EARTHQUAKES.
“Diseased Nature oftentimes breaks forth
In strange eruptions: and the teeming earth
Is with a kind of colic pinched and vexed
By the imprisoning of unruly wind
Within her womb; which for enlargement striving,
Shakes the old beldam earth, and topples down
Steeples and moss-grown towers.”
Such is the theory of earthquakes as laid down by “Wild Will
Shakespeare.” Whether it be an expression of the popular belief of the
day, or a personal opinion, is not easy to determine. If the latter, he
had, as we shall see by and by, many predecessors in the same belief.
His metaphor, though more elegantly expressed, cannot compare with the
Indian’s for terseness and force: “Ground heap sick--heap belly ache--no
good!”
We have already seen that the forces producing earthquakes and volcanic
action are conceded to be practically identical. The latter seldom
occurs without the former; but the former are frequent in districts far
removed from any known vent of subterranean heat. So the expression of
Shakespeare is not so far wrong as might be, so far as our present
knowledge goes.
In the Hindoo cosmogony successive ages of the world are separated by
periods of chaos; and no wilder image of unreined destruction has fancy
ever dreamed. The earth is to be eternal. There is one eternal,
invisible spirit, Brahm, from whom springs Brahma, who creates a race of
gods. These frame the earth into orderly condition, and rule it for four
hundred thousand years. At the end of that time, the land and sea and
sky meet in gigantic ruin; the gods are no more, save only Vishnu, the
preserver. The sea covers all things and eternal night is accompanied by
eternal tempest.
Eternal is not strictly correct, however. This reign of destruction
lasts four hundred thousand years, during which time Vishnu sleeps on
the coils of the great seven-headed serpent of eternity, which floats
upon the gloomy sea. The long night over, Vishnu wakes and remodels the
earth, and peace and light resume their sway. Seven such cycles pass;
all things are annihilated, and Brahm sets about a new creation which
goes the same round.
The eastern wise men, fond of allegory and parable, doubtless intended
by this to express the persistence and order in the universe, even in
periods of the most inexplicable disaster; and to picture for the
ignorant the absolute eternity of God.
The thing was too good to let drop; and others added to it by asserting
the earth was upborne by an elephant who stood on the back of a
tortoise. The tortoise rested on a fish; the fish on water; the water on
air; the air on light; the light on darkness; the darkness on the Lord
only knows what. When these animals were somewhat wearied, they changed
their position, and the earth trembled.
Greece had a somewhat better myth of the giant Atlas, who bore the world
on his shoulders; but the old fellow’s gait was not of the steadiest.
Rome, not much given to manufacturing her myths _de novo_, imported the
Grecian fable. We have to-day appropriated the old fellow’s title for a
geography supposed to contain the whole earth. The figure is lost on
most.
But the alleged drunkenness of Atlas did not consort precisely with the
popular ideas of the proper conduct of a steady old porter in a
responsible position; and the mythmakers dragged in a new scapegoat in
the person of the Titan Typhon, or Enceladus, supposed to be entombed in
Mt. Ætna, as we have elsewhere noticed.
Inhabitants of parts of Farther India and of some Malayan islands
believe that far down in the bowels of the earth an immense tiger, Pelu,
lies asleep. The sole object of his existence is to destroy the earth;
but he may not do this till the human race is extinct. Then he will rise
to his feet, the earth will burst into fragments and fly into the
distant realms of space. It must of necessity follow that our feline
friend’s existence is a somewhat monotonous one, and to avoid ennui in
his cramped quarters, he passes much time in sleep. Waking occasionally,
and wishing like the German Barbarossa, to know if his time is come, he
cautiously raises a few hairs on his back. The earth trembles, and the
natives, rushing from their tottering houses throw themselves upon the
ground, shouting loudly “Pelu! Pelu!” to assure his tigership that they
are certainly alive. Satisfied on this point, the worshipful beast
composes himself for another nap.
Thor, the war god of the Norsemen, wielded a mighty hammer, Miolnir. In
the “Saga of King Olaf” we find Thor shouting:
“The blows of my hammer,
Ring in the earthquake.”
Another myth attributes the earthquake to the restlessness of the
serpent Midgard, who encircles the universe, his tail in his mouth.
Also, the wolf Fenrir, who is to take part in the final contest that
produces Ragnarok, is supposed to have occasional differences of opinion
before the time with certain of the fire giants. The earth is then
liable to be shaken.
