Abstract: This invention provides a seismic joint for an underwater floating tunnel having: (a) a joint portion (i) having a transverse section essentially the same as that of the tunnel, (ii) being rigidly fastened to land at one end (A) thereof, and (iii) being elastically constrained to the tunnel at its other end (B) via a plurality of operably affixed means which performs an elastic function and a damping function; (b) a collar welded onto the external surface of the tunnel facing end (B) of the portion, said collar being capable of sliding on and along the external surface of the joint portion; and (c) a means for providing a water-tight seal between the internal surface of the collar and the external surface of the joint portion.