CHAPTER IX._Earthquakes and other earth movements

DISTURBANCES IN THE OCEAN.

Sea vibrations—Cause of vibratory blows—Sea waves: Preceding

earthquakes; Succeeding earthquakes—Magnitude of waves—Waves

as recorded in countries distant from the origin—Records on

tide gauges—Waves without earthquakes—Cause of waves—Phenomena

difficult of explanation—Velocity of propagation—Depth of the

ocean—Examples of calculations—Comparison of velocities of

earthquake waves with velocities which ought to exist from the

known depth of the ocean.

_Sea vibrations._—Whilst residing in Japan I have had many

opportunities of conversing with persons who had experienced

earthquakes when on board ships, and it has often happened that these

same earthquakes have been recorded on the shore. For example, at the

time of every moderately severe earthquake which has shaken Yokohama,

the same disturbance has been felt on board the ships lying in the

adjoining harbour. In some cases the effect had been as if the ship

was grounding; in others, as if a number of sharp jerks were being

given to the cable. The effect produced upon a man-of-war lying in the

Yokohama harbour on the evening of March 11, 1881, was described to me

as a ‘violent irresistible shaking.’ Vessels eighty miles at sea have

recorded and timed shocks which were felt like sudden blows. These were

accompanied by a noise described as a ‘dull rattle like thunder.’

In none of the cases here quoted was any disturbance of the water

observed.

The great earthquake of Lisbon was felt by vessels on the Atlantic,

fifty miles away from shore.

On February 10, 1716, the vessels in the harbour of New Pisco were so

violently shaken that both ropes and masts were broken, and yet no

motion in the water was observed. Some have described these shocks like

those which would be produced by the sudden dropping of large masses of

ballast in the hold of the vessel. Other cases are known where rigging

was damaged, and even cannon have been jerked up and down from the

decks on which they rested.

_Cause of vibratory blows._—From the rattling sound which has

accompanied some of these submarine shocks, many of which, it may be

remarked, have never been recorded as earthquakes upon neighbouring

shores, it does not seem improbable that they may have been the result

of the sudden condensation of volumes of steam produced by submarine

volcanic eruptions.

As confirmatory of this supposition we have the fact, that many of

the marine disturbances which might be called ‘sea-quakes,’ have been

observed in places which are close to, or in the line of, volcanic

vents. Thus, M. Daussy, who has paid special attention to this subject,

has collected evidence to show that a large number of shocks have been

felt by vessels in that portion of the Atlantic between Cape Palamas,

on the west coast of Africa, and Cape St. Roque, on the east coast of

South America.[73]

Some of the vessels only felt shocks and tremblings, but others saw

smoke, and some even collected floating ashes. In considering the

submarine shocks of this particular area, we must bear in mind that it

lies in the line of Iceland, the west coast of Scotland, the Azores,

Canaries, Cape de Verd Islands, St. Helena, and other places, all of

which, if not at present in volcanic activity, shew evidence of having

been so within recent times. The connection between volcanic action and

earthquakes will be again referred to.

_Sea waves._—Although in the above-mentioned instances sea waves have

not been noticed, it is by no means uncommon to find that destructive

earthquakes have been accompanied by waves of an enormous size, which,

if the earthquake has originated beneath the sea, have, subsequently

to the shaking, rolled in upon the land, to create more devastation

than the actual earthquake. It may, however, be mentioned that a few

exceptional cases exist when it is said that the sea wave has preceded

the earthquake, as, for example, at Smyrna, on September 8, 1852.

Again, at the earthquake in St. Thomas, in 1868, it is said that the

water receded shortly _before_ the first shock. When it returned, after

the second shock, it was sufficient to throw the U.S. ship ‘Monagahela’

high and dry.[74]

Another American ship, the ‘Wateree,’ was also lost in 1868 by being

swept a quarter of a mile inland by the sea wave which inundated

Arequippa.

Much of the great destruction which occurred at the time of the great

Lisbon earthquake was due to a series of great sea waves, thirty to

sixty feet higher than the highest tide, which swamped the town. These

came in about an hour after the town had been shattered by the motion

of the ground.

The first motion in the waters was their withdrawal, which was

sufficient to completely uncover the bar at the mouth of the Tagus.

At Cadiz, the first wave, which was the greatest, is said to have been

sixty feet in height. Fortunately the devastating effect which this

would have produced was partially warded off by cliffs.

At the time of the Jamaica earthquake (1692) the sea drew back for a

distance of a mile.

In South America sea waves are common accompaniments of large

earthquakes, and they are regarded with more fear than the actual

earthquakes.

