Great Neapolitan Earthquake of 1857/Part II. Ch. I
CHAPTER I.
THE REGION OF OBSERVATION—ITS SEISMIC HISTORY—OBSERVATIONS AT AND AROUND NAPLES.
The seismic region to which this Report refers reaches in its most extended sense from Rome to Otranto, in a west and east direction, and from Gargano to Reggio in that north and south; since within the whole of this surface—in fact, over the whole of the peninsula south of the parallel of 42°—was the earthquake of the 16th December, 1857, more or less perceptible. In the more restricted sense, however, in which the seismic area is limited by the effects of the shocks having been forced upon the attention of the inhabitants, and left tangible traces of their advent, and thus determined the scope of the writer's observations and inquiries, it may be said loosely, to be bounded by a line stretching eastward from Sermoneta, at the head of the Pontine Marshes, to Foggia in Capitanata, and thence to the Adriatic; and comprehending all south of that, excepting the peninsula of Otranto, east of a line between Monopoli and Taranto and the peninsula of Calabria Ultra, south of a line from Cape Suvero to Cape Colonna, thus embracing the surface between lat. 39° and 41° 30' and from long. E. 10° 30' to long. E. 15° or more than 200 English miles by above 160.
This region forms part of the great seismic zone of the Mediterranean, stretching westward along the Atlas chain to the Azores, and eastward through Dalmatia, Albania, the Greek Archipelago, to Smyrna and Constantinople, and into Asia Minor, whence it bifurcates into the separate systems of Syria on the south and of the Caucasus on the north, and is one of almost constant disturbance.
Its evil celebrity has become popular through the terrible earthquake of Calabria in 1783; but the frequency and extent of its earthquakes are but little known generally.
Besides innumerable minor shocks at various points, and extending to greater or less areas, earthquakes are on record as having occurred within it in the following series of years, all of which have been of power sufficient to overthrow towns and destroy numbers of human beings, namely, in A.D.
| 1181 | 1509 | 1602 | 1654 | 1702 | 1770 | 1826 |
| 1230 | 1523 | 1609 | 1659 | 1703 | 1777 | 1832 |
| 1282 | 1537 | 1614 | 1660 | 1706 | 1782 | 1835 |
| 1343 | 1544 | 1617 | 1662 | 1731 | 1783 | 1836 |
| 1349 | 1549 | 1620 | 1670 | 1732 | 1784 | 1841 |
| 1446 | 1550 | 1623 | 1683 | 1743 | 1789 | 1847 |
| 1448 | 1551 | 1626 | 1685 | 1744 | 1805 | 1851 |
| 1450 | 1559 | 1638 | 1687 | 1746 | 1806 | 1854 |
| 1454 | 1561 | 1640 | 1688 | 1753 | 1807 | 1856 |
| 1456 | 1594 | 1644 | 1693 | 1756 | 1812 | 1857 |
| 1460 | 1596 | 1646 | 1694 | 1759 | 1814 | |
| 1486 | 1599 | 1652 | 1697 | 1767 | 1818 |
or 82 great earthquakes since the commencement of the twelfth century.
Most of these are recorded in the Catalogues of Perrey, and in the General Earthquake Catalogue of the British Association; but the particulars of many are only to be found in the works of local authors, such as Colosimo, Onofrio, Grimaldi, Lombardi, Battista, Don Arabia, Colletta, &c., which are scarce and not to be consulted collectively out of Naples.
As observed in all habitual seismic regions, the great shock of December, 1857, was preluded by several minor ones. In 1856 shocks are recorded by Perrey ('Catal. Ann.') in January, March, May, August, October, and November, some of which embraced areas extending simultaneously to Naples, Melfi, and Cosenza; and fully an equal number are said to have marked the succeeding year prior to December: the most important in either year, was felt chiefly at and around Salerno on the 12th Oct. 1856, and seems to have escaped the usually extensive information of Perrey. The following notice of it occurred in the 'Times' of 16th Oct. 1856—
"Earthquake at Sorrento, Oct. 12.—The following account of an earthquake at Sorrento is given by a correspondent:—'A few hours ago we experienced two shocks of earthquake more severe than have been felt in these regions for several years. A few minutes after two o'clock A. M. I was awakened by a sensation as if my bed were about to slide out of the window in front of me. From previous experience I instantly became aware of what was taking place, and lost no time in collecting my family in the doorways of the sleeping-rooms, which are supported by very thick walls. The oscillations continued in rhythmical intervals of three seconds until I had counted four of them. After a state of quiescence—it might have been three minutes—the house began to reel confusedly, and then composed itself into another series of pendulum-like oscillations, in a direction from east to west, more prolonged than the former. I noticed that I could count, with moderate haste, three for the advance movement, and three for the return. These were repeated five times, and accompanied by a rushing noise, as of a brewing storm, and an underground rumbling like distant thunder. Indoors the sounds resembled the straining timbers of a ship in a gale. The moon was shining serenely, and the column of white vapour was issuing from the summit of Vesuvius calmly as usual, but the hurried prayers and sobbing ejaculations of the peasants in a neighbouring podere (farmstead), and the frightened baying of the watchdogs in the orange gardens, gave evidence of the terror which had just passed over the plain of Sorrento. By some the visitation had been expected. The weather had been very sultry for several days, and a peculiarly dense and ill-smelling fog had obscured the bay. The general alarm was very great, and most of the inhabitants of Sorrento rushed into the streets and open spaces. I have not heard that damage was done to any of the houses.'"
