Other effects, such as foundation instability, could not account for the widespread destruction and the subsequent abandonment of a large part of the city. An unrecorded earthquake is the only possibility. In light of the recent earthquake, the official map of seismic risk in Greece will probably be slightly modified. Yet, this modified map will be based on the same principles and techniques as the current one, and it will share the same weaknesses. Seismic maps are used for estimating seismic risk, setting building code standards, and for predicting the likelihood of earthquakes.
Earthquakes are unpredictable, however.
The Grevena earthquake proves that a lack of fatalities does not necessarily suggest weak earthquake magnitude. This is an important consideration to keep in mind when evaluating the 2500-year record of seismicity in Greece and other areas. In some parts of Greece major earthquakes strike previously seismic areas within some tens or hundreds of years and can be described by conventional seismological methods. In other areas, however, earthquakes are very infrequent, and the above methods are not useful for estimating risk. Or, even worse for calculating earthquake risk, the distribution of seismicity in time is not uniform, and periods of high seismicity alternate with quiescent periods.