Part I of this paper is devoted primarily to the presentation of the basic data of this investigation. As the data were obtained by the tripartite technique, a detailed discussion of the net used is included. From the data presented, it is readily apparent that:

  1. Free vibration in a “natural period” of the earth's crust in the vicinity of a recording station does not occur as a result of an earthquake at distance.

  2. Extensive wandering of the plane of polarization of seismic surface waves is due to variations in the azimuth of arrival of the surface waves.

  3. Surface waves arriving at Berkeley from a given earthquake do not have the nature of a continuous train of waves, but rather are characterized by the arrival of groups or packets composed of only a few periods. Thus the coda is not entirely a dispersion phenomenon but also has a scattered or refracted component. And

  4. Transverse motion does not exist in observed Rayleigh waves; apparent transverse motion is due simply to arrivals from other than the station-to-epicenter azimuth.

The detailed discussion of the basic data will be presented in Part II of this paper.

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