On Some Problems Concerning the Seismic Field Methods

The periods of longitudinal waves produced by explosions increase with distance in a similar way as earthquake waves (equation 1). The amplitudes of the waves (equation 1) depend not only on the amount of energy reflected or refracted at discontinuities, but also on the angle of incidence at the instruments and its rate of change with distance. Calculations on the relative amplitudes of direct, reflected and refracted waves (Fig. 1) are in agreement with the observations. Formulae are given to calculate the approximative dip of discontinuities using either the distance at which the travel time of the reflected wave is a minimum or the difference in travel time between two instruments, especially at two opposite sides of the shot point, or the direction of the travel time curve at the shot point. The surface waves (ground roll) recorded from explosions can hardly be pure elastic waves; their velocity is too small for either Love- or Rayleigh-waves

Periods of the Ground in Southern California Earthquakes

From the early seismic records various Japanese scientists found that the microseisms which are produced by traffic, industry, and meteorological conditions, as storms and surf, show certain prevailing periods which are different in different localities. Omori and Kikuchi have especially investigated this problem. Kikuchi expressed his opinion that the prevailing periods constituted the free periods of the ground and their harmonics. The problem of the connection between periods of microseisms produced by local causes and the free periods of the ground has been investigated frequently since. O. Geussenhainer in his investigation of microseisms in Göttingen with periods between 5 and 9 seconds found that they change gradually in the course of time in the vertical component, but that in the horizontal component periods of 6, 7.5, and 9 seconds prevail. He believed these periods to be free periods of Love waves in the ground near Göttingen or harmonics of such

On Seismic Waves (Third Paper)

In two previous papers under the present title 1) 2) the authors have presented data on bodily waves. The present paper contains the corresponding data on surface waves (including seismic sea waves), the magnitude and energy of earthquakes, and miscellaneous topics. The seismograms used were those studied in the previously published investigations; the numbers assigned to individual shocks are as given in the previous papers

On Seismic Waves (Second Paper)

In a first paper under the present title the authors have presented a body of data on travel times. The present paper contains the corresponding data on amplitudes, periods, velocities, etc., for bodily waves. It is intended to present data on surface waves in a third paper

Erde (physikalische Beschaffenheit)

1. Aufbau der Erde. 2. Dichte und Masse der Erde. 3. Druck im Erdinnern. 4. Schwere, Lotabweichungen, Isostasie. 5. Die Righeit im Erdinnern. 6. Die Kompressibilität des Erdinnern. 7. Die innere Reibung im Erdinnern. 8. Die Viskosität im Erdinnern und der Fließwiderstand. 9. Abkühlung und Temperatur der Erde. 10. Kräfte im Erdinnern. 11. Bewegungen einzelner Teile der Erde

Tsunamis and earthquakes

Strong earthquakes occurring near an oceanic coast are sometimes followed by alternating advances and recessions of the sea, which may even rush inland several kilometers over beaches, carry ships ashore, crush houses, then recede far beyond the normal shore, and in repeated oscillations cause great damage and loss of life. In the open ocean, these waves are of so great length that they are not dangerous. In general, their period is between a quarter- and a half-hour; their velocity in an ocean of the constant depth h is approximately √gh. This gives about 220 m/sec, in water 5 km. deep, and about 70 m/sec, in water 500 m. deep; the corresponding lengths of waves with a period of 30 min. are about 400 km. and 130 km., respectively