On October 28, 1724, Lima was destroyed, and on the evening of that day

the sea rose in a wave eighty feet over Callao. Out of twenty-three

ships in the harbour, nineteen were sunk, and four others were carried

far inland. The first movement which is usually observed is a drawing

back of the waters, and this is so well known to precede the inrush of

large waves, that many of the inhabitants in South America have used it

as a timely warning to escape towards the hills, and save themselves

from the terrible reaction which, on more than one occasion, has so

quickly followed.

At Caldera, near to Copiapo, on May 9, 1877, which was the time when

Iquique was devastated, the first motion which was observed in the sea

was that it silently drew back for over 200 feet, after which it rose

as a wave over five feet high. At some places the water came in as

waves from twenty to eighty feet in height.

At Talcahuano, on the coast of Chili, in 1835, there was a repetition

of the phenomena which accompanied the destruction of Penco in 1730

and 1751. About forty minutes after the first shock, the sea suddenly

retired. Soon afterwards, however, it returned in a wave twenty feet

high, the reflex of which swept everything towards the sea. These

phenomena were repeated three times.[75]

When Callao and Lima were destroyed, in 1746, the sea first drew back,

then came in as waves, four or five minutes after the earthquake.

Altogether, between October 28 and February 24, 451 shocks were

counted. At one time the sea came in eighty feet above its usual

level. One account says that the large waves came in forty-one and a

half hours after the first shock, and seventeen and a half hours after

comparative tranquillity had prevailed.[76]

At the eruption of Monte Nuovo, near Naples, in September 27, 1538, the

water drew back forty feet, so that the whole gulf of Baja became dry.

In 1696, at the time of the Catanian earthquake, the sea is said to

have gone back 2,000 fathoms. Instances are recorded where the sea has

receded several miles.

The time taken for the flowing back of the sea is usually very

different. Sometimes it has only been five or six minutes, whilst at

other times over half an hour, and there are records where the time is

said to have been still longer.

Thus, at the earthquake of Santa (June 17, 1678), the sea is stated to

have gone as far back as the eye could reach, and did not rise again

for twenty-four hours, when it flooded everything.

In 1690 at Pisco the sea went back two miles, and did not return for

three hours. When it returns it does so with violence, and examples of

the heights to which it may reach have been given. The greatest sea

wave yet recorded, according to Fuchs, is one which, on October 6,

1737, broke on the coast of Lupatka, 210 feet in height.

There are, however, cases known where the sea has returned as gradually

as it went out. Thus, on December 4, 1854, when Acapulco was

destroyed, the sea is said to have returned as gently as it went out.

When sea waves have travelled long distances from their origin, as,

for instance, whenever a South American wave crosses the Pacific to

Japan, the phenomena which are observed are like those which were

observed at Acapulco; the sea falls and rises, at intervals of from ten

minutes to half an hour, to heights of from six to ten feet, without

the slightest appearance of a wave. Its phenomenon is like that of an

unusually high tide, which repeats itself several times per hour. Even

if we watch distant rocks with a telescope, although the surface of the

ocean may be as smooth as the surface of a mirror, there is not the

slightest visible evidence of what is popularly called a wave. The sea

being once set in motion it continues to move as waves of oscillation

for a considerable time. In 1877, as observed in Japan, the motion

continued for nearly a whole day. The period and amplitude of the rise

and fall were variable, usually it quickly reached a maximum, and then

died out gradually. As observed in a self-recording tide gauge at San

Francisco, the disturbance lasted for about four days. A diagram of

this is here given. In its general appearance it is very similar to the

records of other earthquake waves. The large waves represent the usual

six hours rise and fall of the tides; usually these are fairly smooth

curves. Superimposed on the large waves are the smaller zigzag curves

of the earthquake disturbance, lasting with greater or less intensity

for several days. As these curves are drawn to scale—horizontally for

hours, and vertically one fifth inch to the foot, to show the extent of

the rise and fall—they will be easily understood.

Sometimes, as in the present example, the first movement in the

waters is that of an incoming wave. In many instances, however, this

observation may be due to the slow and more gentle phenomena of the

previous drawing out of the water, which in a steep waste, or when the

water is rough, would be difficult to observe, not having been remarked.

The distance to which these sea waves have extended has usually been

exceedingly great.

[Illustration: FIG. 28.—Record of Tide Gauge at Port Point, San

Francisco. Showing Earthquake Waves of May 1877.]

