Comparison between earthquake generation process and local seismic process

In many cases an earthquake process can be modelled by a renawal process with mixture distributed failure time. This can be interpreted like a symptom of the presence in the process of two families of events, each with its preferred return period. Frequently this fact is associated with the bimodality of probability density function of reccurrence time. This paper shows that in general the bimodal behaviour of probability density function of recurrence time is much less evident at the site; it practically disappears when the size of seismogenetic zone is large. Moreover, a comparison is done between the local process, theoretically derived, and a local process, directly estimated from the local data are made and the diffrence are relevant.