Correlation of frontal prism structures and slope failures near the trench axis with shallow megathrust slip at the Japan Trench

Yasuyuki Nakamura,Shuichi Kodaira,Koichiro Obana,Toshiya Fujiwara,Seiichi Miura

doi:10.1038/s41598-020-68449-6

Yasuyuki Nakamura, Shuichi Kodaira + Show 3 more

Open Access

https://doi.org/10.1038/s41598-020-68449-6

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Abstract

Since the giant 2011 Tohoku earthquake and tsunami, much research has focused on the distribution of coseismic slip at shallow depths during this subduction megathrust event. Here we present seismic images obtained in the immediate vicinity of the trench axis, that show thrust faults and fold-and-thrust type deformation structures near the epicenter of the 2011 Tohoku earthquake where the large coseismic slip has been inferred, and chaotic structure and the absence of thrust faults in northern and southern source areas. Seismic profiles show evidence of slope failures of the trench inner wall in a proposed tsunami source region around 39°–40° N, where the slips estimated from previous studies are in disagreement. Our results show that structural characteristics in the trench axis may be related to the occurrence of shallow megathrust slip and tsunamigenesis in the Japan Trench.

Highlights

MethodsThe seismic dataset used in this study was collected during cruise KR13-11 of R/V Kairei in 2013 and cruise KY15-14 of R/V Kaiyo in 2015
Various studies have shown that the large shallow plate boundary slip during the Tohoku earthquake occurred in the central part of the Japan Trench but did not occur in other parts
Seismic profiles near the Japan Trench axis acquired in the vicinity of the differential bathymetry estimates show that the difference in the amount of the shallow slip during the earthquake corresponds to different characteristic structures in the trench axis

Summary

Methods

The seismic dataset used in this study was collected during cruise KR13-11 of R/V Kairei in 2013 and cruise KY15-14 of R/V Kaiyo in 2015. A digital streamer cable with 168–192 channel hydrophones at 6.25 m intervals, towed at 6 m depth, recorded seismic signals from an array of airguns (6.23 L) towed at 5 m depth. The data were sampled at 1 ms intervals, and airguns were fired every 37.5 m with 13.8 MPa of air pressure. We obtained the best time-migrated images from the recorded data by using conventional procedures described in Ref.[12]

Results

Discussion

Conclusion