Evaluation of Anchored Ship Motion Under Tsunami Attack

Ohta, Ryo (Kobe University) | Kobayashi, Eiichi (Kobe University) | Koshimura, Shunichi (Tohoku University) | Murayama, Masako (Toyama National College of Technology)


Huge earthquakes on the Nankai Trough which is located in the offshore of Shikoku island and Ki-i peninsula, Japan may occur in the coming years. Ships under tsunami attack in that bay may be uncontrollable, collision, drifting, grounding, etc. It is decided, to avoid such a dangerous situation, that mooring, arriving or leaving ships should evacuate to a safety area as soon as possible and be anchored there, (and let tsunami go away). The purpose of this paper is calculation of anchoring ships’ motions under tsunami attack using mathematical models, and therefore, discussed and evaluated for the safety guidelines. INTRODUCTION The Nankai Trough is a submarine trough located with south of Japan’s island of Honshu, extending approximately 900 km offshore along the south coastline. The trough outlines a subduction zone that is caused by subduction of the Philippine Sea Plate beneath Japan, which’s part of the Eurasian plate. Huge earthquakes have occurred at intervals of 150 years to 100 years in the trough, as shown in Figs.1-2. Moreover, it is estimated that there is a 50% probability of a tsunami being generated by an earthquake in this area in the next 30 years. Tsunamis may occur after an earthquake, and the tsunami arriving time to Osaka Bay is around 1h. Consequently, ships may begin to move uncontrollably, subjecting piers to tremendous sideways forces, and crash relentlessly against breakwaters. Ultimately, vessels are set adrift and run aground. That is a large number of important industrial facilities exist around Osaka Bay, several research projects concerning measures against tsunamis have been undertaken. The shallow Seto Inland Sea is 450 km long from east to west. Its width from south to north varies from 15 to 55 km. The average depth is 37 m and the greatest depth is 105 m.