What causes earthquakes along fault lines?

Earthquakes along fault lines occur when tectonic plates grind against each other, releasing stored energy. Stress builds up as plates move slowly but are temporarily locked due to friction. When the stress exceeds the frictional resistance, the plates suddenly slip, causing the ground to shake. Faults like the San Andreas Fault in California are particularly active and prone to significant seismic events. The energy released during an earthquake travels as seismic waves, causing surface vibrations.