The sea wave of the Iquique earthquake of May 9, 1877, like many of its

predecessors, was felt across the basin of the whole Pacific, from New

Zealand in the south, to Japan and Kamschatka in the north. And but for

the intervention of the Eurasian and American continents would have

made itself appreciable over the surface of the whole of our globe. At

places on the South American coast, it has been stated that the height

of the waves varied from twenty to eighty feet. At the Samoa Islands

the heights varied from six to twelve feet. In New Zealand the sea rose

and fell from three to twenty feet. In Australia the heights to which

the water oscillated were similar to those observed in New Zealand. In

Japan it rose and fell from five to ten feet. In this latter country,

the phenomena of sea waves which follow a destructive earthquake on the

South American coast are so well known that old residents have written

to the local papers announcing the probability of such occurrences

having taken place some twenty-five hours previously in South America.

In this way news of great calamities has been anticipated, details of

which only arrived some weeks subsequently. Just as the destructive

earthquakes of South America have announced themselves in Japan, in

a like manner the destructive earthquakes of Japan have announced

themselves upon the tide gauges of California. Similarly, but not so

frequently, disturbances shake the other oceans of the world.

For example, the great earthquake of Lisbon propagated waves to the

coasts of America, taking on their journey nine and a half hours.

_Sea waves without earthquakes._—Sometimes we get great sea waves

like abnormal tides occurring without any account of contemporaneous

earthquakes. Although earthquakes have not been recorded, these ill

understood phenomena are usually attributed to such movements.

Several examples of these are given by Mallet. Thus, at 10 A.M. on

March 2, 1856, the sea rose and fell for a considerable distance

at many places on the coast of Yorkshire. At Whitby, the tide was

described ebbing and flowing six times per hour, and this to such a

distance that a vessel entering the harbour was alternately afloat and

aground.

In 1761, on July 17, a similar phenomena was observed at the same place.

A like occurrence took place at Kilmore, in the county of Wexford, on

September 16, 1864, when the water ebbed and flowed seven times in the

course of two hours and a half. These tides, which appear to have taken

about five minutes to rise and five minutes to fall, were seen by an

observer approaching from the west as six distinct ridges of water. The

general character of the phenomena appears to have been very similar to

that which was produced at the same place by the Lisbon earthquake of

1755; and the opinion of those who saw and wrote about their occurrence

was that it was due to an earthquake disturbance. Such phenomena are

not uncommon on the Wexford coast, where they are popularly known as

‘death waves,’ probably in consequence of the lives which have been

lost by these sudden inundations.

They have also been observed in other parts of Ireland, the north-east

coast of England, and in many parts of the globe. They will be again

referred to under the head of earth pulsations.

_Cause of sea waves._—Mallet, who in his report to the British

Association in 1858, writes upon this last-mentioned occurrence at

considerable length, whilst admitting that many may have originated

from earthquakes, he thinks it scarcely probable that an earthquake

blow, sufficiently powerful to have produced waves like those observed

at Kilmore, should not have been felt generally throughout the south of

Ireland. He, therefore, suggests that sometimes waves like the above

might be produced by an underwater slippage of the material forming

the face of a submarine bank, the slope of which by degradation and

deposition, produced by currents, had reached an angle beyond the

limits of repose of the material of which it was formed. Mallet does

not insist upon the existence of these submarine landslips, but only

suggests their existence as a means of explaining certain abnormal sea

waves which do not appear to have been accompanied by earthquakes.

In the generality of cases sea waves are accompanied by earthquakes,

but it may often happen that the connection between the two is

difficult to clearly establish. One simple explanation for the origin

of waves occurring with earthquakes, is, that in consequence of the

earthquake a large volume of water suddenly finds its way into cavities

which have been opened, the disturbance produced by the inrush giving

rise to waves.

A second explanation is, that the land along a shore is caused by an

earthquake to oscillate upwards, the water running off to regain its

level. A supposition like this is negatived by the fact that these

disturbances are felt far away from the chief disturbance, on small

islands. Also, it may be added, that the whole disturbance appears to

approach the land from the sea, and not in the opposite direction.

Thus, in the earthquake of Oahu (February 18, 1871), it was remarked

that the shock was first felt by the ships farthest from the land.[77]

Another suggestion is that the waves are due to a sudden heaving up

of the bottom of the ocean. If this lifting took place slowly, then

the first result would be that the water situated over the centres of

disturbance would flow away radially in all directions from above the

area of disturbance.

If, however, the submarine upheaval took place with great rapidity, say

by the sudden evolution of a large volume of steam developed by the

entry of water into a volcanic vent, as the water was heaped above the

disturbed area, water might run in radially towards this spot.

