Multi-index method using offshore ocean-bottom pressure data for real-time tsunami forecast

Abstract

We developed a real-time tsunami forecast method using only pressure data collected from the bottom of the ocean via a dense offshore observation network. The key feature of the method is rapid matching between offshore tsunami observations and pre-calculated offshore tsunami spatial distributions. We first calculate the tsunami waveforms at offshore stations and the maximum coastal tsunami heights from any possible tsunami source model and register them in the proposed Tsunami Scenario Bank (TSB). When a tsunami occurs, we use multiple indices to quickly select dozens of appropriate tsunami scenarios that can explain the offshore observations. At the same time, the maximum coastal tsunami heights coupled with the selected tsunami scenarios are forecast. We apply three indices, which are the correlation coefficient and two kinds of variance reductions normalized by the L2-norm of either the observation or calculation, to match the observed spatial distributions with the pre-calculated spatial distributions in the TSB. We examine the ability of our method to select appropriate tsunami scenarios by conducting synthetic tests using a scenario based on "pseudo-observations. " For these tests, we construct a tentative TSB, which contains tsunami waveforms at locations in the Seafloor Observation Network for Earthquakes and Tsunamis along the Japan Trench and maximum coastal tsunami heights, using about 2000 tsunami source models along the Japan Trench. Based on the test results, we confirm that the method can select appropriate tsunami scenarios within a certain precision by using the two kinds of variance reductions, which are sensitive to the tsunami size, and the correlation coefficient, which is sensitive to the tsunami source location. In this paper, we present the results and discuss the characteristics and behavior of the multi-index method. The addition of tsunami inundation components to the TSB is expected to enable the application of this method to real-time tsunami inundation forecasts in the near future.

Synthesizing ocean bottom pressure records including seismic wave and tsunami contributions: Toward realistic tests of monitoring systems

“…It mainly focused on generating a warning for the tsunamigenic earthquake that occurs at a distance from the site where the warning is issued. It is also critical to develop and examine the performance of the tsunami forecasting method for the coasts near the source where disastrous tsunami arrives within~30 min [e.g., Tsushima et al, 2009;Wei et al, 2013;Gusman et al, 2014;Maeda et al, 2015;Inazu et al, 2016;Yamamoto et al, 2016]. At present, there are not enough records which are observed at less than~100 km from the hypocenter or inside the focal area, although a few stations recorded tsunamis near the source region [e.g., Mikada et al, 2006;Maeda et al, 2011].…”

Potential deployment of offshore bottom pressure gauges and adoption of data assimilation for tsunami warning system in the western Mediterranean Sea

“…Both simulated and actual observation waveforms were used for forecast accuracy analysis in this study. To quantitatively analyze the accuracy of the forecasts, we applied a method for waveform comparisons by considering both the first-peak amplitude and the maximum amplitude of the tsunami, similar to the score of Tsushima et al (2009) and the index of VRO of Yamamoto et al (2016). Our method for waveform comparison applies the following equation:…”

Measuring offshore tsunami currents using ship navigation records

“…Although Japan already has dense offshore observatories for real-time tsunami monitoring and forecasting (Kawai et al 2013;Kaneda et al 2015;Yamamoto et al 2016), most countries, in particular developing countries, will not be able to install and maintain similar dense offshore observatories mainly for economic reasons. Hopefully, the use of the AIS data will play a role in new tsunami monitoring/forecasting methods especially for developing countries such as those in Southeast Asia and South America.…”

“…These forecast systems will be enhanced using real-time geodetic monitoring as well Wei et al 2014). Forecast methods using very dense seafloor observation networks have been also proposed independently (Maeda et al 2015;Igarashi et al 2016;Yamamoto et al 2016). These forecast systems using offshore tsunami observations will be robust and reliable.…”