Supercycle in great earthquake recurrence along the Japan Trench over the last 4000 years

Geoscience Letters, Apr 2018

On the landward slope of the Japan Trench, the mid-slope terrace (MST) is located at a depth of 4000–6000 m. Two piston cores from the MST were analyzed to assess the applicability of the MST for turbidite paleoseismology and to find out reliable recurrence record of the great earthquakes along the Japan Trench. The cores have preserved records of ~ 12 seismo-turbidites (event deposits) during the last 4000 years. In the upper parts of the two cores, only the following earthquakes (magnitude M ~ 8 and larger) were clearly recorded: the 2011 Tohoku, the 1896 Sanriku, the 1454 Kyotoku, and the 869 Jogan earthquake. In the lower part of the cores, turbidites were deposited alternately in the northern and southern sites during the periods between concurrent depositional events occurring at intervals of 500–900 years. Considering the characteristics of the coring sites for their sensitivity to earthquake shaking, the concurrent depositional events likely correspond to a supercycle that follows giant (M ~ 9) earthquakes along the Japan Trench. Preliminary estimations of peak ground acceleration for the historical earthquakes recorded as the turbidites imply that each rupture length of the 1454 and 869 earthquakes was over 200 km. The earthquakes related to the supercycle have occurred over at least the last 4000 years, and the cycle seems to have become slightly shorter in recent years. Earthquakes off the Sanriku coast forming the alternative deposition of turbidites in the two cores have released a part of accumulated slip, as indicated by the turbidites deposited in only one core. Decreases in the release of accumulated slip have possibly caused the recent shortening of the supercycle.

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Supercycle in great earthquake recurrence along the Japan Trench over the last 4000 years

Usami et al. Geosci. Lett. Supercycle in great earthquake recurrence along the Japan Trench over the last 4000 years Kazuko Usami 0 3 Ken Ikehara 3 Toshiya Kanamatsu 2 Cecilia M. McHugh 1 4 0 Atmosphere and Ocean Research Institute, The University of Tokyo , 5-1-5, Kashiwanoha, Kashiwa-shi, Chiba 277-8564 , Japan 1 Earth and Environmental Sciences, Queens College, City University of New York , 65-30 Kissena Boulevard, Flushing, NY 11367 , USA 2 Research and Development Center for Earthquake and Tsunami, Japan Agency for Marine-Earth Science and Technology (JAMSTEC) , 2-15 Natsushima-cho, Yokosuka 237-0061 , Japan 3 Geological Survey of Japan, National Institute of Advanced Industrial Science and Technology (AIST) , Tsukuba Central 7, 1-1-1 Higashi, Tsukuba 305-8567 , Japan 4 Marine Geology and Geophysics, Lamont-Doherty Earth Observatory of Columbia University , PO Box 1000, Palisades, NY 10964 , USA On the landward slope of the Japan Trench, the mid-slope terrace (MST) is located at a depth of 4000-6000 m. Two piston cores from the MST were analyzed to assess the applicability of the MST for turbidite paleoseismology and to find out reliable recurrence record of the great earthquakes along the Japan Trench. The cores have preserved records of ~ 12 seismo-turbidites (event deposits) during the last 4000 years. In the upper parts of the two cores, only the following earthquakes (magnitude M ~ 8 and larger) were clearly recorded: the 2011 Tohoku, the 1896 Sanriku, the 1454 Kyotoku, and the 869 Jogan earthquake. In the lower part of the cores, turbidites were deposited alternately in the northern and southern sites during the periods between concurrent depositional events occurring at intervals of 500-900 years. Considering the characteristics of the coring sites for their sensitivity to earthquake shaking, the concurrent depositional events likely correspond to a supercycle that follows giant (M ~ 9) earthquakes along the Japan Trench. Preliminary estimations of peak ground acceleration for the historical earthquakes recorded as the turbidites imply that each rupture length of the 1454 and 869 earthquakes was over 200 km. The earthquakes related to the supercycle have occurred over at least the last 4000 years, and the cycle seems to have become slightly shorter in recent years. Earthquakes off the Sanriku coast forming the alternative deposition of turbidites in the two cores have released a part of accumulated slip, as indicated by the turbidites deposited in only one core. Decreases in the release of accumulated slip have possibly caused the recent shortening of the supercycle. Japan Trench; Earthquake; Turbidite; Supercycle Background The 2011 off the Pacific coast of Tohoku earthquake (2011 Tohoku earthquake) occurred on March 11, 2011. It was an interplate earthquake that occurred along the Japan Trench with Mw 9.0 (Suzuki et  al. 2011) . This earthquake triggered huge destructive tsunamis that hit the Pacific coast of Northeast Japan, thus causing extensive damage. This earthquake forced a revision of the conventional understanding of the recurrence patterns of great earthquakes along the Japan Trench (Satake 2015) . These recurrence patterns have conventionally been studied through historical and instrumental records on the last few centuries. Therefore, the use of geological records has become more important source of long timescale evidence about the recurrence of great earthquakes. Onshore tsunami deposits provide evidence that significant earthquakes and tsunamis have impacted the Pacific coast of Tohoku in the past (Abe et  al. 1990; Minoura and Nakaya 1991; Minoura et al. 2001; Sawai et al. 2012, 2015; Ishimura and Miyauchi 2015; Takada et  al. 2016; Ishimura 2017) . Even before the 2011 Tohoku earthquake, two earthquakes along the Japan Trench (the A.D. 869 Jogan earthquake and the 1454 Kyotoku earthquake) that generated giant tsunamis similar to the one in 2011 are indicated by historical records and tsunami deposits (Satake et al. 2008; Namegaya and Yata 2014; Sawai et al. 2015) . The 1896 Sanriku earthquake known as “tsunami earthquake” also caused serious damage to the Tohoku region (Kanamori 1972; Tanioka and Satake 1996; Satake et  al. 2017) and formed tsunami depo sits (e.g., Takada et  al. 2016 ). Although tsunamis that originated at great distances have also produced some onshore deposits on the Sanriku coast (e.g., the 1960 Chilean tsunami deposits; Kon’no et  al. 1961) , the major cause of large tsunamis in this area is interplate earthquakes along the Japan Trench (Minoura and Nakaya 1991; Minoura et al. 2001; Namegaya and Satake 2014; Sawai et  al. 2015) . However, submarine landslides could also cause some large tsunamis (Tappin et  al. 2001; Kawamura et  al. 2014) . In general, it is difficult to discern the cause of a tsunami solely on the basis of the characteristics of onshore tsunami deposits. Seismo-turbidites (turbidites deposited by earthquake-trig (...truncated)


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Kazuko Usami, Ken Ikehara, Toshiya Kanamatsu, Cecilia M. McHugh. Supercycle in great earthquake recurrence along the Japan Trench over the last 4000 years, Geoscience Letters, 2018, pp. 11, Volume 5, Issue 1, DOI: 10.1186/s40562-018-0110-2