Page:Great Neapolitan Earthquake of 1857 Vol 2.djvu/340

left the continuous chain of lofty mountains forming the S.W. flank of Val di Diano, and going down to Sapri and Maratea. This range, from the northern end, twelve or fifteen miles in length, opposed itself almost transversely to the wave: as the direction of the wave-paths going further south, became more oblique to the range, the effect of the latter was not only to bar the progress of the wave, across the ridge, but to conduct it "end on" along its own line, and parallel, or nearly so, to the major axis of the mezoseismal oval.

Proceeding now to the first isoseismal (— ··· — ··· —), it is crossed diagonally, by the great north and south chain, from about Avigliano on the north, to Lauria on the south; the north end curving round, from Laviano towards Potenza, so that for the most northernly portion, of about fifteen geographical miles in length, the chain presents itself transversely to the wave everywhere, and at a distance to the axis of not more than ten geographical miles.

In a word, looking broadly at the Maps A and B, it will be seen that from Oppido, to the north, all round to the westward and south-west, by Avigliano, Buccino, Castelluccio, Petina, Sassano, and Buona Bitacola, the first isoseismal, is barred in, and absolutely surrounded, (except at the narrow gap of Castelluccio, valley of the Tanagro,) by continuous transverse chains, so that the seismic vertical, stands as it were, in the focus of a great amphitheatre of mountains, which barred the progress of the wave across them, and acted like a vast elliptic reflector, to deliver back the impulse, towards the east by south.

In the direction from the focus, of east by north, (Caggiano to Potenza,) the wave progress was impeded, by the transverse action of the north and south Apennines: but

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