8:30 AM - 8:45 AM
[S11-1-01] TEC anomalies immediately before large earthquakes: Review and perspective
invited
Heki (2011) found ionospheric total electron content (TEC) enhancement starting ~40 min before the 2011 Mw9.0 Tohoku-oki earthquake. Heki & Enomoto (2015) confirmed similar phenomena before all the earthquakes in this century with Mw 8.5 or more. Critical papers claim that (1) the preseismic increase is an artifact popped up by defining the reference curves using the data after earthquakes, and (2) the anomalies originate from geomagnetic activities rather than earthquakes. In our rebuttals (Heki & Enomoto, 2013; 2014; 2015), we demonstrated statistical significance of the preseismic increases of vertical TEC rates. We also counted the occurrences of similar changes in TEC caused by space weather during times of no earthquakes and demonstrated it statistically unrealistic to attribute all the preseismic anomalies to space weather.
Recently, He and Heki (2016) analyzed the spatial distribution of preseismic TEC anomalies of 3 large earthquakes in Chile, i.e. the 2010 Maule, the 2014 Iquique, and the 2015 Illapel events. There, both positive and negative anomalies started simultaneously at altitudes of ~200 km and ~400 km, respectively, with 3-D structure similar to Kuo et al. (2014) predicted as the ionospheric response to positive electric charges on the ground.
We found three different Mw dependences of the anomalies so far. At first, the amount of the preseismic TEC rate changes are stronger for larger earthquakes and under higher background TEC. Secondly, larger earthquakes tend to have longer precursor times. Third, the anomalies of larger earthquakes have larger spatial dimensions. In the latest work, He and Heki (submitted) studied 32 earthquakes with Mw7.0-8.0 in this century, and found that 8 earthquakes showed possible preseismic changes starting 20-10 minutes before earthquakes. We could observe them before Mw7.0-8.0 earthquakes when background VTEC are large, say over 50 TECU.
Recently, He and Heki (2016) analyzed the spatial distribution of preseismic TEC anomalies of 3 large earthquakes in Chile, i.e. the 2010 Maule, the 2014 Iquique, and the 2015 Illapel events. There, both positive and negative anomalies started simultaneously at altitudes of ~200 km and ~400 km, respectively, with 3-D structure similar to Kuo et al. (2014) predicted as the ionospheric response to positive electric charges on the ground.
We found three different Mw dependences of the anomalies so far. At first, the amount of the preseismic TEC rate changes are stronger for larger earthquakes and under higher background TEC. Secondly, larger earthquakes tend to have longer precursor times. Third, the anomalies of larger earthquakes have larger spatial dimensions. In the latest work, He and Heki (submitted) studied 32 earthquakes with Mw7.0-8.0 in this century, and found that 8 earthquakes showed possible preseismic changes starting 20-10 minutes before earthquakes. We could observe them before Mw7.0-8.0 earthquakes when background VTEC are large, say over 50 TECU.