Earthquakes are caused by the sudden release of built-up energy in the Earth's crust. They can cause widespread damage through ground shaking and secondary effects like landslides and tsunamis. The document discusses the causes of earthquakes, different types of seismic waves, zones of seismic activity in India, and safety measures during and after an earthquake. It also summarizes the 2001 Bhuj earthquake in Gujarat, which had a magnitude of 7.7 and caused over 20,000 deaths through the destruction of infrastructure and homes. Proper construction techniques and early warning systems can help reduce risks from earthquakes.