Earth Planets Space, Vol. 63 (No. 7), pp. 655-658, 2011
National Research Institute for Earth Science and Disaster Prevention, 3-1 Tenno-dai, Tsukuba, Ibaraki, Japan
(Received April 9, 2011; Revised May 9, 2011; Accepted May 10, 2011; Online published September 27, 2011)
The 2011 off the Pacific coast of Tohoku Earthquake was an unexpected megathrust event with magnitude 9.0 along the Japan trench. Hi-net tilt records prior to the great earthquake are examined in order to determine whether a precursory tilt change is observed in the short-term (∼days) and medium-term (∼a month) for confirming a preslip hypothesis and the effectiveness of an earthquake prediction method based on that hypothesis. For a quantitative reference to the observation, the detectability of the tilt observation for interplate slip on the subducting Pacific plate is also evaluated. In this study, no clear signal of preseismic tilt change or preslip is found in the records. This means that there is no preslip larger than moment magnitude (Mw) 6.2 on the deeper extension of the earthquake source area on the plate interface or larger than Mw 7.3 near the hypocenter.
Key words: Preseismic crustal deformation, preslip, earthquake prediction, NIED Hi-net.