Fig. 4

Seismic and aseismic slip history along the plate interface prior to the Tohoku-Oki earthquake. a 1923–2002. Coseismic slip distributions of c. M > 7 interplate earthquakes [37,38] are shown by pink contours. b 2003 to January 2011. Coseismic slip distributions of c. M > 7 interplate earthquakes [1,37] are shown by pink contours. Aseismic slip from 2003 to January 2011 including postseismic slips after five c. M 7 events since 2003 [3] are shown by orange contours. c February 2011 to March 11, 2011. The slip area of an SSE that occurred in February [4] is shown by a rectangle of orange lines. The slip areas of the March 9 M 7.3 foreshock and of the postseismic slip [39] are shown by pink and orange ellipses, respectively. White contours represent the coseismic slip distribution of the Tohoku-Oki earthquake [3]. Hypocenters of events that occurred associated with the February SSE and with the M 7.3 foreshock [2] are shown by white and yellow circles, respectively. Red diamonds represent the locations of OBP gauge stations. The second and third stations from the trench axis are GJT3 and P09, respectively