Did the Miyako earthquake affect Medium Wave broadcast reception on 9 November 2025?

In early November 2025, a group of DXers in northern Japan observed a sharp but temporary attenuation of signal strengths of a number of medium wave broadcast signals in Japan and in northeast China. Within one-half hour, a major earthquake was felt at the listening site. Speculation arose as to whether there could be any connection between the two events. SDR recordings of the entire medium wave band were available from throughout this period, and it was possible to carefully analyze changes in strength of the attenuated signals over time. In addition, by examining the geographic spread of the locations of the transmitters associated with those signals, it was concluded that there was no obvious connection between the earthquake and the observed attenuation. Further investigation revealed that a large solar flare had occurred at the same time as the attenuation. Despite solar flares not normally being perceived as an influence on propagation at medium frequencies because of already existing daytime D-region attenuation, it was found that the progress of the solar flare correlated well with the progress of both the decay and the recovery of the observed signal strengths.