The Story of Immamura and Omori

In his 1980 presidential address to the Seismological Society of America, the great seismologist Keiiti Aki told the story of Fusakichi Omori and Akitune Immamura, and of the great Kanto earthquake of September 1, 1923.  That event destroyed the metropolis of Tokyo and killed over 130,000 persons, laying waste the cities of Tokyo and Yokohama. 

At the time of the event, Omori was considered the greatest living seismologist in Japan.  For over 17 years he had been arguing against  the younger Immamura's idea that a great earthquake would destroy Tokyo, Yokohama and surrounding regions.  Immamura had based his prediction on a kind of seismic "gap" theory, that the faults in Sagami Bay to the south of Tokyo would slip as they previously had in the 1703 Genroku and 1854 Ansei Tokai earthquakes.    Both of these shocks had magnitudes in excess of 8, and both caused widespread destruction and loss of life.

Omori believed that earthquakes never strike the same fault twice, an idea that we now know to be false.  He had argued that Immamura's ideas should be resisted as irresponsible for public safety, and sensationalist.  Immamura, on the other hand, believed that only by warning the population could risks to life and property be reduced. 

On that September day in 1923, Omori was visiting Australia to attend the Second Pan-Pacific Science Congress held in Melbourne and Sydney, Australia.  He was visiting the Riverview Observatory in Sydney when the seismographs began to record the tracings of a large and distant earthquake.  It was said that he immediately recognized that this could be the earthquake about which Immamura had given warning for all those years past.  It was such a shock that, on the voyage home to Japan, his health deteriorated sharply, and on November 8, 1923, he died shortly after his return. 

At the time of the earthquake, Immamura was sitting in his office at Tokyo University when the building began to shake.  He immediately realized that this was the major earthquake about which he had given warning.  Reporters gathered in his office soon after, and together they witnessed the effects of the fire and tsunami in which so many perished. 

Today we have possibilities never envisioned by Omori and Immamura, made possible by the internet, new data, and new models.  The calculation of hazard and risk from large earthquakes is now routine, and becomes more accurate every day as data quality improves.  As a young company, we at Open Hazards share Immamura's idea that public safety can best be served by making the best data, models, and forecasts widely available to the public.