Supposing a primary wave to be formed in the ocean by any such causes,

then the falling of this will cause a second wave to be formed,

existing as a ring round the first one. The combined action of the

first and second wave will form a third one, and so the disturbance,

starting from a point, will radiate in broadening circles. During the

up and down motion of these waves, the energy which is imparted to any

particle of water will, on account of the work which it has to do in

displacing its neighbours, by frictional resistance, gradually grow

less and less, until it finally dies away. The waves which are the

result of this motion will also grow less and less.

If a series of sea waves were produced by a single disturbance, we see

that these will be of unequal magnitude. Now, for small waves, the

velocity with which they travel depends upon the square root of their

lengths; but with large waves, like earthquake waves, the velocity

depends upon the square root of the depth of water, and these latter

travel more quickly than the former.

If, therefore, we have a series of disturbances of unequal magnitude

producing sea waves, which, from the series of shocks which have

been felt upon shores subsequently invaded by waves, seems in all

probability often to have been the case, it is not unlikely that the

waves of an early disturbance may be overtaken and interfered with by a

series which followed.

These considerations help us to understand the appearance of the

records on our tide gauges, and also the phenomena observed by those

who have recorded tidal waves as they swept inwards upon the land. For

instance, we understand the reason why sea waves, as observed at places

at different distances from the origin of a disturbance, should be of

different heights. We also see an explanation for the fact that small

waves should sometimes appear to be interpolated between large ones,

and that these should occur at varying intervals.

The fact that whenever a wave is produced, a certain quantity of water

must be drawn from the level which surrounds it, in order that it

should be formed, explains the phenomena that the sea is often observed

first to draw back. Out in the open ocean it is drawn from the hollow

between two waves. As has been pointed out by Darwin, it is like the

drawing of the water from the shore of a river by a passing steamer.

The difference in the height of waves, as observed at places lying

close to each other, is probably due to the configuration of the coast,

the interference of outlying islands, reefs, &c.—causes which would

produce similar effects in the height of tide.

As a wave approaches shallow water it gradually increases in height,

its front slope becomes steep, and its rear slope gentle, until finally

it topples over and breaks. This increasing in height of waves is

no doubt connected with the destruction of Talcahuano and Callao,

which are situated at the head of shallow bays. Valparaiso, which is

on the edge of deep water, has never been overwhelmed.[78] Another

case tending to produce anomalies in the character of waves would be

their reflection and mutual interference, the reflections due to the

configuration of the ocean bed and coast lines.

The complete phenomena which may accompany a violent submarine

disturbance are as follows:—

By the initial impulse of explosion or lifting of the ground, a ‘great

sea wave’ is generated, which travels shorewards with a velocity

dependent upon its size and the depth of the ocean. At the same

instant, a ‘sound wave’ may be produced in the air, which travels at a

quicker rate than the ‘great sea wave.’ A third wave which is produced,

is an ‘earth wave,’ which will reach the shore with a velocity

dependent on the intensity of the impulse and the elasticity of the

rocks through which it is propagated. This latter, which travels the

fastest, may carry on its back a small ‘forced sea wave.’ On reaching

the shore and passing inland, this ‘earth wave’ will cause a slight

recession of the water as the ‘forced sea wave’ slips from its back.

As these ‘forced sea waves’ travel they will give blows to ships

beneath which they may pass, being transmitted from the bottom of the

ocean to the bottom of the ships like sound waves in water. At the

time of small earthquakes, produced, for example, by the explosion of

small quantities of water entering volcanic fissures, or by the sudden

condensation of steam from such a fissure entering the ocean, aqueous

sound waves are produced, which cause the rattling and vibrating jars

so often noticed on board ships.

_Phenomena difficult of explanation._—Although we can in this way

explain the origin and phenomena of sea waves, we must remember, as

Kluge has pointed out, that it is not the simple backward and forward

movement of the ground which produces sea waves, and that the majority

of earthquakes which have occurred in volcanic coasts have been

unaccompanied by such phenomena. Out of 15,000 earthquakes observed on

coast lines, only 124 were accompanied by sea waves.[79] Out of 1,098

earthquakes catalogued by Perrey for the west coast of South America,

only nineteen are said to have been accompanied by movements in the

waters. According to the ‘Geographical Magazine’ (August 1877, p. 207),

it would seem that out of seventy-one severe earthquakes which have

occurred since the year 1500 upon the South American coast many have

been accompanied by sea waves. Darwin also remarks, when speaking of

South America, that almost every large earthquake has been accompanied

by considerable agitation in the neighbouring sea.[80]

On April 2, 1851, when many towns in Chili were destroyed, the sea was

not disturbed. At the time of the great earthquake of New Zealand (June

23, 1855), although all the shocks came from the sea, yet there was no

flood. The small shock of February 14, however, was accompanied by a

motion in the sea.