Natives of the Tonga group, in the South Pacific, believed that their
hero-god, Maui, upheld the world on his breast. When he became restless
and shook the earth, they would rush out and beat the ground with sticks
to make him lie still.
[Illustration: EFFECT OF A POWERFUL EARTHQUAKE ON MASSIVE MASONRY,
ITALY.]
From traditions concerning Mohammed we learn that the circular earth
lies in the midst of a vast sea, and is encircled by an immense whale,
upon whose back 700,000 gigantic bulls walk up and down. Said whale
swims about the earth very cautiously, but occasionally jostles it
slightly. On the night when Mohammed was born this noble animal was so
agitated with joy, that had not the Lord restrained him, he would
assuredly have overturned the earth.
The Sandwich Islanders believed that the goddess Pele, who dwelt in the
great volcano of Kilauea, was displeased with the conduct of man; she
proceeded to admonish him of her power, by shaking him out of bed in the
night, or tumbling his house about his ears. If especially angry, she
set her volcanic home to fuming and firing.
So-called scientific theories on various topics have in time past been
little more respectable, and need not be given any detailed attention.
The pious gentry who deemed Roger Bacon a wizard and Columbus and
Galileo heretics, would have listened with horror to any effort to
explain the phenomena of earthquakes as anything else than a direct
manifestation of the wrath of God. Researches in any branch of natural
science met with decided discouragement in Christendom during the dark
and middle ages; and the goddess of wisdom found a decidedly more
congenial atmosphere at Moorish and Saracen courts.
Hence the modern science of seismology, as the investigations of
earthquakes are called, is comparatively in its infancy. Yet the subject
of seismic phenomena has been of interest to the thoughtful from a very
early period, earthquakes being of far greater frequency than most
persons suppose. Some of the earliest philosophers ventured opinions on
the topic; for the records of earthquakes, more distinctly than those of
volcanoes, go back to the earliest times.
We find Aristotle, in his treatise on natural events, rejecting the
explanations of three other philosophers as untenable, and propounding a
theory of his own. Anaximenes, of Miletus, suggested the drying and
moistening of the earth occasioned irregular contraction and expansion,
and from the cracking and readjusting shocks resulted. Democritus, of
Abdera, shook his earth by means of vast subterranean bodies of water
which some force compelled to move from one cavity to another. Doubtless
the peculiar wave-like motion of the earth in many earthquakes suggested
his theory. Anaxagoras, of Clazomenae, believed that ether--by which the
old Greeks seem to mean air--was confined in underground cavities, and
in its efforts to escape upward produced the vibration of the earth.
Aristotle substitutes for the disturbing agent wind, which has flowed
into fissures and caverns and is endeavoring to flow out again. Virgil
and Pliny stand by the old Greek; and it is quite probable that
Shakespeare acquired his idea from one of the three. And these, with
Anaxagoras, are but little out of the way; for as seen in the discussion
of volcanic action, the explosive or disturbing agent is generally
steam, though other gases are present in large quantities.
We have already noticed that earthquakes and volcanoes are produced by
the same causes; but as the myths of many nations do not connect the
two, it is evident that such people did not recognize their essential
identity.
But after knowing they are but variations in results, we cannot so
readily explain the reason of the variations. Certain facts are well
established; and from these common premises widely different conclusions
have been deduced.
We know to-day that in active volcanic regions, an earthquake almost
invariably precedes an eruption; and a violent one has never, within the
historic period, followed an eruption. So the most reasonable inference
is, that the earthquake merely betokens the presence of a vast quantity
of imprisoned vapor which has not found an outlet; and that so soon as a
volcanic vent is found, the pressure is relieved, and the earthquake
subsides.
But this leaves us just where the theorists of volcanic agency have
stopped. The question of the sudden formation of volumes of gases in
sufficient quantities to produce such terrible effects is to be solved.
Mr. Mallet, who is one of the best authorities on the subject, considers
that submarine eruptions must account for them. A volcanic upheaval of
the sea bottom would produce crevices, by which the sea is brought
directly in contact with subterranean fires. An explosion is the result,
like those that have occasionally occurred at foundries from dumping
masses of fiery slag into a snowbank. So what began with a gradual
upheaval ends with a sudden concussion, the vibration of which passes
along the sea bottom to the mainland. Every one who has lived in the
city is familiar with the fact that the vibration produced by a carriage
may be felt at the top of a very tall building.
