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Japan quake changed risk of future quakes: AIR study

Japan quake changed risk of future quakes: AIR study

BOSTON—Catastrophe modeling firm AIR Worldwide Corp. has released a study examining the impact of Japan's March 2011 Tohoku-Oki earthquake on the country's seismic risk landscape, determining that stress changes along various fault lines resulting from the event increased earthquake risk in some regions while reducing it in others.

Among other things, AIR said its study indicates “a large increase in the state of stress” underneath the Kanto Plain, on which Tokyo is located. The catastrophe modeler said the effects of the magnitude-9.0 Tohoku earthquake increased the 30-year probability of magnitude-6.7 or greater earthquakes in the area to between 81% and 93% from 72% in former estimates.

“AIR's analysis of the impacts of stress transfer have shown that the two most critical regions of risk that have been impacted by the Tohoku event are the Kanto Plain and, to a much lesser extent, the section of the Sagami Trough where the 1923 Kanto event took place,” the modeler said in its report.

The 1923 Kanto earthquake resulted in nearly 143,000 deaths and caused widespread property damage in the Tokyo-Yokohama area.

Looking across Japan, changes resulting from last year's Tohoku earthquake resulted in probable insured losses increasing by an average of 15% for return periods between one and 30 years, and by about 2% for return periods between 100 and 250 years, the AIR report said. Looking at the upper range of probability, the maximum change in likely insured losses for return periods up to 30 years is about 25%, AIR said.

Discussing the earthquake in March, the AIR report said, “Although damage from this event is most closely associated with the massive tsunami—which in places reached a height of more than 30 meters (98 feet) and demolished nearly all structures within its footprint—by AIR's estimate, the tsunami was responsible for only about 30% of overall insured losses from this event.”

“Shake damage was far more widespread—and it is worth remembering that shake damage would have been significant within the area subsequently impacted by the tsunami,” the report continued, adding that soil liquefaction damage stemming from the earthquake also was substantial, particularly in the Tokyo Bay area.

The new AIR report can be found at