We examined how an array configuration of offshore tsunami stations affects accuracies of near-field tsunami forecasts provided by a tsunami forecast method based on an inversion of the offshore tsunami data. We simulated tsunami forecast of the 2011 Tohoku earthquake assuming several array configurations. As a result, an installation of bottom-pressure gauges to the outer sea of the trench contributes to improving the forecast accuracies, as well as deployment of the gauges at the seafloor between a source and a coastal point where forecasts will be provided. We also examined how rapidly accuracies of tsunami forecasts improve when a dense offshore observation network is installed, and found that the accurate forecasts can be obtained from the data of the dense network 10-15 min earlier than from those of the existing-array configuration.
