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Annales Geophysicae An open-access journal of the European Geosciences Union
Ann. Geophys., 35, 589-598, 2017
https://doi.org/10.5194/angeo-35-589-2017
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.
Regular paper
25 Apr 2017
Seismo-ionospheric anomalies in ionospheric TEC and plasma density before the 17 July 2006 M7.7 south of Java earthquake
Dan Tao1, Jinbin Cao1, Roberto Battiston2, Liuyuan Li1, Yuduan Ma1, Wenlong Liu1, Zeren Zhima1, Lanwei Wang3, and Malcolm Wray Dunlop1 1Space Science Institute, School of Space and Environment, Beihang University, Beijing, China
2Dipartimento di Fisica, Università di Trento, Trento, Italy
3Institute of Crustal and Dynamics, China Earthquake Administration, Beijing, China
Abstract. In this paper, we report significant evidence for preseismic ionospheric anomalies in total electron content (TEC) of the global ionosphere map (GIM) and plasma density appearing on day 2 before the 17 July 2006 M7.7 south of Java earthquake. After distinguishing other anomalies related to the geomagnetic activities, we found a temporal precursor around the epicenter on day 2 before the earthquake (15 July 2006), which agrees well with the spatial variations in latitude–longitude–time (LLT) maps. Meanwhile, the sequences of latitude–time–TEC (LTT) plots reveal that the TECs on epicenter side anomalously decrease and lead to an anomalous asymmetric structure with respect to the magnetic equator in the daytime from day 2 before the earthquake. This anomalous asymmetric structure disappears after the earthquake. To further confirm these anomalies, we studied the plasma data from DEMETER satellite in the earthquake preparation zone (2046.4 km in radius) during the period from day 45 before to day 10 after the earthquake, and also found that the densities of both electron and total ion in the daytime significantly increase on day 2 before the earthquake. Very interestingly, O+ density increases significantly and H+ density decreases, while He+ remains relatively stable. These results indicate that there exists a distinct preseismic signal (preseismic ionospheric anomaly) over the epicenter.

Citation: Tao, D., Cao, J., Battiston, R., Li, L., Ma, Y., Liu, W., Zhima, Z., Wang, L., and Dunlop, M. W.: Seismo-ionospheric anomalies in ionospheric TEC and plasma density before the 17 July 2006 M7.7 south of Java earthquake, Ann. Geophys., 35, 589-598, https://doi.org/10.5194/angeo-35-589-2017, 2017.
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Short summary
We report significant evidence for pre-seismic ionospheric anomalies in total electron content (TEC) of a global ionosphere map (GIM) and plasma density and temperature appearing on day 2 before the 17 July 2006 M7.7 south of Java earthquake. The LTT spatial analysis also reveals a new feature: the TECs on epicenter side anomalously decrease and lead to an anomalous asymmetric structure with respect to the magnetic equator starting from day 2 before and disappearing after the earthquake.
We report significant evidence for pre-seismic ionospheric anomalies in total electron content...
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