To these examples, which have been chiefly drawn from the writings of

Fuchs, must be added the fact that the greater number of disturbances

which are felt in the north-eastern part of Japan, although they

emanate from beneath the sea, do not produce any visible sea waves.

They are, however, sufficient to cause a vibratory motion on board

ships situated near their origin.

Another point referred to by Fuchs, as difficult of explanation,

is, that the water, when it draws back, often does so with extreme

slowness, and farther, in some instances, it has not returned to its

original level. That the sea might be drawn back for a period of

fifteen or thirty minutes is intelligible, when we consider the great

length of the waves which are formed. Cases where it has retired for

several hours or days, and when its original level is altered, appear

only to be explicable on the assumption of more or less permanent

changes in the levels of the ground. For example, in the earthquake

of 1855 which shook New Zealand, the whole southern portion of the

northern island was raised several feet.

These sudden alterations in the levels of coast lines have already

been referred to.

Other points which are difficult to understand are the occurrence

of disturbances in the sea at the time of feeble earthquakes, and

with earthquakes occurring in distant places. As examples of such

occurrences, Fuchs quotes the following: ‘On May 16, 1850, at 4.28

A.M., an earthquake took place in Pesth, and at 7.30 a motion was

observed in the sea at Livorno. Again, at the time of the earthquake

of December 19, 1850, which shook Heliopolis, a flood suddenly came

in upon Cherbourg.’ May not these phenomena be the result of an earth

pulsation, which produced an earthquake at one point, and a sea wave at

another?

Equally difficult to understand are the observations when the

disturbance in the sea has occurred several hours after an earthquake;

as, for instance, at Batavia, in 1852, when there was an interval of

two hours; and to this must be added the observations where the motion

of the sea has preceded that of the earthquake—as, for instance, in

1852, at Smyrna. Whilst recognising the fact that it is possible to

suggest explanations for many of these anomalies, we must also bear

in mind that they are, generally speaking, exceptional, and, in some

instances, may possibly be due to errors in observations.

_Velocity of propagation of sea waves, and depth of the ocean._—It

has long been known to physical science that the velocity with which

a given wave is propagated along a trough of uniform depth, holds a

relation to the depth of the trough.

If _v_ is the velocity of the wave, and _h_ the depth of the trough,

this relation may be expressed as follows:—

_v_^2 (_v_)

_h_ = ————— or _h_ = (———)^2

_g_ (_k_)

Where _g_ = 32·19 and _k_ = 5·671.

It will be observed that these two formulæ (the first of which is

known as Russell’s formula, and the second as Airy’s) are practically

identical.

The apparent difference is in the average value assigned to the

constant.

For large waves such as we have to deal with, it would be necessary,

if we were desirous of great accuracy, to increase the value of _h_

by some small fraction of itself. We might also make allowance for

the different values of _g_, according to our position on the earth’s

surface. With these formulæ at our disposal it is an easy matter, after

having determined the velocity with which a wave was propagated, to

determine the average depth of the area over which it was transmitted.

In making certain earthquake investigations the reverse problem is

sometimes useful—namely, determining the velocity with which a sea wave

has advanced upon a shown line, from a knowledge of the depth of the

water in which it has been propagated.

Calculations of the average depths of the Pacific, dependent on the

velocity with which earthquake waves have been propagated, have been

made by many investigators.

In most cases, however, in consequence of having assumed the wave to

have originated on a coast line, when the evidence clearly showed it

to have originated some distance out at sea, the calculations which

have been made are open to criticism. The average depths which I

obtained for various lines across the Pacific appear to be somewhat

less than the average depth as given by actual soundings. We must,

however, remember that the common error in actual soundings is that

they are usually too great, it being difficult in deep-sea sounding

to determine when the lead actually reaches the bottom. Until oceans

have been more thoroughly surveyed with the improved forms of sounding

apparatus, we shall not be able to verify the truth of the results

which have been given to us by earthquake waves.

EXAMPLES OF CALCULATIONS ON SEA WAVES.

1. _The wave of 1854._—This wave originated near Japan, and it was

recorded on tide gauges at San Francisco, San Diego, and Astoria.

On December 23, at 9.15. A.M., a strong shock was felt at Simoda in

Japan, which, at 10 o’clock, was followed by a large wave thirty feet

in height. The rising and falling of the water continued until noon.

