Let me explain
The strait is about 4 km wide and up to about 110 metres deep, with about 1,400 ships passing every day. Huge foundations had to be built 60 metres under the sea in tidal currents of up to 4.5 metres per second, and the bridge was designed for winds of 80 metres per second and great earthquakes. In January 1995 a magnitude 7.2 earthquake struck after both towers were complete and changed the distance between them; engineers revised the length of the girder sections that had not yet been fabricated, and construction continued to completion after 10 years (Honshu-Shikoku Bridge Expressway, HSBE).