The very day preceding this, 15th Dec. 1857, a severe shock was felt at Rhodes, indicating that very distant points in the same seismic zone were then in agitation.
In recording from my note-books, &c., the facts ascertained, I shall now, for convenience, adopt the personal pronoun.
The preliminary inquiry of a day or two at Naples decided the general plan of investigation to be pursued. I proposed to myself to search the heart of the shaken country from the westward, then to pursue a southern track until I should have nearly reached its confines in that direction, and then (by another road, and further eastward if possible,) retrace my steps, and pursue a northern course until I reached its northern confines.
I reserved for the results of so much of my examination, the determination of whether to pursue a direct eastern course, then from the middle region, or to stretch farther north, and then observe the effects of the transverse chain of the Apennines upon the main earth-wave.
Much interest attaching to the question of a permanent rise or fall in the level of the land, at or after the shock, I made such observations as were practicable at and around Naples; but none of these proving decisive, I resolved, before turning to the eastward along the course of the Salaris, to go a little further south, and examine the coast and river mouths between Naples and the mouth of the Salaris and down to Pæstum for evidences of any such movement.
The narrative, therefore, will be given in the order nearly of the places visited, condensing together observations, &c., made at different times when the same places were visited twice.
Naples, City.—The following is the official notice of the shock, translated from the 'Giornale Reale' of 17th Dec. 1857:—"We have received the following letter from the director of the Astronomical Observatory at Capodimonte—'Sir—I hasten to inform you that last night at ten minutes after ten o'clock (tempo meridiano) a shock of earthquake occurred which lasted about four or five seconds; two minutes afterwards another shock of much greater intensity occurred, which lasted about twenty-five seconds. They were both undulatory, and proceeded from the south to the north. The severity of the second shock was apparent from the fact, that two pendulum clocks belonging to this Observatory which oscillated in the plane of the prime vertical, were stopped, (three others, however, were unaffected). The foundation of the tower in which our equatorial instrument is placed also sustained injury. We were also sensible of three successive but slight shocks, at three and at five o'clock in the morning (i. e. of the 17th.’”) (See Appendix, No. 3.)
On visiting the Observatory I was unable to converse with the astronomer, Signor de Gasparis, who was unwell, but was shown over the establishment and my inquiries answered, by Signor Nobili, filio.
In the transit room (Fig. 111) ( being the two instruments), are two clocks, , whose pendulums vibrated in the plane of the prime vertical, and showing sidereal time. These were both stopped, but, according to Signor de Gasparis, at different moments, and each at an unequal period after the shock, owing to their structure, so that nothing could be concluded as to the precise moment of the first shock from them. I could not ascertain upon what precise data the moment stated in the Giornale as above, for the occurrence of the shock was based, and from other facts entertain some doubts as to its precision.
I found by measurements that a moment in the line of the meridian, and therefore transverse to the plane of vibration of less than 0.5 inch would have been sufficient to have stopped either of these clocks, unless the contact with the case and pendulum so produced, had been instantly removed by a movement in the opposite direction, and before time were given to destroy by friction the momentum of the pendulum.
In the Salle Centrale, which is also the library of the Observatory, and leads by a winding stone staircase at one end, to the top of the tower where the equatorial is fixed, is a third clock, showing Naples mean time, whose pendulum, an extremely heavy one, oscillates in the plane of the meridian, which was not stopped. A movement of the pendulum bob of 0.625 inch transverse to the plane of oscillation would have stopped this clock.
These clocks are not screwed to the walls, and neither they nor any of the other instruments had suffered damage or derangement.
