It is well known that large earthquakes are accompanied by a series of smaller shocks. The characteristics of these series depend on the magnitude and focal mechanism of the main event. The relation between the main shock and the following aftershocks is well known from the study of many series of earthquakes, in such a way that the study of these phenomena may be the basis to study the mechanism of earthquake activity in a given area.

In the present study the main shock of the series detected in the Andean Valley of Zongo the first of April 1967, had a magnitude of 4.6 in the unified magnitude scale of Richter. This shock was preceded by three foreshocks and followed by at least sixteen small aftershocks.

The analysis of the time distribution of the events and their relative magnitude indicates a rather small number of minor magnitude events, indicating that the status of equilibrium of the region was reached almost completely by means of the main shock. The energy associated with the main shock is about two hundred times the total energy released by all the other small events put together.

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