But the idea that the explosion always occurs at the sea bottom leaves
no way to account for the fact that a volcanic eruption acts as a
safety-valve. Mr. Mallet’s conclusions are largely based on personal
observations of earthquakes in England, where no active volcano exists.
That earthquakes are more violent and volcanoes more numerous on islands
or near the sea coast is well-known. It is also well established that
shocks frequently occur at sea, which are not perceptible on the land.
The shock is similar to that produced by striking on a reef. Often have
sailors been mystified, on receiving such shocks and hastily heaving the
lead, to find the ocean unfathomable. Again, shocks which are most
violent on land are not perceptible at sea, unless a great sea wave be
produced; but such a wave in the open sea, as often experienced,
produces no shock but passes under a vessel like a heavy swell. And a
shock at sea is sometimes severe enough to snap a spar, or wrench loose
bolts like the blow of a reef, yet no trace is perceptible on shore.
Lastly, earthquakes often happen in inland regions, and affect but a
small area. Clearly it will not do to attribute effects so different to
explosions at the sea-bottom.
Those who attribute all earthquakes to subterranean heat and gases,
whether local or general, find it easy to account for the occurrence of
violent earthquakes in regions remote from active volcanoes. In case of
the gradual decline of volcanic action, such as we know from the great
numbers of extinct volcanoes, old trap-dykes, and ancient lava beds, to
be continually taking place in one region or another, the old vents or
safety-valves would cool and close. The pent up power would in
consequence gradually accumulate, till finding no outlet, it would burst
the crust over a wide area, and so relieve the pressure.
This finds further confirmation in the fact that the noted non-volcanic
regions which are seriously shaken are all coincident with or adjacent
to regions of extinct fires; while in such regions as are very seldom
shaken, such as Germany, portions of North America, Brazil, the eastern
slope of the Andes, the traces of such agency are less common, or of
older date. Noted regions of volcanic action of comparatively recent
extinction are Asia Minor, Turkey, Spain, Southern France and Greece.
These, belted together by the active regions of Western Asia, the
peninsula of Arabia, the Mediterranean, and Azores and Canaries, form a
region which has suffered from earthquakes as much as, if not more than,
any other tract upon the globe.
Those who have been puzzled by the appearance of earthquakes some
distance from any actively volcanic region, have endeavored to divide
earthquakes into two classes, which they have called volcanic and
plutonic. This second class they have considered as originating, like
the other, in the depths of the earth; but have endeavored to account
for them by supposing them to be occasioned by the falling in of great
caverns at a considerable depth. This theory has found a fair objection
in the fact that in such cases an earthquake should always be a sinking
of the ground: while the wrecking power and peculiarities of some
earthquakes indicate a decided upward concussion as the first of shocks;
and at the seashore, where any change in level is at once detected,
upheaval is quite as common as subsidence.
Much speculation has been spent upon the fact of an earthquake being
very severe in two or three different localities, but being
imperceptible or very mild in intervening places. In South America it
has become so common a peculiarity that the natives speak of such
localities as “bridging” the earthquakes. Not improbably the reason is
the same that produces calm when two waves interfere, crest to trough;
the motions destroy each other. It may be also that the character of the
underlying rocks has much to do with such cases. Experiments with
explosions in mines show that vibrations of the soil travel over three
hundred yards per second through sand beds, or about as rapidly as in
the air; over five hundred yards in granite; while through iron they
travel over three thousand eight hundred and fifty yards per second. So
a vibration extremely destructive to a region underlaid by massive rocks
might be comparatively harmless to a town on a sand-bed or mud-bank.
Observations on earthquakes themselves have shown great variation in the
rate of speed. The earthquake of Germany of 1846 moved four hundred and
ninety-two yards per second; while the earthquake of Viege in 1855
traveled nine hundred and sixty yards a second toward Strasburg, but
only half that speed towards Turin. So, also, the Lisbon earthquake
traveled three times as rapidly around the coast as down the Rhine
valley. So it must be that certain regions owe their comparative
immunity from earthquakes to the nature of the ground beneath.
