No. 27: May-Jun 1983
March 31, 1980. Tokyo, Japan. Anomalously high electromagnetic noise was recorded during a 30-minute period preceding a magnitude 7 quake, 250 km away and 480 km deep. The emissions were detected between 10 and 1500 Hz and around 81 kHz.
July 24-28, 1976. Tangshan, China. For 3-5 days before the Tangshan earthquake, unusual radio interference was experienced within 250 km of Tangshan.
Several similar cases are also on record, including one in which the radio noise coincided with the appearance of earthquake lights. No generally accepted physical mechanism for producing these electromagnetic emissions has been found.
(King, Chi-Yu; "Electromagnetic Emissions before Earthquakes," Nature, 301:377, 1983.)