The West Japan Heavy Rain Disaster at the beginning of July (2018) came as quite a shock. In response, I am going to cut back the contents I meant to talk about to a few words at the close and begin by talking instead about this rain disaster.
　　Developing out of Typhoon No. 7 (“Typhoon Prapiroon”) at the end of June, a “linear precipitation zone” of a type not previously familiar passed over Western Japan from Saga Prefecture on July 7 to Gifu Prefecture on July 9 causing widespread heavy rain damage. In addition to the wide extent of the damage, the sheer amount of continuous heavy rain from July 6 to July 8 (three-day totals in excess of 500 mm, with extremes of over 1800 mm in parts of Ehime and Kochi) set new records virtually everywhere.
　　More than 220 human lives were lost, many of them victims of rockslides in decomposed granite mountainside zones. But in addition, it is worth remembering that these deaths also included: ① more than 50 from river water floods in the Mabi district of Kurashiki where the Oda and several other tributaries of the Takahashi River broke their embankments to create conditions which it is hard to know whether to describe better as outflow (river flooding) or inflow (overland flooding); ② at least 23 following the overflow and then failure of a debris flow containment dam in Hiroshima Prefecture; ③ 5 resulting from an operating “mistake” at a dam in Ehime Prefecture.
　　Let me add that the Ministry of Land and Transport has since posted a short 15-minute video on YouTube showing the results of a detailed simulation of the river flooding (outflow) that would result from three days of continuous rain exceeding 500mm in total in the Chichibu area of Saitama around the upper reaches of the Arakawa River that flows into Tokyo.
　　There is no reason to suppose that conditions with the same novel characteristics as the West Japan Heavy Rain Disaster (widespread continuous rainfall in vast amounts) could not strike Tokyo, Osaka, Nagoya, or other large conurbations. We often hear lately that the sewers, subsurface dams, underground transport networks and so on in large cities are now securely safeguarded against inflow-type overland flooding. But it is much rarer to hear that much progress has been made in ground improvements, super-embankments and similar safeguards against outflow-type river flooding.
　　Massive rainfall is not our only worry. Tokyo, and the other large conurbations, are perfect targets for direct epicentral earthquake strikes or offshore trough earthquakes. Long-period / long-duration seismic movements striking sedimentary basins can cause huge ground disturbances in soft clay areas that were supposed to be “proof” against earthquakes. “The embankments on soft clay grounds in large conurbations are at risk.” This is an issue that has shown up time and again in calculations performed with GEOASIA software. In the three main conurbations named above, there are a total of more than 4 million people living in extensive zones zero meters above sea level. What would become of them if an earthquake were to destroy a seawall embankment and let in the ocean? The fatality numbers that come to mind run far in excess of 200. It makes one quite gloomy to think how frail and exposed our big cities are against external forces of nature such as earthquakes or extreme rainfall. Looking at the images of the heavy rain disaster, the two thoughts that came home forcefully to me were, first: “The basic key to disaster prevention is in hardware,” and then second: “GEOASIA has so much to offer to the technologies for ground improvement and embankment reinforcement; if only we could make this even more widely known.”
　　Work pursued in the GEOASIA Research Society in recent years has been concentrated especially on the theoretical side, including notably: ① a more deeply penetrating version of the combined loading model for the finer description of dynamic characteristics in sandy soils; ② enhancement of the 3-phase soil skeleton -water- air analysis; and further, ③ elaboration of the theory for a Full Formulation description of a multi-phase mixture, with means for overcoming impediments to computation. While excellent progress has been made in each of these several projects, the steady improvements thus achieved in geo-mechanical theory and the accuracy of calculations also gives rise to situations in which particular research objectives become hard to reconcile with the more ongoing aim of “spreading the use of GEOASIA”. In the coming year, we hope to be able to report a more satisfactory solution to this conflict.

Akira Asaoka
Senior research advisor, the Association for the Development of Earthquake Prediction (reg. foundation);
Emeritus professor, Nagoya University