Long‐period oceanic rayleigh wave group velocity dispersion curve from HF Doppler sounding of the ionosphere

Abstract

Earthquake‐generated Rayleigh waves excite shock waves at the surface of the earth which propagate upward nearly vertically through the atmosphere as infrasound. The HF Doppler sounder is a sensitive tool for detecting and recording these infrasounds at ionospheric heights. By constructing electron density distributions from ionograms the propagation ray paths and delay times for the long‐period waves can be determined. By using these data the dispersion curves for oceanic Rayleigh waves have been deduced. These curves are within 5% of the expected curve synthesized from data obtained from seismograms. Application of these data to the 1969 Kurile Island earthquake shows that it had a single source, while application to the 1968 Tokachi‐Oki earthquake shows the existence of several sources.