One or two ingenious savants have suggested that the earth is a vast
thermo-electric pile, and that disturbances in the electrical
equilibrium of the earth are the cause of earthquakes and volcanic
eruptions. But as already seen, the electrical phenomena of volcanic
eruptions are fairly considered an effect, and not a cause, of the
eruptions, as the hydro-electric machine illustrates. In the theory of
these men, the molten veins of the interior represent conductors which
are too small or imperfect to allow the electricity to pass freely, and
are fused in consequence. One of these men, Steffens, alleges that such
phenomena can only occur where large veins of coal exist, because large
masses of carbon would be necessary to keep up a strong electric tension
in the interior. Herr Steffens must account for the fact that the great
coal regions of the world have been peculiarly favored in their
comparative immunity from shocks.
Still others have advocated the idea that atmospheric whirlwinds and
cyclones produce earthquakes. While not a few shocks have been
accompanied by violent storms, the exception seems to be the rule. And
in the case of storms, we have seen that the outpour of heat and vapor
in a volcanic eruption would necessarily produce one. As concerns the
winds that have accompanied earthquakes, they have as often come after
the shock as before.
But these bring up certain phenomena that must be noticed. It is not
easy to say how great is the connection between electrical and
atmospheric disturbances, and the shiverings of the earth; but that
there is some peculiar bond between them has been thought indisputable.
It is only in the present century that scientists have carefully conned
this matter, and generally rejected the belief. But the opinion is very
ancient, and has a strong hold upon the people. It is generally adhered
to by South Americans, Italians, West Indians, Japanese, and the
inhabitants of Central Asia. Kamtschatkans, Kurile Islanders and
Japanese, assert shocks are most frequent at the equinoxes. In
equatorial America, the natives say an earthquake is preceded by
drought, and is the precursor of rain. In the Dauphiny Alps, the people
regard earthquakes as the result of avalanches; and the latter are
readily started by the slightest atmospheric disturbances. In Central
America the equinoctial idea prevails.
These things set the wise men to investigating. Much to their surprise,
they began to discover that the idea of connection between the seasons
and shocks seemed well-grounded. In 1834 Professor Merian announced that
of one hundred and eighteen earthquakes at Basle, the majority had
occurred in the winter. Volger made a list of twelve hundred and thirty
shocks in the Alps; seven hundred and seventy-four occurred in autumn
and winter. December showed one hundred and sixty-eight; July forty. Of
ninety-eight quite severe shocks, but one had occurred in the summer. Of
five hundred and thirty-nine earthquakes in the Rhine basin, one hundred
and three occurred in the spring, one hundred and one in the summer, one
hundred and sixty-five in the autumn, one hundred and seventy in winter.
Observations in the Antilles show a slight predominance of autumn and
winter.
Another peculiar fact is that most shocks seem to occur at night. Out of
four hundred and seventy-two earthquakes in 1855-56, whose time was
exactly noted, but one hundred and seventy-two happened in the day. Of
those at night, three-fifths were during the latter half, forty-four
being between one and two o’clock. Squier has told us that during
several years residence in Central America, nearly all shocks occurred
at night; also, that he experienced none save at the change of seasons.
Hence, one is almost compelled to conclude that, while the primal cause
of earthquakes must exist in the depths of the earth, yet external and
climatic influences are strong modifiers.
Some other peculiarities are adduced to show the connection between
atmospheric disturbances and earthquakes. In Central and Tropical
America the temperature is said to fall after any shock. After the
earthquake at Lechsand, Sweden, in 1856, the temperature fell eighty-six
degrees. The same shock was violent as far as Smyrna in Asia Minor,
where the thermometer fell at once twenty-nine degrees, the night being
the coldest of the winter. Many similar cases are mentioned. But in view
of the fact that one hundred times as many sudden and marked changes of
temperature occur every year in various localities without the
intervention of an earthquake, it seems difficult to regard the above
instances as more than mere coincidences. The greatest fall in
temperature the writer ever experienced occurred within three hours of a
transit of Venus; but one swallow--nor a flock of them--cannot make a
summer.
Barometric observations have been dragged into the combat. The great
Lisbon earthquake, and the convulsion in Calabria, were preceded by low
barometer. Similar observations have been made in this century. The
constantly recurring shocks of 1855-56 were in each case preceded by
fall of barometers. But Humboldt, in South America, and Ehrmann, in
Central America, were unable to find such order; though the shocks were
so invariably followed by such changes that unusual earthquakes were
believed by the natives (as is also believed in India) to advance the
rainy season. The resultant electric phenomena might produce this
expedition.
