The Ground Roll Phenomenon of Applied Seismology

Citation

Gould, Martin James (1941) The Ground Roll Phenomenon of Applied Seismology. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/77xt-pm46. https://resolver.caltech.edu/CaltechTHESIS:12092020-212456873

Abstract

Since the preceding series of investigations are of a somewhat different character than the one to follow, it is desirable at this point to summarize the results so far obtained:

1. Gravitational waves in a viscous incompressible medium are far too slow to account for the velocity of first arrival of the ground roll.

2. The importance of Bateman's secondary Rayleigh wave cannot be known without the solution of the complex problem of the partition of energy at the source of the Rayleigh waves.

3. The theory of the propagation of Love waves on the surface of a layered visco-elastic medium indicates the possibility of velocities less than the shear wave velocity obtained without viscosity. The rapid damping of very short waves is also indicated. The possibility of obtaining a damping of the order of the ground roll damping has been demonstrated.

4. An examination of seismic data on the velocity of the ground roll has indicated that the observations are not necessarily inconsistent with the theory of dispersion of Rayleigh waves in a layered elastic medium, but, that there may be other causes of the observed dispersion.

Certain anomalous ground roll velocity variation near Fresno; California is possibly explanable on the hypothesis of dispersion in a layered elastic medium. For small values of L/H, the velocity of the ground roll agrees roughly with the velocity of Rayleigh waves, but these same velocities are associated with an initial anomalous forward cycle of the particle motion. Theoretically thereis an inherent disadvantage in obtaining dispersion data on the ground roll by seismic means, because of the factor of possible resonance making the interpretation of the results difficult. The three component ground roll data suggest the possible co-existence of Love waves and Rayleigh waves.

Thesis Files