Performance of uniform and heterogeneous slip distributions for the modeling of the November 2016 off Fukushima earthquake and tsunami, Japan

Abstract

The M w 6.9 earthquake off Fukushima Prefecture, Japan, of 22 November 2016 was followed by a tsunami that struck the Japanese coast from Hokkaido in northern Japan to Wakayama Prefecture in western Japan. We compared the performance of a seismologically deduced single-fault model, a seismologically deduced finite fault slip model (FFM), an optimized single-fault model based on tsunami data, the FFM with horizontal shift, and the tsunami waveform inversion models of the previous studies considered for this earthquake regarding reproduction of tsunami waves by tsunami computations. It is important to discuss how these models work well because it is sometimes desirable to obtain an earthquake source model to estimate tsunami waves with a simple process obtained with limited data from the viewpoint of tsunami prediction. The seismologically deduced FFM has an advantage in terms of the information of slip regions of fault plane and was superior to the seismologically deduced single-fault model, especially in predicting amplitudes of tsunami waves. This means that when only with seismic data, the FFM could narrow the range of forecast of tsunami amplitude. In the comparison of models optimized with tsunami data, the single-fault model showed the almost equivalent performance of the tsunami waveform inversion models of previous studies regarding the waveform coincidence with observations and the horizontal location at the negative peak of the initial sea surface displacement. In case the main generation region of the tsunami is concentrated in one place, the tsunamis can be expressed by a single-fault model by conducting the detailed grid search. We also confirmed that the centroid location of centroid moment tensor (CMT) solution and the absolute location of the FFM were not necessarily suitable to express tsunamis, while the moment magnitude, the focal mechanism, the centroid depth of CMT solution, and the relative slip distribution of the FFM were effective to represent tsunamis. Since this event occurred at the shallow depth, the speed of tsunami wave is particularly slow. Therefore, it would be advisable to pay attention to the horizontal uncertainty to apply seismologically obtained solution to tsunami forecast, especially when a tsunami occurs in shallow water.

Improving the Constraint on theMw7.1 2016 Off‐Fukushima Shallow Normal‐Faulting Earthquake With the High Azimuthal Coverage Tsunami Data From the S‐Net Wide and Dense Network: Implication for the Stress Regime in the Tohoku Overriding Plate

“…The subsidence peak of our model was located ∼10 km southeast and east of the models by Gusman et al (2017) and Adriano et al (2018), respectively (Figures S3a and S3b). The peak location of the model of Nakata et al (2019) was located ∼10 km northwest of our models (Figure S3c), which was estimated by horizontally shifting the location of the slip distribution model from the teleseismic data estimated by JMA (shown later, in Section 5.2) to fit the coastal tide gauge waveforms. One reason for these differences may be the assumption of the fault geometry, but the more significant reason should be the station coverage and the source-station distance.…”

“…The slip models of the mainshock and postseismic slip of Iinuma et al (2012Iinuma et al ( , 2016 and Tomita et al (2020) were provided by the corresponding authors of each article, Takeshi Iinuma and Fumiaki Tomita. The slip distribution models of Gusman et al (2017), Adriano et al (2018), andNakata et al (2019) are available in each paper. The finite fault model using the teleseismic data by JMA is shown in https://www.data.…”

“…(2018), and Nakata et al. (2019) are available in each paper. The finite fault model using the teleseismic data by JMA is shown in https://www.data.jma.go.jp/svd/eqev/data/sourceprocess/event/2016112205594689far.pdf (in Japanese, accessed on July 21, 2021) and its digital data is available from https://www.data.jma.go.jp/svd/eqev/data/sourceprocess/data/2016112205594689far.zip (accessed on July 21, 2021).…”

Rapid estimation of tsunami earthquake magnitudes at local distance

“…We calculated tsunami height from a fault model with a uniform slip. A fault of length 71 km, width 35 km, and slip 2.1 m ( M w 7.3) was assumed following a uniform-slip fault model used by Nakata et al (2019). Strike N188 • E, dip 45 • , rake 90 • , top depth 2.4 km, and a fault corner location at 38.5 • N, 143.8 • E were used as fault parameters.…”

Review on Recent Progress in Near-Field Tsunami Forecasting Using Offshore Tsunami Measurements: Source Inversion and Data Assimilation

“…Since the W-phase solution is based on a point-source model, there exists uncertainty in producing a finite-size source model from the solution, whereas the source extent can affect the resulting tsunamis along the near-field coasts. Another possible approach is to use seismic-waveform inversion to estimate fault-slip distribution (i.e., finite-fault model) for tsunami forecasting (Nakata et al, 2019), while Cienfuegos et al (2018) pointed out that there may be a large uncertainty in near-field tsunami forecasting based on the seismic-based slip distribution, especially for tsunami run-up height and inundation area. Additionally, some tsunamis are generated by non-seismic origins (e.g., landslides, volcanic eruptions), which accounts for 20% of the total tsunami events (Bernard & Titov, 2015), making it difficult to forecast tsunamis using traditional methods.…”