Question

What effect might an earthquake along this fault have on a river that runs perpendicular to the fault

Answer 1

Underground, at the point where slippage along the fault begins.

Answer 2

Answer: In case of a river that is flowing over a fault in a perpendicular manner, if earthquake triggers, then it will be affecting the block in such a way that one block will move up whereas the other block will move down.

                              Due to this shifting of the block, the river channel will also experience an abrupt change in its gradient. The steepness of the river at that point will increase or the river level may also get shrink to a certain extent.