14:00 〜 14:15
[SCG48-12] 日本海溝底海溝充填堆積物中に過去のslip-to-the trenchの痕跡は残されているか？：IODP 1010-APL2 JTRACK-Deep-time Paleoseismology
キーワード：日本海溝、巨大地震、地質記録、IODP
Short historical and even shorter instrumental records limit our perspective of earthquake maximum magnitude and recurrence, and thus are insufficient for fully characterize Earth’s complex and multiscale seismic behavior and its consequences. To fill the gap in long-term paleoseismic records of giant (Mw9-class) subduction zone earthquakes such as the 2011 Tohoku-oki earthquake, IODP Expedition 386 successfully collected 29 Giant Piston Cores (GPCs) at 15 sites, recovering up to 37.82-meter-long, continuous, upper Pleistocene to Holocene successions from 11 individual trench-fill basins. Preliminary results of Expedition 386 indicated that numerous event deposits of a few centimeters to a few meters in thickness are intercalated in the bioturbated clay and silty clay in the cores from the central to southern Japan Trench (JT). No obvious influence of sea-level fluctuation was recognized that would jeopardize the long-term paleoseismic record contained in the up to ~160-m-thick trench-fill sequence. Identical to the results from conventional coring, thick muddy event deposits are possible records of the past megathrust earthquakes along the JT.
In central JT basins, trench-fill sediment sequences are characterized by several slightly tilted prominent seismic reflections with high amplitudes in multi-channel seismic profiles. Tilts become larger with increasing subbottom depths, suggesting periodic tilting events, which were possibly generated by large coseismic slip propagation to trench (slip-to-trench) events in the past. The initial GPC-to-seismic correlation suggests that the uppermost reflector is correlative with the base of a thick turbidite bed of the 869 Jogan earthquake, which was a major earthquake event before the 2011 earthquake. However, due to the short recovery of GPCs, it is impossible to date the older hypothesized slip-to-trench events.
We proposed to drill a trench basin fill deposit in the central JT to recover the whole trench-fill sequence for dating and establishing event-stratigraphy for paleoseismologic interpretations. Based on the combination with stratigraphy and chronology of thick event deposits, interstitial-water geochemistry proxy-data for past fluid flow pulses in the cores and core-to-seismic correlation to paleo-slip-to-trench events, we would like to clarify how often the slip-to-trench events have occurred. The results of this proposed drilling will cover a time period that is several times longer than what can be obtained from GPC. D/V Chikyu is the only facility to recover ~160 m cores from the hadal JT. This will significantly advance our understanding of the recurrence pattern of giant earthquakes and earthquake-induced geohazards.
IODP 1010-APL2 proponents: Ikehara, K., Strasser, M., Nakamura, Y., Kanamatsu, T., Rasbury, T., Itaki, T., Nagahashi, Y., Johnson, J., Huang, J.-J., Bao, R., Ishizawa, T. and Moernaut, J.
In central JT basins, trench-fill sediment sequences are characterized by several slightly tilted prominent seismic reflections with high amplitudes in multi-channel seismic profiles. Tilts become larger with increasing subbottom depths, suggesting periodic tilting events, which were possibly generated by large coseismic slip propagation to trench (slip-to-trench) events in the past. The initial GPC-to-seismic correlation suggests that the uppermost reflector is correlative with the base of a thick turbidite bed of the 869 Jogan earthquake, which was a major earthquake event before the 2011 earthquake. However, due to the short recovery of GPCs, it is impossible to date the older hypothesized slip-to-trench events.
We proposed to drill a trench basin fill deposit in the central JT to recover the whole trench-fill sequence for dating and establishing event-stratigraphy for paleoseismologic interpretations. Based on the combination with stratigraphy and chronology of thick event deposits, interstitial-water geochemistry proxy-data for past fluid flow pulses in the cores and core-to-seismic correlation to paleo-slip-to-trench events, we would like to clarify how often the slip-to-trench events have occurred. The results of this proposed drilling will cover a time period that is several times longer than what can be obtained from GPC. D/V Chikyu is the only facility to recover ~160 m cores from the hadal JT. This will significantly advance our understanding of the recurrence pattern of giant earthquakes and earthquake-induced geohazards.
IODP 1010-APL2 proponents: Ikehara, K., Strasser, M., Nakamura, Y., Kanamatsu, T., Rasbury, T., Itaki, T., Nagahashi, Y., Johnson, J., Huang, J.-J., Bao, R., Ishizawa, T. and Moernaut, J.