The huge scale of the Great East Japan Earthquake is forcing the Japanese government to review the basic principles of its earthquake risk assessment system and may have far-reaching consequences for anti-quake measures in homes, offices and nuclear power plants across the country.
The huge scale of the Great East Japan Earthquake is forcing the Japanese government to review the basic principles of its earthquake risk assessment system and may have far-reaching consequences for anti-quake measures in homes, offices and nuclear power plants across the country.
The government's Earthquake Research Committee said on June 9 that it would re-examine its methods of estimating the likelihood and scale of future earthquakes.
The changes could mean much stronger quakes being envisaged by a system that failed to anticipate the magnitude-9.0 earthquake on March 11.
The review is likely to overhaul the forecasting of earthquakes that strike around ocean trenches and, particularly, temblors, like the Great East Japan Earthquake, that are triggered by the subduction of ocean plates under continental plates.
The committee will study evidence including sand swept inland by the March 11 tsunami and active faults along the seabed to try to get a better understanding of what happened on March 11.
Data on past earthquakes in the region will be reviewed, as well as crustal movements along the seabed.
The Great East Japan Earthquake is believed to have been the result of a series of earthquakes occurring in more than one region, and that is likely to force the committee to look at possible connections between stresses in different ocean trenches.
The committee's first goal will be to revise its assessment of earthquakes occurring off the Sanriku and Boso coasts based on data obtained from the Great East Japan Earthquake. That report is expected by about this autumn.
The committee will then review its forecasts for the Nankai trough, which could trigger earthquakes in the Tokai, Tonankai and Nankai regions. Quakes in those areas would have a major impact because they include heavily populated areas. The Nankai revision is expected by about spring 2012.
At a news conference following the June 9 meeting, committee Chairman Katsuyuki Abe, professor emeritus at the University of Tokyo, said the old system had failed to draw sufficiently on the data available. There was evidence, for instance, that a massive earthquake struck the Tohoku region in 869.
"We have to reflect on our inability to fully utilize past knowledge to forecast the Great East Japan Earthquake," Abe said. "(This review) is an expression of our resolve to include appraisal methods that have scientific basis and that can help provide a forecast for the future."
If the new forecasts predict bigger quakes, assessments of the height of tsunami and the size of areas at risk from tsunami would be increased proportionately. That would affect the location and height of breakwaters and levees in coastal areas, and force disaster management maps and evacuation plans to be redrawn. Different evacuation centers and evacuation routes would likely be chosen, and plans for dispatching police and firefighters could change.
Areas relatively distant from the ocean trenches would also be affected. A quake in the Nankai trough, for instance, could hit skyscrapers in the Tokyo, Kansai and Nagoya regions, and changes in the committee's predictions should force a reassessment of anti-quake precautions for many major buildings.
The anti-quake guidelines for the nuclear industry, revised in 2006 by the Nuclear Safety Commission of Japan, were based on quakes that had struck near nuclear power plants in the past. A change in Earthquake Research Committee methodology could force a greater emphasis on earthquakes centered on ocean trenches and a revision of the risk assessments for nuclear plants along the Pacific coast, which are vulnerable to trench earthquakes.
The Earthquake Research Committee comes under the government's Headquarters for Earthquake Research Promotion, which was established to deepen understanding of earthquakes following the Great Hanshin Earthquake of 1995.