Evaluation of short active faults reflected from distributed minor surface breaks found at recent inland large earthquakes including the 2016 Kumamoto earthquake

Toda Shinji, Ishimura Daisuke

doi:10.4116/jaqua.58.121

<p>Inland large earthquakes occur not only on major active faults but also in areas no active fault and/or minor short fault mapped. It leads a conservative evaluation that seismogenic fault up to ～20km is hidden or slightly truncated by the surface, and an M～7 earthquake is assigned on each short fault. Based on field investigation and InSAR analysis for the 2016 Kumamoto earthquake, we here counter-argue that some of such minor and low-slip-rate faults might have been developed by insignificant but frequent slips triggered by nearby large earthquakes. Another unique case possibly contributes to better evaluation of such short faults is the recent repeating M～6 earthquakes occurred on March 19, 2011 (M6.1) and November 22, 2016 (M6.3) at Ibaraki-ken-hokubu, in northern Kanto region, Japan. Both shocks have shared the same 4-km-long fault based on InSAR images and field survey. It enables us to interpret some of the short active faults might have been also developed by more frequent slip at only upper seismogenic layer, not involving the entire seismogenic layer, due to M～6 earthquakes. Together with other cases, we discuss the classification of short active faults with regards to slip rate, erosion rate, and seismogenesis, and then tentatively conclude that short active faults not only generate an independent single M～7 earthquake but also behave aseismically or seismically influenced by neighboring major faults.</p>

Evaluation of short active faults reflected from distributed minor surface breaks found at recent inland large earthquakes including the 2016 Kumamoto earthquake

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