But in this field all at present is mere guess work. The exceptions to
any association of earthquake and storm are so far the rule; except in
case of a volcanic eruption also occurring. In the latter case a storm
invariably follows, so far as present observations go; but then the
storm is not co-extensive with the earthquake, but is usually confined
to the neighborhood of the volcano.
It should be noticed that certain scientists have endeavored to prove
these convulsions are due to planetary influence. It does not appear
that they have been able to find the least trace of any connection
between the earth’s convulsions and the planets; but some affirm the
existence of an earthquake cycle coincident with the Saros of the moon.
Effort is also made to connect earthquakes and volcanoes with the
gigantic convulsions of the sun, known as “sun spots.” It is argued by
certain advocates of the molten interior that the attraction of the sun
and moon produces an interior tidal wave, like that of the sea; and any
irregularities in this produce the phenomena of earthquakes and volcanic
eruptions. Objections to the molten interior have been already noted;
and in regard to the other suggestions, so long as the great convulsions
are peculiarly prevalent in certain regions, so long it will be
necessary to seek their chief cause or most powerful modifiers in
entirely local influences.
In conclusion, it does not yet seem clear that we can rely absolutely
upon a single cause as productive of all the convulsions of the earth’s
crust. Internal local heat, pent up gases, suffice for volcanic
phenomena; but earthquakes present so many peculiar variations that it
seems almost imperative to many men to admit, at least, the modifying
influence of other agencies. But so long as these agencies appear to be
quite as frequently the modified as the modifier, no laws concerning
them can be announced. Hence, internal conditions are the only clearly
identified factors so far.
There is quite as much difference of opinion as to how far beneath the
surface the shocks originate. Robert Mallet’s investigations have led
him to believe the depth cannot be over thirty miles, and that seven or
eight miles is the limit for most, and his views are those of most
scientists. But a few others conclude that we cannot find molten matter
and gases to produce the concussion at a less depth than seventy-eight
miles. But, as their conclusions are based largely upon the idea that
the melting point of minerals is raised uniformly with increasing
pressure, their conclusions must be rejected as unreliable.
The character of the motion is well known. Each point of the surface
begins to move with the vibration first upwards, then away from the
center of shock, then downward and backwards. Thus, each point describes
a small ellipse, which is repeated with each wave of vibration. If the
longer axis of the ellipse be vertical, the main force of the concussion
is directed upwards; if the shorter one be upright, the shock is an
undulatory one. An alternation of the two forms the most destructive
combination. The difference is readily perceived in the effects
produced. A sudden upward shock may wreck the roofs or floors of
buildings, while an undulatory one brings down the walls.
Houses erected on sand, immediately overlaying compact rock, usually
suffer most during earthquakes. The effect is that of the vibration of a
sheet of glass covered with sand. But, if a second sheet of glass be
placed on that, the vibration is hardly communicated to it at all. So,
while sand is a bad foundation, a sand-bed beneath the surface seems to
deaden the shock.
It is not difficult to understand that lofty buildings, and those of
stone or brick, must be vastly more dangerous than those of wood, and
low and broad. Throughout many portions of Central and South America,
the people endeavor to compromise, by building houses of stone, but low
and massive, with very light roofs. These are far less safe than light
structures of wood; also, it is clear that cupolas and towers must be
peculiarly liable to injury. For this reason, churches have often
suffered more from shocks than other buildings, and the throngs of
penitents who flock to them in the hope of propitiating an offended
providence are often the first victims of an earthquake.
“It is to earthquakes, rather than to barbarians, from the fifth to the
ninth century, that Rome owed the loss of so many superb palaces and
temples. One might imagine that in these great disasters, the architect
is the ally of the subterranean scourge. The Indian’s hut and the Arab’s
tent, may be overturned without any great loss or injury to their
owners; but the marble of the patrician crushes him as it falls, and the
inhabitants of a great city meet their death under the ruins of their
sumptuous buildings. The Peruvians of old were not far wrong in making
merry at the folly of their Spanish conquerors, who, in erecting great
buildings upon a soil so constantly agitated, were preparing, at great
expense, their own tombs.”
It will be shown, by and by, how the motions of earthquakes are becoming
so carefully noted that their path can be pointed out beforehand. Ere
many years are past, the prediction of earthquakes may become as
important a feature of the Signal Service Department, as the foretelling
of storms.