Chapter I: Preface: • • • • •

In the following pages it has been my object to give a systematic account of various Earth Movements.

These comprise _Earthquakes_, or the sudden violent movements of the ground; _Earth Tremors_, or minute movements which escape our attention by the smallness of their amplitude; _Earth Pulsations_, or movements which are overlooked on account of the length of their period; and lastly, _Earth Oscillations_, or movements of long period and large amplitude which attract so much attention from their geological importance.

It is difficult to separate these Earth Movements from each other, because they are phenomena which only differ in degree, and which are intimately associated in their occurrence and in their origin.

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Because Earthquakes are phenomena which have attracted a universal attention since the earliest times, and about them so many observations have been made, they are treated of at considerable length.

As very much of what might be said about the other Earth Movements is common to what is said about Earthquakes, it has been possible to make the description of these phenomena comparatively short.

The scheme which has been adopted will be understood from the following table:—

I. EARTHQUAKES.

1. Introduction.
2. Seismometry.
{(_a_) Theoretically.
3. Earthquake Motion. {(_b_) As deduced from experiments.
{(_c_) As deduced from actual
Earthquakes.
4. Earthquake Effects. {(_a_) On land.
{(_b_) In the ocean.
5. Determination of Earthquake origins.
{(_a_) In space.
6. Distribution of Earthquakes. {(_b_) In time (geological time,
{ historical time, annual,
{ seasonal, diurnal, &c.)
7. Cause of Earthquakes.
8. Earthquake prediction and warning.

II. EARTH TREMORS.

III. EARTH PULSATIONS.

IV. EARTH OSCILLATIONS.

In some instances the grouping of phenomena according to the above scheme may be found inaccurate, as, for example, in the chapters referring to the effects and causes of Earthquakes.

This arises from the fact that the relationship between Earthquakes and other Earth phenomena are not well understood. Thus the sudden elevation of a coast line and an accompanying earthquake may be related, either as effect and cause, or _vice versâ_, or they may both be the effect of a third phenomenon.

Much of what is said respecting Earthquake motion will show how little accurate knowledge we have about these disturbances. Had I been writing in England, and, therefore, been in a position to make references to libraries and persons who are authorities on subjects connected with Seismology, the following pages might have been made more complete, and inaccuracies avoided. A large proportion of the material embodied in the following pages is founded on experiments and observations made during an eight years’ residence in Japan, where I have had the opportunity of recording an earthquake every week.

The writer to whom I am chiefly indebted is Mr. Robert Mallet. Not being in a position to refer to original memoirs, I have drawn many illustrations from the works of Professor Karl Fuchs and M. S. di Rossi. These, and other writers to whom reference has been made, are given in an appendix.

For seeing these pages through the press, my thanks are due to Mr. Thomas Gray, who, when residing in Japan, did so much for the advancement of observational Seismology.

For advice and assistance in devising experiments, I tender my thanks to my colleagues, Professor T. Alexander, Mr. T. Fujioka, and to my late colleague. Professor John Perry.

For assistance in the actual observation of Earthquakes, I have to thank my friends in various parts of Japan, especially Mr. J. Bissett and Mr. T. Talbot, of Yokohama. For assistance in obtaining information from Italian sources I have to thank Dr. F. Du Bois, from German sources Professor C. Netto, and from Japanese sources Mr. B. H. Chamberlain. For help in carrying out experiments, I am indebted to the liberality of the British Association, the Geological Society of London, the Meteorological and Telegraph departments of Japan, and to the officers of my own institution, the Imperial College of Engineering.

And, lastly, I offer my sincere thanks to those gentlemen who have taken part in the establishment and working of the Seismological Society of Japan, and to my publishers, whose liberality has enabled me to place the labours of residents in the Far East before the European public.

JOHN MILNE.

TOKIO, JAPAN; _June 30, 1883_

CONTENTS.

• • • • •

CHAPTER I.

INTRODUCTION.

