Page:Great Neapolitan Earthquake of 1857 Vol 2.djvu/423

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It is barely within the limits of probability, that two shocks shall arrive at the one spot, with such coincidence in time, that the opposite semiphases of the two respective waves, shall partly or wholly neutralize each other; but it is a different affair, and of much simpler conditions, that two or more separate waves should simultaneously arrive at the one spot, i.e., should overtake or intersect at it.

There is no doubt that this actually did occur at Montemurro, at Marsico Nuovo, and at Vignola, where the conditions producing it will be evident, from Map A; and most probably it took place also, to some extent, at Avigliano, and the cities of the Melfi group, and possibly also at Canosa.

Much pains has been devoted by earthquake describers, (Hamilton, Dolomieu, Spallanzani, and others,) to the question whether towns situated upon the plain on loose