Additional file 20: of Spatio-temporal changes in the seismic velocity induced by the 2011 Tohoku-Oki earthquake and slow slip event revealed from seismic interferometry, using ocean bottom seismometer’s records

Temporal variations in 15-day ACFs at Station S15. (a) 15-day ACFs calculated from OBS data over 15 continuous days, including the 7 days before and after the given date. The ACFs plotted in red are in the SSE period, and the bottom ACF is the reference ACF, calculated for the month from November 19 to December 19. (b) The cross-correlation coefficient between the 15-day ACFs and the reference ACF, using a 15 s time window and zero lag time. The period between the black triangles corresponds to the SSE period, and the periods between the red, blue, and green triangles correspond to low-frequency tremor periods in Sequences 1, 2, and 3. The magenta broken line represents the main shock. (c) Phase variation in the 15-day ACFs relative to the reference ACF, using a 15 s time window. Warm colors represent phase progressions, and cold colors represent phase delays. The four pairs of triangles and the magenta broken line correspond to each period and the main shock described in (b). (PDF 1911 kb)