As the crust of the San Andrea is continuously moving due to the tectonic activity and is the main manifest of the tectonic boundary of the North America and the pacific plate. This fault along with the pacific plate will move towards the Los angles and eastern San Francisco as it moves about 3.5 cm per year.
As 1 km equals to about 100 000 cm
, then the distance of 620 km = 62, 000,000 cm and 62,000,000 will be divided by 3.5 equal to 17. 71 years to collide with the eastern side.