Early Forecast of Long-Period Ground Motions via Data Assimilation of Observed Ground Motions and Wave Propagation Simulations

We propose an efficient approach for the early forecast of long-period (> 3-10s) ground motions generated in sedimentary basins by large earthquakes based on the data assimilation of observed ground motions and finite-difference method simulations of seismic wave propagation in a 3-D heterogeneous structure. This approach uses the dense K-NET and KiK-net nationwide networks in Japan and a high-performance supercomputer to perform forecasts using the assimilated wavefields at speeds much faster than the actual wave propagation speed. Therefore, an early alert can be issued prior to the occurrence of strong motions in basins due to large, distant earthquakes. We validated the effectiveness of this data-assimilation-based forecast approach via numerical tests for the early forecast of long-period ground motions in central Tokyo using the observed waveform data from the Mw6.6 2007 Off Niigata and Mw9.0 2011 Off Tohoku earthquakes. Plain Language Summary Large and lengthy long-period (LP) ground motions generated in large basins during large earthquakes create a potential risk of damage in modern cities resulting from heavy shaking in high-rise buildings, long bridges, oil-storage tanks, and so on. Our paper proposes an efficient approach to forecast LP ground motions caused by distant, large earthquakes. This approach monitors the generation of LP ground motions from large earthquakes via the dense strong-motion networks across Japan. Then, the future propagation and amplification of LP ground motions in distant basins are forecasted using a supercomputer at speeds much faster than the actual wave speed. In this paper we demonstrates the forecasts test of LP ground motions in central Tokyo using real seismograph records from the Mw6.6 2007 Off Niigata and Mw9.0 2011 Off Tohoku earthquakes.