Propagation anomaly of oversea VHF waves possibly associated with earthquakes

Broadband spectra in the VHF band are observed to investigate any anomaly of propagation of distant TV broadcasting waves. We concluded that Malaysia and Philippines TV waves at lower frequencies are refracted by the F2 layer in the daytime ionosphere. We found that TV waves from Malaysia at 48.25 MHz were sometimes heavily attenuated for a few hours when earthquakes occur in the Okinawa area. We propose a hypothesis that the attenuation is caused by some disturbance in the ionospheric E layer above epicenters. Results of computer simulations suggest that a 10% enhancement or depletion of electron densities can explain the observed attenuation.