Earth Planets Space, Vol. 63 (No. 7), pp. 681-685, 2011
S. Hiratsuka and T. Sato
Department of Earth and Environmental Sciences, Hirosaki University, Hirosaki, Aomori, Japan
(Received April 5, 2011; Revised May 15, 2011; Accepted May 18, 2011; Online published September 27, 2011)
A giant earthquake of Mw 9.0 took place off the Pacific coast of Tohoku on March 11, 2011. It caused a large tsunami of 10-20 m and devastated the area along the Pacific coast in northeast Japan. The earthquake altered the stress field in the surrounding region immensely. We have calculated the change in Coulomb Failure Function (ΔCFF) due to this earthquake to evaluate the effect on aftershocks and future earthquake probabilities. The results suggest that the increased activity of normal-fault earthquakes after the main shock is explained by a large positive ΔCFF of 1-5 MPa prevailing over a vast area in and around the main-shock fault zone. The areas adjacent to the northern and southern borders of the fault zone where other large interplate earthquakes might occur are occupied by a positive ΔCFF of approximately 0.1 MPa. Based on the ΔCFF result, the future probability of reverse fault earthquakes in the shallow crust is estimated to be decreased in the land area of Tohoku.
Key words: 2011 Tohoku Earthquake, Japan Trench, great earthquake, ΔCFF, Coulomb Failure Function.