| dc.description.abstract | ii
In this dissertation, the ionospheric maximum plasma frequency, foF2,
is applied to study ionospheric variations before the 3 strong Rei-Li, Chi-
Chi, and Chia-Yi earthquakes. Results show that the foF2 signatures
decrease before the three-earthquake onset. Meanwhile, the ionospheric
total electron content (TEC) observed by the global positioning system
(GPS) receivers in Taiwan area is also utilized to investigate these events.
It is found that the equatorial anomaly crest of the GPS TEC moves
equatorward and the associated TEC value significantly decreases 1-4
days before the three earthquakes. Further, the foF2 before fourteen
M³6.0 earthquakes occurred in 1994-1999. It is found that the
decreases appear at 1200-1700LT within 6 days before the onset of the
earthquakes, and most likely appear 1 day before. On the other hand, a
comparison between the day-to-day variability and anomalies in the foEs
before the fourteen M³6.0 earthquakes shows that the foEs severly
enhances during the sunrise and sunset periods. Further, a robust
statistical technique is applied to identify anomalies in the foF2 appearing
in the Taiwan area during 184 M³5.0 earthquakes occurred in 1994-1999.
A stacking process and cross correlation analyses have uncovered not
only the typical shape foF2 decreasing 1200-1700LT, but also the leading
time 1-5 days the ionospheric precursors. Furthermore, simulation tests
verify the superiority of the ionospheric precursor over a seismicity-based
prediction process and confirm the significance of the ionospheric
precursor related to the earthquakes. The statistics results show that the
probabilities of observing the features 1-5 days prior to the forthcoming
shocks is 74.1% and, on the other hand, the valid alarm rate of the
ionospheric precursor is 53.3%. | en_US |