).…”

Hot Spring Gas Geochemistry in Western Sichuan Province, China After the Wenchuan Ms 8.0 Earthquake

“…The geophysical data in LMSF also indicated that the lower velocity bodies under the main shock area and aftershocks in western Sichuan Province can be related to mantle fluid upwelling or partial melting (Lei and Zhao 2009;Zhang et al 2009;Wang et al 2010Wang et al , 2011Bai et al 2011). Gas samples collected near the Gofukuji fault and its surrounding active faults are characterized by an increase in post seismic 3 He/ 4 He ratios in the main shock epicenter after the M w 5.4 central Nagano earthquake (Umeda et al 2013).…”