Half an hour after, the movement became more violent than before. At

2.15 P.M. this agitation decreased, and at 3 P.M. it was comparatively

slow. Altogether there were five large waves.

On December 23 and 25, unusual waves were recorded upon the

self-registering tide gauges at San Francisco, San Diego, and Astoria.

At San Francisco three sets of waves were observed. The average time of

oscillation of one of the first set was thirty-five minutes, whilst one

of the second and third sets was almost thirty-one minutes.

At San Diego three series of waves were also shown, but with average

times of oscillation of from four to two minutes shorter than the waves

at San Francisco.

The San Francisco waves appear to indicate a recurrence of the same

phenomena.

The record at San Diego shows what was probably the effect of a

series of impulses, the heights increasing to the third wave, then

diminishing, then once more renewed, after which it died away.

The result of calculations based on these data were:—

+---------------+------------+------------+--------+--------------+

+---- ----------+------------+------------+--------+--------------+

| | | h. m. | | |

| Simoda to San | 4917 | 12 13 | 545 | 2100 |

| Simoda to San | 4527 | 12 39 | 528 | 2500 or 2230 |

+---------------+------------+------------+--------+--------------+

The difference for the depths in the San Francisco path depends whether

the length of the waves is reckoned at 210 or 217 miles. The length of

the waves on the San Diego path were 186 or 192 miles.[81]

_The wave of 1868._—On August 11, 1868, a sea wave ruined many cities

on the South American coast, and 25,000 lives were lost. This wave,

like all the others, travelled the length and breadth of the Pacific.

In Japan, at Hakodate, it was observed by Captain T. Blakiston, R.A.,

who very kindly gave me the following account:

On August 15, at 10.30 A.M., a series of bores or tidal waves

commenced, and lasted until 3 P.M. In ten minutes there was a

difference in the sea level of ten feet, the water rising above high

water and falling below low water mark with great rapidity. The

ordinary tide is only two and a half to three feet. The disturbance

producing these waves originated between Iquique and Arica, in about

lat. 18.28 S. at about 5 P.M. on August 13. In Greenwich time this

would be about 13h. 9m. 40s. August 13. The arrival of the wave at

Hakodate in Greenwich time would be about 14h. 7m. 6s. August 14:

that is to say, the wave took about 24h. 57m. to travel about 8,700

miles, which gives us an average rate of about 511 feet per second.

These waves were felt all over the Pacific. At the Chatham Islands they

rushed in with such violence that whole settlements were destroyed. At

the Sandwich Islands the sea oscillated at intervals of ten minutes for

three days.

Comparing this wave with the one of 1877 we see that one reached

Hakodate with a velocity of 511 feet per second, whilst the other

travelled the same distance at 512 feet per second.

An account of this earthquake wave has been given by F. von Hochstetter

(‘Über das Erdbeben in Peru am 13. August 1868 und die dadurch

veranlassten Fluthwellen im Pacifischen Ocean,’ Sitzungsberichte

der Kaiserl. Akademie der Wissenschaften, Wien 58. Bd., 2. Abth.

1868). From an epitome of this paper given in ‘Petermann’s Geograph.

Mittheil.’ 1869, p. 222, I have drawn up the following table of the

more important results obtained by F. von Hochstetter.

The wave is assumed to have originated near Arica.

+----------------+------------+----------+----------+----------+

+----------------+------------+----------+----------+----------+

| | | h. m. | | |

|Valdivia | 1,420 | 5 0 | 479 | 7,140 |

|Chatham Islands | 5,520 | 15 19 | 608 | 11,472 |

|Lyttleton | 6,120 | 19 18 | 533 | 8,838 |

|Newcastle | 7,380 | 22 28 | 538 | 9,006 |

|Apia (Samoa) | 5,760 | 16 2 | 604 | 11,346 |

|Rapa | 4,057 | 11 11 | 611 | 11,598 |

|Hilo | 5,400 | 14 25 | 555 | 9,568 |

|Honolulu | 5,580 | 12 37 | 746 | 17,292 |

+----------------+------------+----------+----------+----------+

Calculations on the same disturbance are also given by J. E.

