Can HAARP cause an earthquake?

For the same place, yes, it is possible. This does not usually occur though, because most earthquakes will die off after a few minutes followed only by aftershocks. Once an earthquake occurs it...

Yes. The actions of people can cause earthquakes with detonation of explosives or nuclear weapons.

Izmit is built on a fault, and the two plates slid under each other and caused the earthquake.

Earthquakes are caused by the movement of tectonic plates under the Earth's surface. When these plates move and overlap each other then a lot of moovement is produced which results in an earthquake....

the underground plates shifting an causing the ground to shake witch people cause an earthquake