PAGE
Relationship of man to nature—The aspect of a country
is dependent on geological phenomena—Earthquakes an
important geological phenomenon—Relationship of seismology
to the sciences and arts—Earth movements other than
earthquakes—Seismological literature—(Writings of Perrey,
Mallet, Eastern writings, the Philosophical Transactions of
the Royal Society, the ‘Gentleman’s Magazine,’ the Bible,
Herodotus, Pliny, Hopkins, Von Hoff, Humboldt, Schmidt,
Seebach, Lasaulx, Fuchs, Palmieri, Bertelli, Seismological
Society of Japan)—Seismological terminology 1

CHAPTER II.

SEISMOMETRY.

Nature of earthquake vibrations—Many instruments called
seismometers only seismoscopes—Eastern seismoscopes, columns,
projection seismometers—Vessels filled with liquid—Palmieri’s
mercury tubes—The ship seismoscope—The cacciatore—Pendulum
instruments of Kreil, Wagner, Ewing, and Gray—Bracket
seismographs—West’s parallel motion instrument—Gray’s conical
pendulums, rolling spheres, and cylinders—Verbeck’s ball and
plate seismograph—The principle of Perry and Ayrton—Vertical
motion instruments—Record receiver—Time-recording
apparatus—The Gray and Milne seismograph 12

CHAPTER III.

EARTHQUAKE MOTION DISCUSSED THEORETICALLY.

Ideas of the ancients (the views of Travagini, Hooke, Woodward,
Stukeley, Mitchell, Young, Mallet)—Nature of elastic waves
and vibrations—Possible causes of disturbance in the earth’s
crust—The time of vibration of an earth particle—Velocity
and acceleration of a particle—Propagation of a disturbance
as determined by experiments upon the elastic moduli of
rocks—The intensity of an earthquake—Area of greatest
overturning moment—Earthquake waves—Reflexion, refraction,
and interference of waves—Radiation of a disturbance 41

CHAPTER IV.

EARTHQUAKE MOTION AS DEDUCED FROM EXPERIMENT.

Experiments with falling weights—Experiments with
explosives—Results obtained from experiments—Relative
motion of two adjacent points—The effect of hills and
excavations upon the propagation of vibrations—The intensity
of artificial disturbances—Velocity with which earth
vibrations are propagated—Experiments of Mallet—Experiments
of Abbot—Experiments in Japan—Mallet’s results—Abbot’s
results—Results obtained in Japan 57

CHAPTER V.

EARTHQUAKE MOTION AS DEDUCED FROM OBSERVATION
ON EARTHQUAKES.

Result of feelings—The direction of motion—Instruments as
indicators of direction—Duration of an earthquake—Period
of vibration—The amplitude of earth movements—Side of
greatest motion—Intensity of earthquakes—Velocity and
acceleration of an earth particle—Absolute intensity of an
earthquake—Radiation of an earthquake—Velocity of propagation 67

CHAPTER VI.

EFFECTS PRODUCED BY EARTHQUAKES UPON BUILDINGS.

The destruction of buildings is not irregular—Cracks in
buildings—Buildings in Tokio—Relation of destruction
to earthquake motion—Measurement of relative motion of
parts of a building shaken by an earthquake—Prevention of
cracks—Direction of cracks—The pitch of roofs—Relative
position of openings in a wall—The last house in a row—The
swing of buildings—Principle of relative vibrational periods 96

CHAPTER VII.

EFFECTS PRODUCED UPON BUILDINGS (_continued_).

Types of buildings used in earthquake countries—In Japan,
in Italy, in South America, in Caraccas—Typical houses
for earthquake countries—Destruction due to the nature of
underlying rocks—The swing of mountains—Want of support
on the face of hills—Earthquake shadows—Destruction due
to the interference of waves—Earthquake bridges—Examples
of earthquake effects—Protection of buildings—General
conclusions 122

CHAPTER VIII.

EFFECTS OF EARTHQUAKES ON LAND.

1. Cracks and fissures—Materials discharged from
fissures—Explanation of fissure phenomena. 2. Disturbances
in lakes, rivers, springs, wells, fumaroles, &c.—Explanation
of these latter phenomena. 3. Permanent displacement of
ground—On coast lines—Level tracts—Among
mountains—Explanation of these movements 146

CHAPTER IX.

