Fracture Analysis of Hilina Slump, Nuuanu and Wailau Debris Avalanches, Hawaii: Transport Mechanism and Comparison with Subaerial Analogues 2. Fracrtal Analysis

Shinji Takarada, Tadahide Ui, James.G. Moore, Julia Morgan, Peter W. Lipman, Kenji Satake, John Smith, Nohiro Tsuboyama, Mario Yoshida, Mitsuhiro Yoshimoto and Daisuke Miura

American Geophyical Union, Western Pacific Geophysics Meeting, Tokyo, 12.6

　More than 15 giant submarine debris avalanche deposits are distributed around Hawaii islands. One of the largest (>5000 km³) Nuuanu-Wailau debris avalanche deposits northeast offshore of Oahu were investigated using submersible Kaiko and Shinkai 6500, JAMSTEC in 1998 and 1999. Hilina slump at southwest offshore of Hawaii island, creeping <10 cm/year, possible future giant submarine debris avalanche was also investigated. To reveal emplacement mechanism and depositional features of giant submarine debris avalanches, crack numbers per meter and fractal dimensions of pervasive jigsaw cracks in the Nuuanu-Wailau deposits and the Hilina slump were analyzed. Video and still camera images of Dive K90, K91, K93, K95, and K98 by the Kaiko in 1998 and 6K496-511 by the Shinkai 6500 in 1999 were used for analysis. The numbers of jigsaw cracks per meter in the Nuuanu-Wailau debris avalanche deposits were 8-16 and that of Hilina slump were 30-32. The fractal dimensions were caluculated by box counting method using the NIH-image software. The fractal dimensions of the Nuuanu-Wailau debris avalanche deposits were 1.60-1.63 and that of the Hilina slump were 1.66-1.67. The higher value of crack number and fractal dimensions of cracks within the Hilina slump than the Nuuanu-Wailau debris avalanche deposits may indicate different origin such as tectonic and cooling joints. The crack number and the fractal dimension of subaerial Zenkoji debris avalanche deposit, Usu volcano, Japan were 24/m and 1.61, respectively, indicating similar value of submarine Nuuanu-Wailau debris avalanche deposits.