Presence of interplate channel layer controls of slip during and after the 2011 Tohoku-Oki earthquake through the frictional characteristics

Ryoko Nakata,Seiichi Miura,Ryota Hino,Takane Hori

doi:10.1038/s41598-021-86020-9

Ryoko Nakata, Seiichi Miura + Show 2 more

Open Access

https://doi.org/10.1038/s41598-021-86020-9

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Abstract

There are significant differences between the middle and southern segments of the Japan Trench in terms of the seismic and aseismic slips on the plate interface and seismic velocity structures. Although the large coseismic slip of the 2011 Tohoku-Oki earthquake was limited to the middle segment, the observed negative residual gravity anomaly area in the southern segment corresponds to the postseismic slip area of the Tohoku-Oki earthquake. A density distribution model can explain the different slip behaviours of the two segments by considering their structural differences. The model indicates that the plate interface in the south was covered with a thick channel layer, as indicated by seismic survey imaging, and this layer resulted in a residual gravity anomaly. Numerical simulations which assumed evident frictional heterogeneity caused by the layer in the south efficiently reproduced M9 earthquakes recurring only in the middle, followed by evident postseismic slips in the south. This study proposes that although the layer makes the megathrust less compliant to seismic slip, it promotes aseismic slips following the growth of seismic slips on the fault in an adjacent region.

Highlights

Many studies which investigated the spatiotemporal distributions of various seismic and geodetic events and underground structures have demonstrated that there are conspicuous differences between the middle and southern segments of the Japan Trench
Palaeoseismological evidence collected along the Japan Trench demonstrated that deep-sea turbidites which originated from large earthquakes potentially similar to the 2011 Tohoku-Oki earthquake are recorded only in the middle s egment[6]
Evident hollow interplate seismicity after the 2011 earthquake, which is another indicator of the coseismic slip area of the M9 earthquake[16], and past large thrust earthquakes are located outside the negative anomaly zone, whereas the distributions of postseismic slip from the Tohoku-Oki earthquake and slow earthquakes correspond to the zone[15]

Summary

Conclusions

We demonstrated that the presence of a thick, low-velocity channel layer in the subducting plate at the southern segment of the Japan Trench is consistent with gravity anomaly distribution characteristics, which accounts for the significantly different slip behaviour of the middle and southern segments near the trench axis. Gravity anomaly and seismic velocity without any significant contradictions. By representing the presence of the channel layer as the value of a characteristic slip distance in the rate- and state-dependent frictional law, we efficiently reproduced the longer duration of the postseismic slip of the 2011 Tohoku-Oki earthquake, as well. As the spatial distributions of the complementary coseismic and postseismic slips at the middle and southern segments, maintained for recurrence intervals of ~ 600 years

Method of estimation of density distribution

Method of simulating earthquake generation cycles