Assessment of ship evacuations in response to pending tsunamis

Earthquakes occur due to friction between two geological plates. Historically, numerous earthquakes have occurred in the southern Sea of Japan. As of January 2008, the estimated probability of occurrence of the next Nankai or Tonankai earthquake within the next 30 years has been set at 50 or 60–70%, respectively. Should either of these earthquakes occur, a tsunami resulting in great horizontal movement and force could also result, setting numerous vessels adrift inside ports, causing destruction to port facilities, and endangering human life inside the vessels. Thus, appropriate countermeasures are required for ships because they may be forced to change locations unexpectedly. To minimize the probability of disaster should a tsunami forecast be issued, all vessels in Osaka Bay will need to evacuate immediately and proceed to safe anchorage areas before the tsunami arrives. However, the orderly evacuation of ships to safe anchorage areas would face difficulties due to traffic density within the Osaka Port area, and so appropriate improvements to ship traffic management are required. In this paper, several vessel-related issues, such as inter-ship distances, evacuation order procedures prior to the arrival of the first tsunami, and the first peak tsunami arrival time, are evaluated using general discrete event simulation.