1. Dept. of Natural Sciences and Mathematics, National Chiayi Teachers College, Chiayi City, Taiwan, R.O.C. and Allied Geophysical Laboratories, University of Houston, Houston TX 77204-4231
2. Dept. of Geology and Geophysics, Rice University, Wiess School of Natural Sciences, P.O. Box 1892, Houston, TX 77251
3. Allied Geophysical Laboratories, University of Houston, TX 77204-4231