The Different Resistance Offered By The Walls, According To
Their Direction, Was Well Exemplified In The Case Of The
Cathedral.
The side which fronted the N.E. presented a grand
pile of ruins, in the midst of which door-cases and masses
of timber stood up, as if floating in a stream.
Some of the
angular blocks of brickwork were of great dimensions; and
they were rolled to a distance on the level plaza, like
fragments of rock at the base of some high mountain. The side
walls (running S.W. and N.E.), though exceedingly fractured,
yet remained standing; but the vast buttresses (at
right angles to them, and therefore parallel to the walls that
fell) were in many cases cut clean off, as if by a chisel, and
hurled to the ground. Some square ornaments on the coping
of these same walls, were moved by the earthquake into
a diagonal position. A similar circumstance was observed
after an earthquake at Valparaiso, Calabria, and other places,
including some of the ancient Greek temples. [1] This twisting
displacement, at first appears to indicate a vorticose
movement beneath each point thus affected; but this is highly
improbable. May it not be caused by a tendency in each stone
to arrange itself in some particular position, with respect
to the lines of vibration, - in a manner somewhat similar to
pins on a sheet of paper when shaken? Generally speaking,
arched doorways or windows stood much better than any
other part of the buildings. Nevertheless, a poor lame old
man, who had been in the habit, during trifling shocks, of
crawling to a certain doorway, was this time crushed to
pieces.
I have not attempted to give any detailed description of
the appearance of Concepcion, for I feel that it is quite
impossible to convey the mingled feelings which I experienced.
Several of the officers visited it before me, but their
strongest language failed to give a just idea of the scene of
desolation. It is a bitter and humiliating thing to see works,
which have cost man so much time and labour, overthrown in one
minute; yet compassion for the inhabitants was almost instantly
banished, by the surprise in seeing a state of things produced
in a moment of time, which one was accustomed to attribute
to a succession of ages. In my opinion, we have scarcely beheld,
since leaving England, any sight so deeply interesting.
In almost every severe earthquake, the neighbouring waters
of the sea are said to have been greatly agitated. The
disturbance seems generally, as in the case of Concepcion, to
have been of two kinds: first, at the instant of the shock,
the water swells high up on the beach with a gentle motion,
and then as quietly retreats; secondly, some time afterwards,
the whole body of the sea retires from the coast, and then
returns in waves of overwhelming force. The first movement
seems to be an immediate consequence of the earthquake
affecting differently a fluid and a solid, so that their
respective levels are slightly deranged: but the second case
is a far more important phenomenon. During most earthquakes,
and especially during those on the west coast of
America, it is certain that the first great movement of the
waters has been a retirement. Some authors have attempted
to explain this, by supposing that the water retains its level,
whilst the land oscillates upwards; but surely the water close
to the land, even on a rather steep coast, would partake of the
motion of the bottom: moreover, as urged by Mr. Lyell,
similar movements of the sea have occurred at islands far
distant from the chief line of disturbance, as was the case
with Juan Fernandez during this earthquake, and with
Madeira during the famous Lisbon shock. I suspect (but the
subject is a very obscure one) that a wave, however produced,
first draws the water from the shore, on which it is advancing
to break: I have observed that this happens with the little
waves from the paddles of a steam-boat. It is remarkable
that whilst Talcahuano and Callao (near Lima), both situated
at the head of large shallow bays, have suffered during
every severe earthquake from great waves, Valparaiso,
seated close to the edge of profoundly deep water, has never
been overwhelmed, though so often shaken by the severest
shocks. From the great wave not immediately following the
earthquake, but sometimes after the interval of even half an
hour, and from distant islands being affected similarly with
the coasts near the focus of the disturbance, it appears that
the wave first rises in the offing; and as this is of general
occurrence, the cause must be general: I suspect we must
look to the line, where the less disturbed waters of the deep
ocean join the water nearer the coast, which has partaken
of the movements of the land, as the place where the great
wave is first generated; it would also appear that the wave
is larger or smaller, according to the extent of shoal water
which has been agitated together with the bottom on which it
rested.
The most remarkable effect of this earthquake was the permanent
elevation of the land, it would probably be far more
correct to speak of it as the cause. There can be no doubt
that the land round the Bay of Concepcion was upraised
two or three feet; but it deserves notice, that owing to the
wave having obliterated the old lines of tidal action on the
sloping sandy shores, I could discover no evidence of this
fact, except in the united testimony of the inhabitants, that
one little rocky shoal, now exposed, was formerly covered
with water. At the island of S. Maria (about thirty miles
distant) the elevation was greater; on one part, Captain Fitz
Roy founds beds of putrid mussel-shells _still adhering to the
rocks_, ten feet above high-water mark: the inhabitants had
formerly dived at lower-water spring-tides for these shells.
The elevation of this province is particularly interesting,
from its having been the theatre of several other violent
earthquakes, and from the vast numbers of sea-shells scattered
over the land, up to a height of certainly 600, and I
believe, of 1000 feet.
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