Page:Great Neapolitan Earthquake of 1857 Vol 2.djvu/419

354 plains, nearest to $$a',$$ $$b',$$ and $$c',$$are exposed to dispersive waves, in new wave-paths, due to the breaking up of the direct wave at the flanks $$a\ a', b\ b'$$ &c., and those close to and upon the other flanks $$r,\ r',\ r'',$$ are affected by the direct waves, and by transversals getting more and more nearly vertical, as the distance from $$o$$ increases.

Several other subordinate complex effects, of similar irregularities of surface will occur to the reader.

These phenomena have found numerous examples in the present earthquake. To such actions, in part produced by the numerous, more or less parallel, chains of mountains, and variously transverse to the wave-paths, were due the alternations of energy, and abrupt reductions of effect, observable all through the districts to the N.W. of the focal centre. Nowhere were these more remarkable, than in the successive valleys between the branch ranges, running towards the south in a north and south direction between Riciliano and Pagano, (Maps A and B); while to similar causes (united with effects due to formation) was due, the comparative immunity of the group of towns, between Brindisi, Tricarico, and Acetura, in the N.E. middle space, between the meizoseismal and first isoseismal curves.

Laviano, Valva, and Oliveto afford examples, of the increased effects, on places situated on remote flanks, $$a\ a', b\ b'$$, &c. (Fig. 354) ; Picerno and Tito, of the disturbances of the wave-paths, by position on the near flanks, $$r\ r'$$, &c.; while the abrupt loss of energy, (beyond that due to increased distance only,) is well exemplified in the destruction of Tito at the near side, and the comparative safety of Potenza, (within five geographical miles of it in a right line,) at the remote side of the great Apennine.