What causes stress?

So far we understand that there are different types of earthquakes, caused by forces under the Earth's crust that change the shape of the material they are acting on, and produce a variety of waves which we feel. But what are these forces? Where do they occur? What causes them?

The explanation for the majority of earthquakes in recent years falls under the category of plate tectonics. When two plates interact at their boundaries they put forces on each other. These forces of reaction cause physical and chemical changes at their boundaries. Plates move side to side, up and down, and also interact head on. Earthquakes also occur in these areas where new plates are being created and old plates are being subducted into the Earth's interior. Earthquakes which are due to the interaction of plates are called interplate earthquakes. But what about intraplate earthquakes, which occur across one plate? Less common than earthquakes that occur at plate boundaries, these earthquakes are due to local systems of forces, such as lack of strength or changes in temperature below the Earth's crust. Most often they are due to movement on pre-existing faults.

What are earthquakes? Types of earthquakes Forces What causes stress? Elasticity Waves Detection and recording Measurement A new type of measurement