by Viktor MORGUNOV, Dr. Sc. (Phys. & Math.), Joint Institute of Earth Physics named after O. Schmidt, RAS
When can we expect the next earthquake to strike? Questions of this kind are not mere curiosity for the residents of tremor-prone regions, to say nothing of expert seismologists. The problem of earthquake prognostication has been a matter of priority for geophysicists for more than a century. Its practical importance continues to grow with the growth of megalopolises and what are called ecologically hazardous technologies.
HOPES AND REALITY
According to time scale, experts distinguish three types of quake forecasts: long-term (tens and hundreds of years), medium (several months) and short-term (days and hours).
In ancient times people learned to identify the signs, or harbingers, of an approaching "doom", such as changing water levels in wells, new springs gushing up, and others running out of water, strange behavior of domestic animals and night-time glow of the sky... Such signs and phenomena cannot be simply shrugged off as legends or freaks of imagination and this is especially so in the light of modern instrumental data. And the list of the usual "omens" today includes computer failures, radio and TV interferences, and/or upsets in power grids such as those caused by major magnetic storms. This being so, we still cannot fully rely upon such omens and forebodings, which means that in our modern day and age earthquakes mostly remain as unpredictable as centuries ago.
On the more optimistic side, however, experts have been able to cope with the task of what they call seismic zoning * , which simply means long-term prognostication. Detailed maps with "diagrams of probability" of tremors of different strength are an indispensable "foundation" of all major building projects now. But having this "safety warranty" alone is not enough for the prevention of often tragic aftermaths of tremors. This underlines the importance of short-term prognostication.
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