Hilgard.[82]

Assuming the origin of the wave to have been at Arica, his results are

as follows:

+----------------+------------+------------+----------+----------+

+----------------+------------+------------+----------+----------+

|San Diego | 4,030 | 10 55 | 369 | 12,100 |

|Fort Point | 4,480 | 12 56 | 348 | 10,800 |

|Astoria | 5,000 | 18 51 | 265 | 6,200 |

|Kodiak | 6,200 | 22 00 | 282 | 7,000 |

|Rapa | 4,057 | 10 54 | 372 | 12,200 |

|Chatham Islands | 5,520 | 15 01 | 368 | 12,100 |

|Hawaii | 5,460 | 14 10 | 385 | 13,200 |

|Honolulu | 5,580 | 12 18 | 454 | 18,500 |

|Samoa | 5,760 | 15 38 | 368 | 12,100 |

|Lyttelton | 6,120 | 19 01 | 322 | 9,200 |

|Newcastle | 9,380 | 22 10 | 332 | 9,800 |

|Sydney | 7,440 | 23 41 | 314 | 8,800 |

+----------------+------------+------------+----------+----------+

_The wave of 1877._—Two sets of calculations have been made upon the

wave of 1877 by Dr. E. Geinitz of Rostock.[83]

The following table is taken from Dr. Geinitz’s second paper, in which

there are several modifications of his first results. The origin of the

disturbance is assumed to have been near Iquique.

+---------------------+--------+----------+-------+--------+--------+

+---------------------+--------+----------+-------+--------+--------+

| | | h. m. | h. m. | | |

| Islands) | 4,086 | 8 40 A.M.| 12 15 | 563·8 | 1,647 |

|Apia (Samoa) | 5,740 |12 0 „ | 15 30 | 610·4 | 1,930 |

|Hilo (Sandwich | 5,526 |10 24 „ | 14 0 | 667·9 | 2,310 |

|Kahuliu „ | 5,628 |10 30 „ | 14 5 | 675·2 | 2,361 |

|Honolulu „ | 5,712 |10 50 „ | 14 25 | 669·7 | 2,319 |

|Wellington (New | 5,657 | 2 40 P.M.| 18 15 | 524·2 | 1,430 |

|Lyttelton „ | 5,641 | 2 48 „ | 18 23 | 519·8 | 1,400 |

|Newcastle (Australia)| 6,800 | 2 32 „ | 18 7 | 633·0 | 2,075 |

|Sydney „ | 6,782 | 2 35 „ | 18 10 | 631·4 | 2,065 |

|Kamieshi (Japan) | 8,790 | 7 20 „ | 22 55 | 649·0 | 2,182 |

|Hakodate „ | 8,760 | 9 25 „ | 25 0 | 592·5 | 1,818 |

|Kadsusa „ | 8,939 | 9 50 „ | 25 15 | 604·9 | 1,895 |

+---------------------+--------+----------+-------+--------+--------+

The mean depths represent a mean of two sets of calculations, one

made with the aid of Airy’s formula, and the other by Scott-Russell’s

formula. The result of my own investigation about this disturbance, the

origin of which, by several methods of calculation, is shown to have

been beneath the ocean, near 71° 5′ west long., and 21° 22′ south lat.,

are given on next page.

Dr. Geinitz considers that his calculated depths of the ocean and those

obtained by actual soundings are in accordance, a result which is

diametrically opposed to that which I have obtained.

This difference between my calculations and those of Dr. Geinitz,

Hochstetter, and others, chiefly rests on the origin we have assigned

for the sea waves. Dr. Geinitz, for instance, although he says that

the origin of the 1877 earthquake was not on the continent but to the

west in the ocean, bases all his calculations on the assumption that

the _centrum_ was at or near to Iquique, and the time at which that

city was disturbed was the time at which the waves commenced to spread

across the ocean. This time is 8.25 P.M. At this time, however, it

appears that the waves must have been more than double the distance

between the true origin and Iquique, from Iquique on their way towards

the opposite side of the Pacific. Introducing this element into the

various calculations which have been made respecting the depth of the

Pacific Ocean as derived from observations on earthquake waves—which

element, insomuch as the waves appear to have come in to inundate the

land some time after the shock, needs to be introduced—we reduce the

velocity of transit of the earthquake wave and, consequently, the

resultant depths of the ocean.

