Review on near-field tsunami forecasting from offshore tsunami data and onshore GNSS data for tsunami early warning

This paper reviews recent studies on methods of realtime forecasting for near-field tsunamis that use either offshore tsunami data or onshore global navigation satellite system (GNSS) data. Tsunami early warning systems for near-field coastal communities are vital because evacuation time before tsunami arrival is usually very short. We focus on forecasting between the occurrence of a tsunamigenic earthquake and the arrival of the first tsunami at a near-field coast - typically a few tens of minutes or less after the earthquake. Offshore tsunami measurement that provides coastal communities with direct information on impending tsunamis is very effective in providing reliable tsunami predictions. Crustal deformation due to coseismic slips at an earthquake fault detected by real-time GNSS analysis is quite useful in estimating fault expansion and the amount of slip, which in turn contributes to timely tsunami warnings, e.g., within 10 minutes, even for huge interplate earthquakes. Our review encompasses methods on the leading edge of research and those already in the process of being applied practically. We also discuss an effective combination of methods developed for mitigating tsunami disasters.