Earthquakes and other earth movements — A Closer Reading

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

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

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

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

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

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

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

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

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

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

THE DEPTH OF AN EARTHQUAKE CENTRUM.

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

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

DISTRIBUTION OF EARTHQUAKES IN TIME (_continued_) 234

DISTRIBUTION OF EARTHQUAKES IN TIME (_continued_).