Tatsuya Mizuta¹, *Tomomi Okada¹, Martha Savage², Ryota Takagi¹, Keisuke Yoshida¹, Shinichi Sakai³, Kei Katsumata⁴, Mako Ohzono^4,3, Masahiro Kosuga⁵, Takuto Maeda⁵, Yoshiko Yamanaka⁶, Hiroshi Katao⁷, Takeshi Matsushima⁸, Hiroshi Yakiwara⁹, Takashi NAKAYAMA¹, Satoshi Hirahara¹, Toshio Kono¹, Toru Matsuzawa¹, Group for the aftershock observations of the 2011 off the Pacific coast of Tohoku Earthquake (1.Research Center for Prediction of Earthquakes and Volcanic Eruptions, Graduate School of Science, Tohoku University, 2.Victoria University of Wellington, 3.ERI, University of Tokyo, 4.Hokkaido University, 5.Hirosaki University , 6.Nagoya University, 7.DPRI, Kyoto University, 8.Kyushu University, 9.Kagoshima University)