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Abstract

We investigated impact of dense seafloor observation network along the Japan trench, S-net, on tsunami generation and propagation modeling. We focused on the 2016 Mw 6.9 off-Fukushima earthquake, Japan, which generated the largest tsunami in this subduction zone after the S-net deployment. We inverted the offshore tsunami waveforms for the accurate tsunami source, and then used it in numerical tsunami simulation to clarify how well the tsunami waveforms recorded at the coastal sea-level stations can be reproduced. The results showed that the simulated tsunami waveforms matched the observations well for 90 min from the tsunami arrival time at each station, whereas the reproducibility in the temporal variation of tsunami energy over the long duration, including the decay process, varied from station to station. Because the discrepancies between the observations and calculations exceed the uncertainties due to the source estimation error, our results suggest the room for improvement in the propagation modeling. Another insight we found thanks to the offshore-data-constrained tsunami source is that the leading parts of the coastal tsunami waveforms might have non-negligible effect from the tsunami nonlinearity although they are often fed into linear tsunami inversion. This study has demonstrated that tsunami data from dense offshore network can contribute not only to accurate reproduction of targeted tsunami event, but also to the performance evaluation of the present source and propagation modeling technologies. We used offshore and coastal tsunami data provided by NIED, MLIT, GSI and JMA. This work was partially supported by JSPS KAKENHI Grant Numbers JP19H02409 and JP21K04621.