Ionoquakes: Earthquake precursors in the ionosphere?



The ionospheric literature is sprinkled with descriptions of phenomena observed near the site of future earthquakes. Any real connection, reliably established, clearly would be of practical value as well as of scientific interest, so the topic is worthy of debate.

Ionospheric effects following an earthquake have been well observed.They include large-scale waves, known as traveling ionospheric disturbances (TIDs),that travel thousands of kilometers. TIDs normally are launched by auroral disturbances in the highlatitude ionosphere or by storms and weather fronts in the lower atmosphere.Those observed on 28 March 1964 by sounders (ionosondes) in Alaska, California, and Hawaii [Leonard and Barnes, 1965] and Colorado [Davies and Baker, 1965] apparently originated earlier that day in the vicinity of the great Alaskan earthquake (M=9.2).Artru et al. [2001] have shown that seismic waves indeed can couple to the atmosphere.The reported ‘earthquake precursors’ are ionospheric phenomena recorded within a few hundred kilometers of the epicenter of a quake that occurred up to a few days later. The data come from ionosondes, of which about 100 worldwide make hourly records, and from instruments aboard orbiting satellites that happened to be passing near the site of the earthquake. Orbiting satellites offer global coverage, but their data are limited by the vagaries of orbits. Recently, precursors have been detected by monitoring the total ionospheric electron content along slant paths from radio transmitters on Global Position System satellites to a ground receiver.With its great advantages of continuity and wide geographic coverage, this technique deserves wider use.