Hi Shan. It is my understanding that radio interference did occur on the lower side of an AM stations near the area of the Loma Prieta quake in 1989.

The following is from a link in Japan in which radio interference was noted, but in a much different way just before the Kobe quake in 1995. Take Care…Don in creepy town

"In 1993, we started the meteor counting by observing the radio echoes in the very-high-frequency (VHF) band using a commercially provided FM receiver set. Radio echo is observed as a pulsed delivery of radio waves from a radio station located beyond the line of sight, which typically continues for hundreds of milliseconds. The radio waves are delivered by specular reflection on plasma tubes generated in the ionosphere on the passage of meteors through the atmosphere.

We recorded the time variation of radio wave intensity using a chart recorder. Radio echoes were recorded as sharp spikes on a baseline. We sometimes observed an anomalous behavior of the baseline. By the end of 1994, we empirically recognized that such an anomalous behavior appeared a few days before the earthquakes occurred between our observatory and the radio station tuned by the receiver set. We, however, did not pay enough attention to the possible correlations between earthquakes and anomalies in radio observation until the Hyogo-Nanbu Earthquake (M7.2) occurred on 17 January 1995. The detection of radio echoes became difficult due to extraordinary baseline fluctuations, which reached its maximum value on the night of 14 January 1995. The baseline fluctuation gradually returned to the usual level about 20 days after the earthquake. We learned that such extraordinary anomalies were also observed by amateur astronomers and that civilians in the seismic region experienced large noises in receiving radio programs, which motivated us to extend our radio observation. After we carried out preliminary observations during February to April 1995, we increased the number of receiver sets and initiated continuous monitoring of baseline behavior to study a possibility of earthquake forecasting using radio observation in the VHF band."

• Radio Interference