Earth Planets Space, Vol. 58 (No. 12), pp. 1577-1580, 2006LETTER
Naoki Uchida, Toru Matsuzawa, Satoshi Hirahara, and Akira Hasegawa
Research Center for Prediction of Earthquakes and Volcanic Eruptions, Graduate School of Science, Tohoku University, Sendai 980-8578, Japan
(Received February 27, 2006; Revised May 16, 2006; Accepted October 12, 2006; Online published February 2, 2007)
Taking advantage of the feature that creep around an asperity is necessary for the recurrent rupture of the same small asperity (small repeating earthquakes), we have estimated the spatio-temporal distribution of quasistatic slip (creep) around the 2005 Miyagi-oki earthquake (M=7.2) using the distribution of small repeating earthquakes. The creep was detected mainly outside of the coseismic slip areas for the 2005 Miyagi-oki, 1978 Miyagi-oki (M=7.6) and 2003 Fukushima-oki (M=6.8) earthquakes. The creep rates estimated from the recurrence intervals and slip amounts of small repeating earthquakes for 21 years were almost constant for the areas near the western limit of the interplate earthquakes but they varied temporally in the areas nearer to the Japan trench. The changes in the creep rates before and after the 2005 Miyagi-oki earthquake were not significant with the exception of small slip accelerations in some areas near the Japan trench. These results suggest that the plate boundary around the source area for the 2005 earthquake is still mostly locked.
Key words: Repeating earthquake, asperity, slow slip, subduction zone, interplate earthquake.