Preface for the special issue of “New Perspective of Subduction Zone Earthquakes”

Abstract

Giant subduction zone earthquakes such as the recent2004 Sumatra and 2011 Tohoku-oki earthquakes and theiraccompanying tsunamis cause significant damage to hu-man society, and it is our earnest desire to scientificallyelucidate how they occur. In the Nankai Trough, Japan,great earthquakes and tsunamis have occurred repeatedly,and more are predicted for this site in the near future.Super-deep drilling by the drilling vessel Chikyu willenable us to directly sample seismogenic faults as well asconduct analyses, experiments, and in situ boreholemeasurements. These efforts should significantly improveour understanding of pre- and co-seismic processes ofgreat subduction zone earthquakes. The Integrated OceanDrilling Program (IODP, 2003–2012) and InternationalOcean Discovery Program (2013–2022) have decided topromote the Nankai Trough Seismogenic Zone experi-ments (NantroSEIZE) using Chikyu, although the deeptarget of the plate boundary fault has not yet been reachedas of 2015.We created a Japanese partnership program withNantroSEIZE (new perspective on great subductionzone earthquakes from super deep drilling: Kakenhi forthe Nankai trough megaquakes, KANAME program, withfinancial support from the Ministry of Education, Culture,Sports, Science, and Technology from 2008–2015). Thescientific objective of the program is to improve ourunderstanding of pre- and co-seismic processes of greatsubduction zone earthquakes by directly sampling seis-mogenic faults and conducting analyses, experiments,and in situ borehole measurements in the NankaiTrough region. To realize this goal, our strategy con-sists of the following three schemes: (1) understandingthe overall framework of the Nankai Trough seismo-genic zone, (2) revealing the materials and mechanicaland hydrologic properties of seismogenic faults, and (3)construction and verification of a comprehensive modelfor pre- and co-seismic processes.On March 11, 2011, during the middle phase of theKANAME program, the Tohoku-oki earthquake andtsunami took place. Chikyu was damaged by the tsu-nami in the Hachinohe harbor in northeast Japan, andall programs that had been planned for implementationusing Chikyu had to be delayed or canceled, includingNantroSEIZE and KANAME. On the other hand, IODPimmediately planned and conducted drilling at theJapanTrench,atthesiteofthe Tohoku-oki earthquake,after Chikyu was repaired. We modified the KANAMEproject to include research on the Japan Trench anddrilling at other subduction zones, such as Costa Rica.Many new findings and papers have been produced as aresult of the KANAME project. The project was com-pleted in 2015, but the NantroSEIZE effort is ongoing.This special issue presents some of the results of theKANAME project, mainly by scientists who took part inthe project, although many papers have already publishedin other journals. Drs. Shelly and Rowe were invited asguest editors in addition to our internal guest editors(Kimura, Kinoshita, and Ashi).This issue includes 33 papers:(1)The Nankai trough (14 papers; Sugihara et al. 2014,Yamano et al. 2014, Tsuji et al. 2014, Idehara et al.2014,AkuharaandMochizuki2014, Hyodo et al.2014, Ashi et al. 2014,Tanikawa et al. 2014,Takahashiet al. 2014, Yamada and Shibanuma 2015,Hamadaet al. 2015,Takeshita et al. 2014,Hinoetal.2015,andToki et al. 2014)(2)The Japan trench (6 papers; Aochi and Ide 2014,Nakamura et al. 2014, Koge et al. 2014, Lin et al.2014, Sawai et al. 2014, and Boston et al. 2014)(3)Other trenches and fault zones (4 papers; Maekawaet al. 2014,Namikietal.2014,Ishikawaetal.2014,and Yabe et al. 2014) and ancient accretionarycomplexes and faults on land (7 papers; Schumannet al. 2014, Hamahashi et al. 2015, Fukuchi et al. 2014,