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Reactivation of ancient rift systems triggers devastating intraplate earthquakes
Author(s) -
Kato Aitaro,
Kurashimo Eiji,
Igarashi Toshihiro,
Sakai Shinichi,
Iidaka Takashi,
Shinohara Masanao,
Kanazawa Toshihiko,
Yamada Tomoaki,
Hirata Naoshi,
Iwasaki Takaya
Publication year - 2009
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/2008gl036450
Subject(s) - intraplate earthquake , geology , rift , seismology , crust , aftershock , basement , seismometer , east african rift , rift zone , tectonics , geophysics , civil engineering , engineering
Large historical and recent intraplate earthquakes have been concentrated along a contractional zone at the eastern margin of the Japan Sea back‐arc basin. Here we present high‐resolution three‐dimensional tomographic imaging of seismic velocities in this zone using data from a dense seismograph deployment. We discover that stepwise and tilted block structures of the basement, which are geophysical evidence of a Miocene rift system, are widely distributed beneath the thick sedimentary basin. Most aftershocks following recent intraplate earthquakes align roughly along the tilted block boundaries and are controlled by weaknesses associated with buried rift systems. Furthermore, slow anomalies are localized beneath the seismogenic zones, suggesting that fluids may have locally weakened the strength of the lower crust. We propose that stress loading through ductile creeping of the weak lower crust reactivates pre‐existing weak faults within ancient rift systems, leading to devastating intraplate earthquakes.