Proceedings

2
Nov

Human-Induced Natural Disasters; We Do Not Know Our Earth

I. Towhata

Since the second half of the 20th Century, the power of human activity has increased drastically. Many big projects have been executed. As a consequence, energy consumption, material production and waste generation are profoundly greater than what they used to be 80 years ago. Moreover, human population is exploding and human habitation is spreading into regions which are not appropriate for living. Because of these situations, the risk of natural disaster is getting bigger and bigger. At the same time, people desire for safety more urgently than before. Under this circumstance, what can geotechnical experts do? We cannot stop what “nature” does but can possibly control human-induced risk. Induced earthquake is a phenomenon in which fault rupture is triggered by artificially increased shear stress or artificially reduced effective stress in potentially unstable faults. Often, reservoir water pressure and hydraulic fracturing are considered to be the major triggering mechanisms. Noteworthy is that those human activities may not necessarily be “responsible” for the disaster, although they trigger it, if the fault rupture is due within a short time. The time of rupture may be made earlier by several years in potentially unstable faults. Another natural disaster is the effect of possible global warming. This paper does not address the credibility of recent arguments on global warming. As far as the author knows, the number of rainfall-induced disaster is increasing in the recent decade. Slopes that have been stable for centuries suddenly fall down during recent rains. Such rainfall is called extreme events by experts but the problem is that they occur very often nowadays. The rising of sea level will start to threaten the human community within several decades. It seems difficult to control the temperature change soon. Then what else can we do? At least we need to mitigate the effects of heavy rain and sea level rising that are already affecting human. Probably, the final solution would be stopping big dam construction, stopping CO2 emission and giving up comfortable life that is supported by sufficient energy and goods. They are, however, difficult because of many obvious reasons. Then should we not to do anything to mitigate the risk? The basic problem is that human does not fully know the earth. In the past, several careless mistakes were made by big projects or global human activities but the present generation of human is not familiar with lessons learnt from those mistakes. Unfortunately, geotechnical engineering is not an exception. Human should establish an OPEN-ACCESS database of mistakes and failures by which natural condition and causative mechanism are easily learnt by future generations. Geotechnical database would be its essential part. It is not required to put in names of personnel concerned because giving penalty is not the aim. It is important that everybody can learn what kind of risk exist in the particular place and mitigate it.