Amplitude spectral density of the ambient earth motion in the vertical and horizontal directions at a quiet site are given in graphical and tabular form over the five decades of period from 0.1 to 2560 sec. Comparison of these spectra in the period range between 0.1 and 3 sec with the Brune and Oliver (1959) minimum curve and in the period range between 10 and 100 sec with spectra from the mines at Las Cruces, New Mexico, and Ogdensburg, New Jersey, indicate that in these period ranges the spectra are representative of the quietest seismograph stations presently known. These spectra can serve as a guide for seismologists and other scientists interested in the quiescent vibrations of the ground.

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