The eruptions that have taken place during the last three thousand years agree in several particulars. They either occurred suddenly, or, at any rate, were not preceded by a stage of moderate Strombolian activity; they were always accompanied by violent earthquakes; and all succeeded intervals of long repose. As the eruption of 1302 happened after at least a thousand years of rest, the lapse of six more centuries does not justify us in concluding that Epomeo is at last extinct.
We seem, on the contrary, to be drawing near another epoch of activity. During the four and a half centuries that followed the eruption of 1302, we have no record of Ischian earthquakes.[23] Then, suddenly, on the night of July 28-29, 1762, Casamicciola was visited by sixty-two shocks, some of which were very strong and damaged buildings. On March 18th, 1796, another severe shock took place, but destructive only in the neighbourhood of Casamicciola, where seven persons were killed. On February 2nd, 1828, the area of damage, though concentric with the former, enlarged its boundaries; 30 persons were killed and 50 wounded. On March 6th, 1841, and during the night of August 15-16, 1867, further shocks injured houses at Casamicciola, but without causing any loss of life. Slight tremors occurred at various dates in 1874, 1875, 1879, and 1880, leading up to the disastrous earthquakes here described, those of March 4th, 1881, when 127 persons were killed, and July 28th, 1883, which resulted in the death of 2,313 persons and the wounding of many others.
EARTHQUAKE OF MARCH 4TH, 1881.
The Ischian earthquakes have been fortunate in their investigators. In the spring of 1881, Dr. H.J. Johnston-Lavis, the chronicler for many years of Vesuvian phenomena, was residing in Naples. Impressed by a recent perusal of Mallet's report on the Neapolitan earthquake, and wishing to test the value of the methods explained in the last chapter, he crossed over to Ischia on March 5th; and to his unwearied inquiries extending over more than three weeks and lasting from thirteen to sixteen hours a day, we are indebted for most of what we know about the earthquake of 1881.
On March 4th, at 1.5 P.M., the great shock occurred abruptly, without any warning tremors. Its effects were aggravated by the faulty construction of the houses. The walls are of great thickness, loosely put together, and connected by mortar of the poorest quality. The chimneys and roofs also are massive, and the rafters are so slightly inserted in the walls that they were drawn out with the rocking of the houses. In such cases, the destruction was often so complete that no fissures were left available for measurement.
ISOSEISMAL LINES AND DISTURBED AREA.
The isoseismal lines as drawn by Dr. Johnston-Lavis are represented by the curves in Fig. 15. The isoseismal marked 1 bounds the area of complete destruction; it is about 1 mile long from east to west, 2/3 of a mile broad, and contains an area of not more than half a square mile. The next isoseismal (2) marks the area of partial, but still serious, destruction; this is nearly 2 miles long from east to west, 1¼ miles broad, and 2 square miles in area. Within the isoseismal 3, buildings were more or less slightly damaged. The course of this curve is somewhat doubtful, but, as drawn, it is about 3 miles long, 2 miles wide, and 5 square miles in area.