Two chronometers lent by the Lords of the Admiralty, and brought with me from England, going Greenwich mean time, were compared with the time at the Observatory, and one was found to have been slightly deranged by the railway journey. I had deemed it probable, that by the co-operation of some Neapolitan savant, I should be able to get measures of horizontal surface transit velocity of the earth-wave, in some of the slight shocks said to be still continuing. The uncertainty of their recurrence and difficulties as to finding any Neapolitan co-observer, rendered this impracticable. The chronometers were, however, of much service to me in the interior of the country, one of them having been adjusted to Naples mean solar time before I started.
The Salle Centrale has its length in the direction of the meridian. At one end a doorway, (Fig. 112) leads to a stone winding staircase, descending one deep story, and ascending to the equatorial, which is thus placed on the top of a cylindrical tower, formed of a central solid cylinder of masonry of about 6.5 feet diameter, the steps about 4 feet wide, and the outer cylindrical wall of about 3 feet in thickness; the total height from the ground to the floor of the equatorial being about 70 feet.
Fig. 113 is a section across the Salle Centrale at (Fig. 112), showing the interior elevation of the end next this tower. From the centre of the lintel of the doorway at , a nearly vertical fissure, open 0.20 inch at bottom, extends upwards, becoming evanescent at about twelve feet, and its plane is in that of the meridian. Its continuation downwards can be traced from the centre of the sill of the doorway also.
A second fissure at B, occurs right through the outer wall, at right angles to the former, or east and west, and extends about ten feet up and down, (commencing where the wall had been weakened by an aperture now built up) and vertical—width 0.15. It is higher up the tower by five feet, than the fissure at its mid length. The inertia of the central core of masonry here is enormous in relation to its base; and to that, no doubt, is due these fissures, the only two formed in the whole building, which is solidly and well built of rubble and ashlar masonry.
The fissure appears to have been produced by the spiral lapping of the staircase round the central column (through which the push of the latter was transmitted to the cylindrical shell) having prevented its vibration as a simple pendulum in the plane of the shock, or near it, and induced a movement of conical vibration. The movement indicated is one nearly from south to north by compass.
Several other buildings in and directly around Naples were fissured, but none were thrown down. Amongst those which I examined were Messrs. Turners' bank, in St. Lucia, the Tribunale, and several palazzi, amongst the latter the Palazzo Lieti, in the Toledo. In no case, however, could I find that the fissures had been originated by the shock of 17th December: they were all pre-existent, and due chiefly to settlements, but had all been slightly enlarged by the shock.
The derangement at the Palazzo Lieti was so considerable as to demand prompt measures to prevent the fall of one wall of the interior court, by building up solidly, a huge arched porte-cochère that had yawned beneath it, and was about twenty-four feet span, with a new wall and smaller arch as in dotted lines Fig. 114.
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The building, consisting of four lofty storeys, and nearly eighty feet in height, I found had been fissured from settlements for a length of time; but the shock had been sufficient to shake downwards the central mass of the wall between and , and to widen all the old fissures, which were now three-quarters of an inch wide—those and widest at top, widest at bottom—evidencing clearly the nature of their production.
This, I found, was considered the most formidable example of injury to buildings occurring in or around Naples.
In no case, except at the Observatory, was I able to remark an original fissure in any well-built and sound structure.
The actual range of movement at Naples must have been small and far from violent. The amount of alarm produced generally by the shock was, however, sufficiently great to cause almost the whole population of the city to spend the remainder of the night of the 16th December in the open air, in carriages, around large fires in the streets, &c. The principal source of alarm described by most persons was from the creaking and straining noises of the timber work of the heavy floors and roofs, and the rattling of the windows and doors. A large portion of the population spent the succeeding night of the 17th December also in the open air, or in parading the public places. It was manifest, however, that much of this on both nights arose from the excitement and newsmongering tendencies of the people, who made a sort of "festa" of the occasion, and but little from actual terror except at the first moment.
From some persons of observation and discretion, I collected, their own perceptions of the phenomena.
A young English lady, residing in Santa Lucia, of much intelligence and observation, was at tea with some friends, sitting round a table whose length was nearly E. and W. by compass. Her attention was first arrested by a transverse movement of the table sliding back and forwards about an inch each way upon the waxed tiles of the floor. This she at first thought arose, from some of those who sat with her, but on casting her eyes upwards, on hearing the floor above creaking, she saw that a lamp suspended from the centre of the ceiling was oscillating also. Earthquake, which she had experienced elsewhere, then occurred to her, and she noticed carefully both the direction in which the lamp swung and the arc of its oscillation. She set the lamp itself again swinging for me, above the same table, in as precisely the same direction and to the same extent as possible. The direction I found to be 8° 0' E. of N. by compass, and the summit of Vesuvius bears 110° E. of N. from the front window of the room (which was on the second floor from the ground). The chord of the arc of vibration was 1012 inches, and the lamp makes thirty double oscillations per minute by the watch; it weighs about 12 lbs.
