From the AGU: An atmospheric precursor to the recent Japan megaquake
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 detects 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 percent above the background electron content. The increase in TEC was greatest above the earthquake epicenter and diminished with distance from the epicenter. The researcher also analyzes GPS records from previous earthquakes and finds that similar ionospheric anomalies occurred before the 2010 magnitude 8.8 Chile earthquake, possibly the 2004 Sumatra magnitude 9.2 earthquake, and possibly the 1994 magnitude 8.3 Hokkaido earthquake, but TEC enhancements were not seen before smaller earthquakes.
Figure 4 Total Electron Current (TEC) with time of earthquake events
Although previous studies have shown that earthquakes could trigger atmospheric waves that travel upward and disturb the ionosphere, it is unclear how an ionospheric disturbance could occur before an earthquake begins. In addition, the ionosphere is highly variable, and solar storms can trigger large TEC changes, so nonearthquake causes of any TEC enhancement need to be ruled out. The researcher states that, unlike previously suggested earthquake precursors, the TEC enhancement before the Tohoku quake had obvious spatial and temporal correlation between the quake and precursor signal as well as clear magnitude dependence. Further research is needed to verify that TEC enhancements can indeed be a precursor to large earthquakes.
Source: Geophysical Research Letters, doi:10.1029/2011GL047908, 2011 http://dx.doi.org/10.1029/2011GL047908
Title: Ionospheric electron enhancement preceding the 2011 Tohoku-Oki earthquake
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
Abstract
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.
