AIR updates Japan earthquake model

Catastrophe modelling firm AIR Worldwide has updated its earthquake model for Japan to include insights gained from the Great Tohoku earthquake of March 2011.

The Tohoku earthquake yielded a vast amount of ground motion data, damage observations, and detailed claims data. In addition to capturing the complex seismicity of Japan and the changes that took place as a result of the Tohoku event, AIR said the updated model incorporates losses due to tsunami and liquefaction as well as ground shaking and fire following the event.

"AIR seismologists undertook an intensive re-examination of information from various sources, including physical and statistical models that calculate how the Tohoku rupture affected stress accumulation on nearby faults," said Dr Jayanta Guin, senior vice president of research and modelling at AIR Worldwide.

"The Tohoku event had important implications for our understanding of seismic risk in Japan and has also highlighted the importance of explicitly modelling earthquake-associated perils like tsunami and liquefaction."

The updated earthquake model features an improved understanding of the seismicity on the Kanto Plain, home to some of the largest concentrations of exposure, including Tokyo. The new model also reflects a more thorough understanding of subduction zone segmentation and the possibility of multisegment ruptures as well as a new formulation of plate geometry where the Pacific and Philippine plates interface beneath the Kanto Plain.

"Going far beyond simply revising rupture occurrence probabilities in the existing model, AIR's updated model reflects a new understanding of the complex network of plate boundaries and crustal faults that underlie the Japanese archipelago," said Guin.

Using extensive claims data following the Tohoku earthquake, AIR has also taken a new look at damage functions across all lines of business, including personal accident, marine hull and cargo, and complex industrial facilities.

Separate damage functions for all four earthquake perils (shake, tsunami, liquefaction, fire following the event) have been validated against a substantial amount of individual claims from the Tohoku event. Most notably, this claims data revealed wood construction to be more vulnerable than previously considered. Because a vast majority of residential structures are wood, this insight has a significant impact on Japan's risk profile.

"The Tohoku earthquake triggered new research in the seismological community, which AIR has closely followed," concluded Guin. "This update incorporates those new findings into a robust, scientifically sound, and extensively validated model, providing clients with a forward-looking view of earthquake risk assessment in Japan."