school energy&environment

Is a forecast possible?

Apart from the forecasts that can be made on the basis of statistics, the analysis of events that took place in history, have shown that the movements that generate an earthquake usually are not sudden, but are preceded by a series of premonitory signs, and if these are noted in time, they can help to foresee the onset of the event. Unfortunately, however, these signals are often feeble and can only be recorded instrumentally, and often they are hardly noted. Furthermore none of these can exactly forecast the date and time of an earthquake, which makes it very difficult to programme the alarms and the necessary evacuation of the population, sometimes even many months before the event. Quite often cases of alarms given immediately, perhaps too early, were later withdrawn because they were apparently without foundation, and were then followed by the pre-announced seismic event. At times the uncertainty of the forecast is considered a negative forecast, in a field in which a conditional response is a must, just as it should be for patience. In fact which one of us would be ready to abandon his home and job for a few months because “perhaps” there could be an earthquake in the vicinity?
Among the more common premonitory signs, which are also the most confirmed signs, there is an increase in the low intensity earthquakes, the so-called microseisms, that can only be recorded instrumentally, accompanied by deformations in the crust, the opening of small fractures, movements along the faults at times marked by an increase in the number of small landslides, some variations in the property of rocks, such as an increase in electric conductivity due to the formation of microfractures, the liberation of particular gases such as radon, caused by the microfractures, the increase in the level of the water table, that is easy to monitor by checking the water levels in the wells. The problem is that often these phenomena do not occur together and they almost never are of an intensity that is high enough to attract attention, and even worse, many very intense seisms occur without even one truly apparent precursory symptom. Many animals, and at times, some people, are able to feel the nearing of an earthquake, probably because they are sensitive to the variations in the electromagnetic field that precede an earthquake, or because they can hear the infrasounds that are tied to the propagation of seismic waves. Here, though, we are entering the field of “premonitory signs” more than forecasts, therefore, if no instrumental monitoring systems are present, it is difficult to rely on the state of agitation of Fido the pet dog or of the fish in the garden pond: it is difficult to analyze whether it is all due to the nearing of an earthquake or only because of a wandering kitten in the neighbourhood.
Therefore it is quite difficult to make accurate forecasts, specially in precise terms of hours or days. In China, one of the greatest earthquakes ever registered was forecasted 5 years before, however this was not sufficient to save the 250,000 persons who lost their lives, perhaps because of the long, excessive lapse of time between the alarm and the event.