Open AccessHigh 3 He emanations from the source regions of recent large earthquakes, central Japan
Author(s) -
Umeda Koji,
Ninomiya Atusi,
McCrank Glen F.
Publication year - 2008
Publication title -
geochemistry, geophysics, geosystems
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.928
H-Index - 136
ISSN - 1525-2027
DOI - 10.1029/2008gc002272
Subject(s) - geology , mantle (geology) , lithosphere , crust , seismology , mantle wedge , slab , isotopes of helium , helium , subduction , geophysics , tectonics , physics , atomic physics
Recently, two shallow M W 6.6 inland earthquakes, the 2004 mid‐Niigata prefecture earthquake and the 2007 Niigataken Chuetsu‐oki earthquake, occurred in the Niigata sedimentary basin near the boundary between the Eurasian and the North American Plates. In order to elucidate the geographic distribution of the 3 He/ 4 He ratios in and around the seismic source regions, new helium isotope data from hot spring gases and water samples from much denser sampling than in previous studies were determined. Although temporal changes in the 3 He/ 4 He ratios obtained from each well were unknown before and after the earthquakes, higher 3 He/ 4 He ratios were observed in the earthquake source regions compared to other regions. Geochemical evidence for the presence of hot spring gases and natural gases with anomalously high 3 He/ 4 He ratios (>3.8 R A ) indicates infiltration of mantle fluids derived from the subcrustal lithosphere. A plausible source of mantle helium can be attributed to upward mobilization of aqueous fluids generated by dehydration of the subducting Pacific Plate slab, resulting in the acquisition of primordial helium from a mantle wedge as the fluids into the crust. In addition, aqueous fluids may raise the Earth's surface along permeable conduits leading to the reactivation of high‐angle inverted normal faults and the triggering of recent earthquakes.