Key:

A Distance from the origin in miles (calculated in great circles)

B Velocity in feet per second

+-----------+---------+---------+-----+-----+---+-------+--------+---------+

| |Longitude| in | by | A | B |ocean | of |waves in |

+-----------+---------+---------+-----+-----+---+-------+--------+---------+

| | ° ′ |day h. m.|h. m.| | | | | |

| of wave | 71 5 W.| 9 12 59| | | | | | |

|San | | | | | | | |

| Francisco|122 32 |10 2 28|13 29|4,578|498| 7,721 | 9 in. | |

|Callao | 77 15 | 9 17 9| 4 10| 658|231| 1,657 | | |

|Iquique | 70 14½ | 9 13 21| 0 22| 87|348| 3,770 | 20 ft. |22 |

|Cobija | 70 21 | 9 13 19| 0 20| 80|352| 3,857 | 30 „ | |

|Mejillones | 70 35 | 9 13 27| 0 28| 108|339| 3,587 | 35 „ |15 or 45 |

|Chanaral | 71 34 | 9 15 26| 2 27| 455|272| 2,309 | |10 |

|Coquimbo | 71 24 | 9 15 15| 2 16| 508|328| 3,363 | |30 |

|Valparaiso | 71 38 | 9 16 16| 3 17| 695|310| 3,000 | | |

|Concepcion | 73 5 | 9 16 52| 3 53| 928|350| 3,824 | |12 to 15 |

|Honolulu |157 55 |10 3 52|14 53|5,694|561| 9,807 |34 to |25 |

| | | | | | | | 54 ft.| |

|Hilo |155 3 |10 3 5|14 6|5,506|563|10,217 |30 or |{3 or 15 |

| | | | | | | | 8 „ |{18 or 27|

|Kahuliu |156 43 |10 3 12|14 13|5,611|579|10,437 | | |

|Samoa |171 41 W.|10 3 57|14 58|5,773|566| 9,972 | 12 ft. |10 |

|Taurauga |176 11 E.|10 8 15|19 16|5,615|427| 5,697 | | |

|Wellington |174 30 |10 7 22|18 23|5,574|445| 6,168 | 11 „ |10 |

|Akaroa |172 59 |10 7 28|18 29|5,542|440| 6,031 | | |

|Lyttelton |172 45 |10 7 29|18 30|5,558|441| 6,055 | | |

|Kameishi |140 50 |10 12 37|23 38|8,844|549| 9,378 | 6 „ |15 |

|Hakodate |140 50 |10 14 7|25 8|8,778|512| 8,169 | 7 „ |20 |

+-----------+---------+---------+-----+-----+---+-------+--------+---------+

In Dr. Geinitz’s paper there are also some slight differences in the

times at which the earthquake phenomena were observed at various

localities. These, however, are but of minor importance. At the end

of the paper by Dr. Geinitz two interesting tide gauge records are

introduced, one from Sydney and the other from Newcastle. These appear

to show a marked difference in the periods of the sea waves at these

two places.[84]

_Comparison of velocities of wave-transit which have been actually

observed, with velocities which ought to exist from what we know of

the depth of the Pacific by actual soundings._—From a chart given in

‘Petermann’s Geograph. Mittheilungen,’ Band xxiii. p. 164, 1877, it is

possible to draw approximate sections on lines in various directions

across the bed of the Pacific.

From the origin of the shock to Japan (Kameishi) the line would be as

follows:—

about 7,441 miles 15,000 feet deep

1,100 „ 18,000 „

160 „ 27,000 „

80 „ 12,000 „

60 „ 6,000 „

On account of the Tuscarora and Belkap Deeps this would be the most

irregular line over which the wave had to travel.

From the origin to New Zealand (Wellington) the line would be

about 5,274 miles 15,000 feet deep.

„ 300 „ 12,000 „

From the origin to Samoa the line would be

about 5,773 miles 15,000 feet deep.

From the origin to the Sandwich Islands (Honolulu) the line would be

almost 6,634 miles 15,000 feet deep

and 60 „ 12,000 „

By Scott-Russell’s rule, or, what is almost identically the same, by

Airy’s general formula, we can calculate how long it would take such

waves as we have been speaking about to travel over the different

portions of each of these lines, and by adding these times together we

obtain the time taken to travel across any one line. I have made these

calculations, but as I get in every case answers which are too small, I

think it unnecessary to give them.

The actual times taken to travel the distances just referred to were,

To Japan (Kameishi) 23 hr. 38 min.

„ New Zealand (Wellington) 18 „ 23 „

„ Samoa 14 „ 58 „

„ Sandwich Islands (Honolulu) 14 „ 53 „

From San Francisco to Simoda the line is almost 3,567 miles, 3,000

fathoms deep, 840 miles, 2,500 fathoms deep, and 120 miles 1,000

fathoms deep. This gives an average depth of about 2,854 fathoms. Bache

calculated the depth at 2,500 fathoms.

If we are to consider that, because the sea wave at Simoda came in

some time after the land shock had been felt, the origin of this

earthquake, instead of being at Simoda, was some distance out at sea,

this calculated depth would be reduced.