Acknowledgement The foF2, GPS data, and the earthquake catalog are obtained from the
Chung-Li station, the Ministry of Interior and the Central Weather Bureau of Taiwan,
respectively. This research was supported by the Ministry of Education under Grant 91-NFA07-
7-4 for the iSTEP project of the National Central University. The authors wish to thank
the reviewers for their useful comments and suggestions which significantly improve the presentation
of this paper.