Fig. 5

Relationship between the two stress periods prior to the 2011 Tohoku earthquake and co- and post-seismic deformation of the M7 class earthquakes around Iwaki City. The relative difference between the NW–SE components of the GNSS time series at the two sites among the eight sites (a–h) near Iwaki City is plotted for the period from January 1, 2002, to March 1, 2011. Positive increases correspond to eastward movement. The eight stations for which we analyzed time series of GNSS data are: (a) 950,205; (b) 950,208; (c) 020,944; (d) 940,041; (e) 950,211; (f) 970,800; (g) 020,945; (h) 020,946; (i) 950,212; (j) 950,214. Five M7 class trench-type earthquakes with large post-seismic slips that occurred along the Japan Trench (Suito et al. 2011) are also marked: (A) August 16, 2005, Miyagi-ken Oki earthquake (Mj 7.2); (B) May 8, 2008, Ibaraki-ken Oki earthquake (Mj 7.0); (C) July 19, 2008, Fukushima-ken Oki earthquake (Mj 6.9); (D) March 14, 2010, Fukushima-ken Oki earthquake (Mj 6.7); and (E) March 9, 2011, Sanriku-Oki earthquake (Mj 7.3). Diamonds and stars on the inset map show the stations for the time series used in this study and epicenters of the five M7 class trench-type earthquakes, respectively. The rapid change in a–b (point *) is due to the maintenance of site 940,041. We do not discuss the rapid change in c–d (point †) in this study