On proper time of the source of a strong earthquake

The physics of earthquakes was contriubuted to by the concept of proper time of the source of a strong earthquake, which is different from universal (calendar) time. The earlier idea of proper time was implicit and has been considered only in relation to the physics of aftershocks. The present paper extends the applicability of the concept of proper time, proposes a possible way of its measuring, and provides an example to illustrate the procedure for sequen-tial ordering of earthquakes by proper time. The object of this study is a global activity of strong (M & GE;7) earthquakes. We consider the sequence of earthquakes as a Poisson-type random process. Comparatively weak earthquakes are used as the "underground clock", the tick of which marks the proper time. The Poisson distribution is compared with the distri-butions for two sequences of strong earthquakes. One of the sequences is ordered by universal time, and another - by proper time. The studies indicate the distribution of events ordered by proper time is closer to the Poisson distribution than that of events ordered by universal time. We attribute this to the non-stationarity of the geological medium, which is an immanent property of the Earth's lithosphere.