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 163

CHAPTER X.

DETERMINATION OF EARTHQUAKE ORIGINS.

Approximate determination of an origin—Earthquake-hunting
in Japan—Determinations by direction of motion—Direction
indicated by destruction of buildings—Direction
determined by rotation—Cause of rotation—The use of time
observations—Errors in such observations—Origin determined
by the method of straight lines—The method of circles, the
method of hyperbolas, the method of co-ordinates—Haughton’s
method—Difference in time between sound, earth, and water
waves—Method of Seebach 187

CHAPTER XI.

THE DEPTH OF AN EARTHQUAKE CENTRUM.

The depth of an earthquake centrum—Greatest possible depth of
an earthquake—Form of the focal cavity 213

CHAPTER XII.

DISTRIBUTION OF EARTHQUAKES IN SPACE AND TIME.

General distribution of earthquakes—Occurrence along
lines—Examples of distribution—Italian earthquake of 1873—In
Tokio—Extension of earthquake boundaries—Seismic energy in
relation to geological time; to historical time—Relative
frequency of earthquakes—Synchronism of earthquakes—Secondary
earthquakes 226

CHAPTER XIII.

DISTRIBUTION OF EARTHQUAKES IN TIME (_continued_) 234

CHAPTER XIV.

DISTRIBUTION OF EARTHQUAKES IN TIME (_continued_).

The occurrence of earthquakes in relation to the position of
the heavenly bodies—Earthquakes and the moon—Earthquakes
and the sun; and the seasons; the months—Planets and
meteors—Hours at which earthquakes are frequent—Earthquakes
and sun spots—Earthquakes and the aurora 250

CHAPTER XV.

BAROMETRICAL FLUCTUATIONS AND EARTHQUAKES—FLUCTUATIONS IN
TEMPERATURE AND EARTHQUAKES 266

CHAPTER XVI.

RELATION OF SEISMIC TO VOLCANIC PHENOMENA.

Want of synchronism between earthquakes and volcanic
eruptions—Synchronism between earthquakes and volcanic
eruptions—Conclusion 270

CHAPTER XVII.

THE CAUSE OF EARTHQUAKES.

Modern views respecting the cause of earthquakes—Earthquakes
due to faulting—To explosions of steam—To volcanic
evisceration—To chemical degradation—Attractive influence of
the heavenly bodies—The effect of oceanic tides—Variation in
atmospheric pressure—Fluctuation in temperature—Winds and
earthquakes—Rain and earthquakes—Conclusion 277

CHAPTER XVIII.

PREDICTION OF EARTHQUAKES.

General nature of predictions—Prediction by the observation of
unusual phenomena (Alteration in the appearance and taste of
springs; underground noises; preliminary tremors; Earthquake
prophets—warnings furnished by animals, &c.)—Earthquake
warning 297

CHAPTER XIX.

EARTH TREMORS.

Artificially produced tremors—Observations of Kater, Denman,
Airy, Palmer, Paul—Natural tremors—Observations of Zöllner,
M. d’Abbadie, G. H. and H. Darwin—Experiments in Japan—With
seismoscopes, microphones, pendulums—Work in Italy—Bertelli,
Count Malvasia, M. S. di Rossi—Instruments employed in
Italy—Tromometers, microseismographs, microphones—Results
obtained in Italy—In Japan—Cause of microseismic motion 306

CHAPTER XX.

EARTH PULSATIONS.

Definition of an earth pulsation—Indications of
pendulums—Indications of levels—Other phenomena indicating
the existence of earth pulsations—Disturbances in lakes and
oceans—Phenomena resultant on earth pulsations—Cause of earth
pulsations 326

CHAPTER XXI.

EARTH OSCILLATIONS.

Evidences of oscillation—Examples of oscillation—Temple of
Jupiter Serapis—Observations of Darwin—Causes of oscillation 344

APPENDIX 349

INDEX 359

EARTHQUAKES.

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