On the precursors to the 2011 Tohoku earthquake: crustal movements and electromagnetic signatures

We compare the precursory behaviour of crustal movements with electromagnetic signatures for the 2011 off the Pacific Coast of Tohoku earthquake. First, we present the Global Positioning System (GPS) data on the co-seismic variations and pre-seismic precursors (medium-term, short-term and imminent precursors). Then, we will review recently published results on electromagnetic precursors, including mainly short-term subionospheric very low frequency (VLF)/LF propagation anomaly, ultralow frequency (ULF) magnetic field depression and ULF/extremely low frequency (ELF) atmospheric radiation. Finally, we examine the relationship between the crustal movements and electromagnetic phenomena. We conclude that at least short-term electromagnetic precursors are closely correlated in time with the corresponding crustal movements. This seems to provide evidence on the link between lithospheric and electromagnetic processes. Some discussions will be given on the possible mechanism of this link