JAPAN EARTHQUAKE 2011

Japan Earthquake 2011

Japan Earthquake 2011

Introduction

A ferocious tsunami spawned by one of the largest earthquakes ever recorded slammed Japan's eastern coast on Friday March 11, 2011 and resulted in the deaths of hundreds of people. Hours later, the tsunami hit Hawaii and warnings blanketed the Pacific, putting areas on alert as far away as South America, Canada, Alaska and the entire U.S. West Coast. In Japan, the area around a nuclear power plant in the northeast was evacuated after the reactor's cooling system failed. The earth quake had a magnitude measuring 9.0 on the Richter Scale which struck off Japan's north-east coast, about 250 miles (400km) from Tokyo at a depth of 20 miles.

Analysis

Japan is located on the eastern edge of the Eurasian Plate. The Pacific Plate, which is an oceanic plate, subducts (sinks under) the Eurasian Plate, which is a continental plate, to the east of Japan. This type of plate margin is known as a destructive plate margin. The process of subduction is not smooth. Friction causes the Pacific Plate to stick. Pressure builds and is released as an earthquake (Berke, 2010).

The location, depth, and focal mechanism of the March 11 earthquake are consistent with the event having occurred on the subduction zone plate boundary. Modeling of the rupture of this earthquake indicate that the fault moved upwards of 30-40 m, and slipped over an area approximately 300 km long (along-strike) by 150 km wide (in the down-dip direction). The rupture zone is roughly centered on the earthquake epicenter along-strike, while peak slips were up-dip of the hypocenter, towards the Japan Trench axis.

The March 11 earthquake was preceded by a series of large foreshocks over the previous two days, beginning on March 9th with a M 7.2 event approximately 40 km from the epicenter of the March 11 earthquake, and continuing with another three earthquakes greater than M 6 on the same day. The Japan Trench subduction zone has hosted nine events of magnitude 7 or greater since 1973.

The largest of these, a M 7.8 earthquake approximately 260 km to the north of the March 11 epicenter, caused 3 fatalities and almost 700 injuries in December 1994.

Losses in the Japanese Earthquake

The earthquake hit a highly populated area in terms of world standards (around 100-500 people per sq. km.), but a lowly populated area of Japan with the exception of the Sendai area. From FDMA, NPA and work of CATDAT, Earthquake-report.com and Daniell et al. (2011), the following summary has been put together. Around 35% of buildings in the area were built pre-1980, around 55% from 1981-2000 and 10% post 2001. In terms of seismic code, this means that around 65% has been built under major Japanese seismic codes (1981, 1987 etc.) and that the other 35% has been influenced in the past by seismic codes and earthquakes pre-war (1926, 1938). Most of the buildings are wooden in the affected area, with some concrete and steel buildings making up the ...