Ionospheric effects observed around the time of the Alaskan earthquake of March 28, 1964

The purpose of this note is to draw attention to certain ionosperic disturbances observed near certain ionospheric disturbances observed near Boulder, Colorado, around the time of the Alaskan earthquake, which occurred at about 0335 UT, March 28, 1964. These ionospheric observation consisted of the spectral analysis of ionospherically propagated radio signals by the method of Watts and Davies [1960]. Observation were made at Boulder on frequencies of 4 and 5 Mc/s, with vertical propagation, and on 10 Mc/s from WWVH in Hawaii, about 5000 km from Boulder. The frequency versus time records are shown in Figure 1. The WWVH 10-Mc/s signal and reflected from the ionosphere by a normal refractive process, whereas, after about 0130 UT, the Boulder 5-Mc/s signal appears to have been scattered by ionospheric irregularities, as can be seen in the ionogram in Figure 2, in which the penetration frequency of the extraordinary wave is less than 5 Mc/s.