Her sensation of the shock, was of a small, rapid, recurrent, movement, forward and back, perfectly horizontal, without any undulating motion; then a cessation for two or three minutes (as estimated), and again a renewal of the same motions; after which all was quiet.The late Dr. Lardner was residing with his family at the Hôtel des Iles Britanniques, in Chiaja, and was at the time in a "salon" upon the third floor. His impressions were of a larger amount of oscillation, and with more or less of undulation. He has recorded them (with, perhaps, a little excess of colouring) in a letter published in the Times of 29th December, 1857, under date 19th December. He obligingly went with me to the "salon" at the hotel, wherein we found a large and ponderous chandelier hanging, of which he had observed the swing on the night of shock. He set it again in movement in the same direction and to the same extent.
This chandelier weighed 190 lbs. avoirdupois, hung (to the lowest point) 8 feet 9 inches from the ceiling, and by trial made 2012 double oscillations per minute.
According to Dr. Lardner, it commenced to swing in an arc of about 24 inches chord, and in one plane, the azimuth of which I found to bear 13° 0' E. of N., the Point of Pausillipo bearing 130° W. of N. from the front windows of the room. This vibration rapidly became elliptical, the major axis diminishing from 24 inches until it became about 12 inches; when the lamp continuing to vibrate as an ellipto-conic pendulum, was stopped by Dr. L., as he stated, both to appease the alarm of his family and to enable him to observe the effect of a renewed shock. The time by his watch was 10h 15' Naples mean time, but he could not guarantee that the watch was perfectly right, though a good one.
His sensation of the first movement was of a short, jarring, horizontal oscillation, that made all doors and windows rattle, and the floors and furniture creak. This ceased, and after an interval that seemed but a few seconds was renewed with greater violence, and, he thought, with a distinctly undulatory movement, "like that in the cabin of a small vessel in a very short chopping sea." It was sufficient to demand a certain amount of attention and effort, on the part of those standing up, to maintain their equilibrium.
Signor Guiscardi, a highly intelligent observer, educated as an architect and civil engineer, and well acquainted with physical science generally, had just retired to bed, when his attention was aroused by the first movement, which he describes by a little diagram, as simply a short sharp, jerking movement forward and back, thus:—
within narrow limits, and lasting, as he supposes, about five to seven seconds; then a total pause of some seconds, and then the former movement recommenced with rather more violence, and in this sort of order—
an interval of almost complete rest occurring between two fits; this concluded the earthquake. He did not perceive any undulatory 
movement, nor any movement up and down, 
and is certain, the movement (as not unfrequently asserted in Naples) did not commence with a movement up and down. The "pendules" in his rooms, having a general E. and W. plane of vibration, were stopped at 10h 10' Naples time, but he cannot guarantee their accuracy as to time.
I was not enabled to gain any additional facts of importance, from conversation with Signor Capocci, ex-professor of astronomy, or with Signor Palmieri, professor of physics. Both agreed that the direction of wave movement was from S. to N., with more or less of an eastern or western swerve from the magnetic meridian.
There was no material alteration, either in inclination or declination of the magnetometers noticed; but Professor Palmieri's views are, that every eruption of Vesuvius and Etna, and probably every earthquake, is accompanied by great electrical disturbance, which, he supposes, may affect the magnet. His seismometer at the Observatory upon Vesuvius was affected by the shock. The magnetic declination is very variable, both in short periods of time and for adjacent localities in and about Naples, and he thinks continually alters with the state of Vesuvius. I myself ascertained the declination in St. Lucia to be only 9° west in one spot; but blocks of lava used in building, pavement, &c., all more or less magnetic, make such observations very uncertain. The mean declination, however, for Naples, I obtained from the Observatory = 14° 30' west in February, 1858; and this agrees with the monthly printed determinations of the Royal Marine Observatory at Naples.
The whole of these five observers above mentioned agreed, that the shock at Naples was not attended with any noise whatever, either preceding, during, or succeeding the movement.
One gentleman only in Naples described to me sensations of sickness felt by him during the shock, which he first perceived while playing cards. In his case my impression was, that the affection was due to nervous excitement and alarm only. Conversation generally with persons of all classes in Naples, only tended to increase on my part the caution necessary in attempting to found any conclusion upon statements of physical facts, so exaggerated and often inconsistent, as those in common circulation, though unaccompanied by intentional deception.
