Advanced Real Time Monitoring System and Simulation Researches for Earthquakes and Tsunamis in Japan - Post-Tsunami Hazard: Reconstruction and Restoration - page 174

important in the disaster mitigation programs and related measures. Real-time
monitoring data should be integrated with the advanced simulations for precise
earthquake and/or tsunami early warnings and rapid estimation of the damages.

Keywords DONET ￿ Real time monitoring ￿ Simulation ￿ Nankai trough

12.1 Introduction

The one of lessons learned from the 2011 East Japan Earthquake is the importance
of real time monitoring for earthquakes and tsunamis. Especially, offshore monitor-
ing is indispensable for the earthquake and tsunami early warnings. Actually, two
cabled pressure gauges at offshore detected the 2011 large tsunami offshore in
advance. From these observations, tsunami heights were estimated over 5 m.
Consequently, these tsunami detections in advance were successfully used to up-
grade tsunami warning level from 3 m to 6 m immediately. The ocean-bottom data
are also needed in estimation for the recurrence cycle of mega thrust earthquakes
and tsunamis. In the previous simulation researches, the result of recurrence cycle
simulation indicated the difference patterns and intervals of mega-thrust earthquake
recurrences in each cycle (e.g. Kodaira et al. 2006 ; Ohtani et al. 2014 ). These results
were consistent with the recent historical earthquakes in 1854, 1944/1946 and 1707
around the Nankai trough. In the past two historical events, fi rst ruptures were start-
ing from the Tonankai seismogenic zone. Therefore, real-time monitoring of the
Tonankai seismogenic zone is expected to improve accuracy of the recurrence cycle
simulation to understand the system of mega thrust earthquakes around the Nankai
trough. We accordingly deployed DONET1 as a real-time monitoring system focus-
ing on the Tonankai seismogenic zone (Kawaguchi et al. 2012 ; Kaneda 2013 ), and
deploying DONET2 focusing on the Nankai seismozenic zone. Also, in order to
utilize these real time data for prediction researches and disaster mitigation, we
investigate the advanced simulation using high performance computers.

12.2 Previous Studies of the Nankai Trough

Seismogenic Zone

12.2.1 Nankai Trough Seismogenic Zone

The Nankai trough seismogenic zone is one of the most important seismo-
genic zones for disaster mitigation in Japan. In the Nankai trough, M8 class
earthquakes have occurred with the intervals of 100-200 years. At the latest