Geophysical Research Letters publishes short, concise research letters that present scientific advances that are likely to have immediate influence on the research of other investigators.


Key Points
Positive TEC anomaly appears before M9 class events
The anomaly occurs above the epicenter and lasts ~1 hour
M9 class earthquakes can be predicted


Kosuke Heki
Department of Natural History Sciences, Hokkaido University, Sapporo, Japan


The 2011 March 11 Tohoku-Oki earthquake (Mw9.0) caused vast damages to the country. Large events beneath dense observation networks could bring breakthroughs to seismology and geodynamics, and here I report one such finding.

The Japanese dense network of Global Positioning System (GPS) detected clear precursory positive anomaly of ionospheric total electron content (TEC) around the focal region.

It started ∼40 minutes before the earthquake and reached nearly ten percent of the background TEC. It lasted until atmospheric waves arrived at the ionosphere.

Similar preseismic TEC anomalies, with amplitudes dependent on magnitudes, were seen in the 2010 Chile earthquake (Mw8.8), and possibly in the 2004 Sumatra-Andaman (Mw9.2) and the 1994 Hokkaido-Toho-Oki (Mw8.3) earthquakes, but not in smaller earthquakes.


Received 25 April 2011; accepted 25 August 2011; published 15 September 2011.