Signor Fiodo, Vico Baglievo, Strada Toledo, chronometer-maker to the Neapolitan Marine (who executed the needful repair and new rating to one of my English chronometers), I found a man of great intelligence, discretion in observation, and accuracy of thought, and from him I derived some of the most useful facts obtained at Naples.
In his "atelier" he has a regulator clock, with a heavy gridiron pendulum vibrating seconds, and, as I found, oscillating in an azimuth 20° E. of N. by compass. Resting upon the bottom of the clock-case, which is of polished chestnut, he had long placed a small steel anvil or parallelopiped of the exact dimensions shown and figured in Fig. 115, five sides of which are smooth, but black as when forged, and the sixth polished. This stood on edge, the polished side being next the pendulum (and behind it as one faced the clock), and the plane of this side, parallel with that of the oscillation—the polished surface being by measurement exactly 0.276 inch horizontally from the adjacent side of the screw at the bottom of the pendulum bob. The chord of oscillation of the pendulum measured at the screw was = 1.87 inch, and less than the parallel dimension of the steel block. A small amount of transverse movement, therefore, would be sufficient at any time to stop the clock by bringing the screw of the pendulum into contact with the face of the steel block.
On the morning of the 17th December, 1857, Signor Fiodo found this clock stopped, and the screw of the pendulum in contact with the south end of the steel block, which had been shifted from its place by the momentum of the pendulum, as in Fig. 115.
I shall recur to the inferences derivable from this in Part III. It is sufficient here to remark that the direction of wave movement indicated is one approximately 6° E. of N. The clock was going (tempo meridiano) or solar time for Naples, and was on the evening of the 16th December true to time within an error of 0.5 second. It had been stopped at 10h 13' 26" P.M., which was therefore the time of the first shock at Naples, within less than half a second the error of the clock (slow), + the minute fraction of time due to the increased semi-arc of vibration.
There were several other clocks, some with pendulums, but making half and quarter seconds beat, in Signor Fiodo's establishment, oscillating in directions approximating to the meridian, and to the prime vertical, but none were stopped, and on examination I found them not circumstanced so as to have been so.
I verified with care all the dimensions and particulars of the regulator that was stopped, and have not the smallest doubt either of the good faith upon which the facts taken from Signor Fiodo rest, or of the exactness of the conditions as observed by him, and the dimensions, &c., as taken by myself.
On passing into the Naples end of the tunnel (or grotto) at Pausillipo, I remarked several fine, keenly-drawn lines of nearly vertical fissures, in the perpendicular banks of yellow tufa at the right-hand, or S.E. side of the entrance, which appeared recent. The light, however, was not sufficient to enable me to decide. I therefore returned early the following morning, and by clear sunlight made a minute examination of those cracks (the occurrence of which no one had remarked as far as I could learn). I satisfied myself that they were very recent, that they were not due to any settlement or alteration by gravity alone, of the banks, nor due to any artificial work, or excavation.
The keenness of their external lips or edges, the absence of dust, cobwebs, or insect or vegetable life, within or across them, and their narrow and uniform breadth of opening about 0.2 inch, their general parallelism, and, above all, their direction in azimuth, with relation to the form and direction of face, of the bank, and their verticality, convinced me that they had been produced by the shock of the 16th December, and were due to the inertia of the enormous bank of tufa through which the tunnel has been cut. I found their direction to be such, as indicated distinctly a wave-path and direction, of between N. 20° W. and N. 38° W. The last extreme appeared to me doubtful, and as only derived from one cleft. I am disposed to adopt the former azimuth only.
Upon the whole, the indications of wave-path at Naples are meagre, though not indistinct, nor discordant. They vary between the limits of N. 13° E. and N. 20° W., or, omitting Pausillipo wholly, vary between N. 6° E. and N. 13° E., and comparing all the indications, seem to give a resultant path of, N. 6° to 8° E. as the most trustworthy.
This appeared to point to a focus somewhere at sea, beneath the gulfs of Salerno, or Polycastre, a first impression that became not a little puzzling, when brought into contact with the facts, as they developed themselves in the interior provinces, and at first, for a day or two, almost caused me to despair of being able to trace out the true focus at all, the fresh evidence as collected appearing to be quite conflicting; and it was not until after I had found reiterated proofs of an inland focus, that could not connect itself directly with Naples, that the solution of the difficulty began to appear, in showing the shock at Naples city, to have been merely a reflected and refracted one.