CASE STUDY- Japanese Tsunami 2011

Nature of the hazard

• 2 days before there had been major tremors peaking 7.2 on the richter scale
• The earthquake measured 9.0 was the worlds 5th largest since 1990 and largest in Japan
• The epicentre was 24km deep 72km off the coast of Sendai
• Pacifc plate being subducted below Okhatsk plate
• Horizontal crust displacement 50m
• Sea bed raised 16m
• Ground shook for 6min
• Within 20min a huge tsunami developed
• 5wks after the region had expereinced 420 aftershocks greater than magnitude 5.0 suggesting continual large scale crust adjustment.

Factors contributing to vulnerability

• Only small earthquakes expected due to oceanic crust being very old and therefore should readily slide into mantle
• Warping of pacific plate as it got stuck causing strain to build up
• Ria coast - jagged coastline and inlets so waves are concentrated up rivers and bays
• 70% Japan in mountainous forcing urban/ industry developement into narrow, low lying coastal areas
• Soft reclaim land susceptable to landslides
• Government officials too complacent.

Impact of event

• Highest wave was 15 metres
• Erosion of beached + dunes
• Destruction of man made structures
• 95% of all vegetation destroyed
• 500km2 inundated in north-east Japan
• Sediment transported 5km inland on the Sendai plain
• Seawater remained on the surface for 2 months and salt crusts formed on the paddy fields as water slowly evaporated

Fukushima nuclear explosion

• Power supply damaged so cooling system failed, water continued to generate steam. Fuel rodes go hotter + reacted with steam to form hydrogen gas. This melted, damaging power station structure. Pressure rose till explosion. Seawater used as emergency coolant, radioactive substances escaped and fires developed.
• 80,000 people evacuated in a 12 mile…