2:30 PM - 2:45 PM
[SSS13-09] Reconsideration on subjects of active fault research from the viewpoint of occurrences of earthquake fault since mid-19th century
Keywords:active fault, long-term evaluation, slip-predictable model, historical earthquake
1. Introduction
18 intraplate earthquakes generated earthquake fault since mid-19th century in Japan. I would make a coincidence about subjects on active fault studies for actual disaster mitigation from the viewpoint of location and amount of displacement of earthquake faults in modern era with respect to previous studies.
2. Examples of earthquake faults which occurred without active fault traces detected by geomorphological research and non-characteristic earthquake
7 earthquakes generated earthquake faults in where no active fault could be detected by geomolophological surveys such as fault topography research and interpretation of antecedent filmed air-photos. Except for two earthquakes (the Mid Niigata Prefecture Earthquake in 2004 and Iwate-Miyagi Nairiku Earthquake in 2008: Both accompany with folding), all of them occurred in the Inner zone of the Southwestern Japan arc. However, the subsequent geological survey made clear that the all of their earthquake fault have acted during late Quaternary. And the subsequent trench survey made clear that three earthquake fault since the latest era of 20th century are not characteristic.
3. Personal viewpoints on subjects of active fault research
Location, length, history and average deformation rate are the most important items on the evaluation of earthquake generated by active faults. The location and length are the most reliable data among them, however not a little earthquake faults especially in the Inner Zone of the Southwestern Japan were not geomorphologically traceable as active fault before earthquake. And three non-characteristic Mj 6.2 to 6.8 earthquakes generated earthquake faults during the last 30 years. They suggest that recent active fault research methods would underestimate on paleo activity of faulting events.
It would be needed intensive field survey accompanying with re-interpretation of landforms for determination of location and length of active faults especially in the Inner Zone of the Southwestern Japan Arc. And it would also be needed estimation of equivalency of cumulative seismic moment accumulated after the last faulting for evaluation on the non-characteristic earthquakes as Katsube et al (2017) showed on the that the Nagano Prefecture Kamishiro Fault Earthquake in 2014 occurred in according to the slip-predictable model (Shimazaki and Nakata, 1980).
4. Some advantages of seismic potential evaluation on the basis of slip-predictable model
The recent seismic potential evaluation based on the history of faulting is not always applicable for all active structures especially for broad deformations such as the mid-Niigata Prefecture Earthquake in 2004 and Iwate-Miyagi Nairiku Earthquake in 2008. On the other hand, to make clear the mean displacement rate and the upper limit of the last event age are capable for the most structures which generate vertical displacement, and furthermore to convert them from previous studies would be possible in most other cases. By accounting for these empirical facts, it would be a one of subjects in earthquake evaluation to estimate possible seismic moment by mean slip rate and age (or upper limit age) of the last event on the basis of the slip predictable model.
Please discuss.
Reference
Katsube, A. Kondo, H. and Kurosawa, H. (2017) Surface rupturing earthquakes repeated in the 300 years along the ISTL active fault system, central Japan. Geophysical Research Letters, 44, 6057-6064.
Shimazaki, K. and Nakata, T. (1980) Time-predictable recurrence model for large earthquakes. Geophysical Research Letters, 7, 279-282.
18 intraplate earthquakes generated earthquake fault since mid-19th century in Japan. I would make a coincidence about subjects on active fault studies for actual disaster mitigation from the viewpoint of location and amount of displacement of earthquake faults in modern era with respect to previous studies.
2. Examples of earthquake faults which occurred without active fault traces detected by geomorphological research and non-characteristic earthquake
7 earthquakes generated earthquake faults in where no active fault could be detected by geomolophological surveys such as fault topography research and interpretation of antecedent filmed air-photos. Except for two earthquakes (the Mid Niigata Prefecture Earthquake in 2004 and Iwate-Miyagi Nairiku Earthquake in 2008: Both accompany with folding), all of them occurred in the Inner zone of the Southwestern Japan arc. However, the subsequent geological survey made clear that the all of their earthquake fault have acted during late Quaternary. And the subsequent trench survey made clear that three earthquake fault since the latest era of 20th century are not characteristic.
3. Personal viewpoints on subjects of active fault research
Location, length, history and average deformation rate are the most important items on the evaluation of earthquake generated by active faults. The location and length are the most reliable data among them, however not a little earthquake faults especially in the Inner Zone of the Southwestern Japan were not geomorphologically traceable as active fault before earthquake. And three non-characteristic Mj 6.2 to 6.8 earthquakes generated earthquake faults during the last 30 years. They suggest that recent active fault research methods would underestimate on paleo activity of faulting events.
It would be needed intensive field survey accompanying with re-interpretation of landforms for determination of location and length of active faults especially in the Inner Zone of the Southwestern Japan Arc. And it would also be needed estimation of equivalency of cumulative seismic moment accumulated after the last faulting for evaluation on the non-characteristic earthquakes as Katsube et al (2017) showed on the that the Nagano Prefecture Kamishiro Fault Earthquake in 2014 occurred in according to the slip-predictable model (Shimazaki and Nakata, 1980).
4. Some advantages of seismic potential evaluation on the basis of slip-predictable model
The recent seismic potential evaluation based on the history of faulting is not always applicable for all active structures especially for broad deformations such as the mid-Niigata Prefecture Earthquake in 2004 and Iwate-Miyagi Nairiku Earthquake in 2008. On the other hand, to make clear the mean displacement rate and the upper limit of the last event age are capable for the most structures which generate vertical displacement, and furthermore to convert them from previous studies would be possible in most other cases. By accounting for these empirical facts, it would be a one of subjects in earthquake evaluation to estimate possible seismic moment by mean slip rate and age (or upper limit age) of the last event on the basis of the slip predictable model.
Please discuss.
Reference
Katsube, A. Kondo, H. and Kurosawa, H. (2017) Surface rupturing earthquakes repeated in the 300 years along the ISTL active fault system, central Japan. Geophysical Research Letters, 44, 6057-6064.
Shimazaki, K. and Nakata, T. (1980) Time-predictable recurrence model for large earthquakes. Geophysical Research Letters, 7, 279-282.