Recent development for near-field tsunami forecasting based on real time GNSS and offshore tsunami data

The 2011 Tohoku earthquake and its associated tsunami clearly showed the need for an accurate tsunami early warning system. In a short time between the occurrence of earthquakes and associating tsunamis and the tsunami arrivals to near-field coastal inhabited regions, we can use many different kinds of observations for real-time tsunami forecasting. Since individual type of the observations has its advantages and disadvantages, it is strongly required to make use of multiple kinds of data for improving estimated size and arrival timing of imminent tsunamis by reinforcing one another. For example, the rapid analysis of short-period seismic wave data, such as earthquake early warning system in Japan will provide the first information on the size and location of an earthquake, helping issuing tsunami information immediately after earthquakes. Real-time GNSS data have an advantage over the short-time seismograms because robust estimations of location and dimension of coseismic faults can be derived from spatial patterns of permanent coseismic displacement measured by real-time GNSS data. It is one of the important lessons learnt from the 2011 Tohoku earthquake that estimation of reliable finite source fault models is indispensable in tsunami forecasting after massive earthquakes. Offshore measurements of coming tsunamis must be data most relevant to the arrival times and sizes of tsunamis along shorelines. However, it takes more time to obtain credible spatial distribution of tsunami wave height from the observations due to much slower propagation of tsunamis than seismic waves and deformations. In the presentation, we will introduce the current status of the real-time crustal deformation monitoring system based on the GNSS data developed by Geospatial Information Authority of Japan and Tohoku University. We also briefly introduce the real-time tsunami forecasting based on the offshore tsunami data, developed by the Meteorological Research Institute of Japan Meteorological Agency. Finally, we will discuss how the combination use of the real-time GNSS and the offshore tsunami observations improve the capability of tsunami forecasting.