The correct answer is option 3: Collision of earth plates. Earthquakes typically occur when there is a release of energy in the Earth`s crust. It is primarily caused by the collision or movement of tectonic plates. The Earth`s crust is divided into several large and small plates that are constantly moving. When two plates collide or slide past each other, they can create tension and pressure. Eventually, this pressure is released in the form of seismic waves, resulting in an earthquake. Eustatic movement (option 1) refers to global changes in sea level, which is unrelated to earthquakes. Isostatic adjustment (option 2) pertains to the vertical movement of Earth`s crust due to the redistribution of loads, and it is not directly associated with the occurrence of earthquakes. While volcanic eruptions (option 4) can cause earthquakes, they are not the primary cause of devastating earthquakes.