5.4
IONOSPHERIC PRECURSORS OF THE 26 DECEMBER 2004 M9.3
SUMATRA EARTHQUAKE
1
Tiger J. Y. Liu1,2 and Y. I. Chen3
Institute of Space Science, Center for Space and Remote Sensing Research, and 3Institute of
Statistics, National Central University, Taiwan
2
jyliu@jupiter.ss.ncu.edu.tw
Large earthquakes are often preceded or accompanied by signals of different nature:
electric, magnetic, electromagnetic, or luminous, although seismic waves are the most
obvious manifestation. Recently, ionospheric phenomena occurred before earthquakes have
received considerable discussions. Of special interests are seismo-ionospheric precursors,
which appear a few days before large earthquakes. In this paper, we report seismoionospheric precursors of anomalous decreases in the total electron content (TEC) appearing
day 5 prior to an M9.3 earthquake, the largest one in the recent five decades, occurred in
Sumatra, Indonesia on 26 December 2004. Sequences of global ionosphere maps (GIMs) of
the TEC derived from worldwide ground-based receivers of the global positioning system
(GPS) are used to study signatures of the temporal and spatial precursors of the earthquake. It
is found that the temporal signature is that the GPS TEC around the epicenter significantly
reduces during the afternoon period on the precursor day. The spatial signatures demonstrate
that the precursor size is about 2500km and 5000km in radius from the epicenter in the
latitudinal and longitudinal direction, respectively.