Earth Planets Space, Vol. 59 (No. 11), pp. e45-e48, 2007E-LETTER
Itoyuki Nishioka1, Minoru Funaki2, and Toshimori Sekine3
1The Graduate University for Advanced Studies, Hayama, Kanagawa 240-0193, Japan
2National Institute of Polar Research, Itabashi, Tokyo 173-8515, Japan
3National Institute for Materials Science, Tsukuba, Ibaraki 305-0044, Japan
(Received August 27, 2007; Revised October 3, 2007; Accepted October 9, 2007; Online published October 30, 2007)
Changes in the anisotropy of the low-field magnetic susceptibility (AMS) of basaltic andesite were induced by decaying stress waves and subsequently quantified. An initial shock pressure of 5 GPa was generated in a block of the target rock through impacting with a cylindrical projectile. Following the impact, the maximum or minimum principal susceptibility axes of the target were reoriented toward the shock direction at low (0.5-3 GPa) or high (>3 GPa) estimated shock pressures, respectively. Subtraction of the initial AMS demonstrated a parallelism between the induced susceptibility axes and the shock direction. These results suggest a potential application of AMS as an indicator of the propagation directions of stress waves generated in rocks at terrestrial impact structures.
Key words: Anisotropy of magnetic susceptibility, magnetic hardening, stress waves, basaltic andesite, impact crater.