[J06-P] Poster

[J06-P-08] Slip velocities of early afterslips in northeastern Japan

^○Shunsuke Morikami, Yuta Mitsui (Shizuoka University, Shizuoka, Japan)

We focus on temporal evolution of early afterslip velocities following large interplate earthquakes (2003 Tokachi-oki, 2005 Miyagi-oki, 2011 Tohoku-oki (March 9), and 2011 Tohoku-oki (March 11)) in northeastern Japan. First, we obtain surface deformation data at an interval of 30 seconds about 2 days after the earthquakes, using GSILIB. Next, we invert slip velocities at the plate interface from the data. We find that initial velocities of the afterslips positively correlate with magnitude of the mainshocks. The initial afterslip velocities are four orders of magnitude lower than mean slip velocities of their mainshocks. The early afterslips decay almost linearly with time during the investigation periods. Besides, we check effects of viscoelastic relaxation of asthenosphere by a numerical simulation, and confirm that the viscoelastic relaxation effects are negligible during the investigation periods in a viscosity range larger than 10^18 [Pa s].