Institution: | Marine Geology Department, Geological Survey of Japan, 1-1-3 Higashi, Tsukuba 305-8567, Japan. E-mail:;, Department of Earth Sciences, Kumamoto University, Kumamoto 860-8555, Japan. E-mail: shibuya@ sci.kumamoto-u.ac.jp,;Air Force Technical Applications Center, Partrick AFB, FL 32925-3002, USA. E-mail: |