Most scientists believe that earthquakes are inherently unpredictable, and reports of various kinds of earthquake precursor signals have been difficult to verify. However, in a new study, Heki reports a possible ionospheric precursor to the devastating 11 March 2011 magnitude 9 Tohoku earthquake in Japan. Analyzing data from the Japanese GPS network, he detected an increase in the total electron content (TEC) in the ionosphere above the focal region of the earthquake beginning about 40 minutes before the quake. The TEC enhancement reached about 8% above the background electron content. The increase in TEC was greatest above the earthquake epicenter and diminished with distance from the epicenter. The author also analyzed GPS records from previous earthquakes and found that similar ionospheric anomalies occurred before the 2010 Mw 8.8 Chile earthquake and possibly the 2004 Sumatra Mw 9.2 earthquake and the 1994 Mw 8.3 Hokkaido earthquake, but TEC enhancements were not seen before smaller earthquakes.