Seismic activity refers to the vibrations and movements of the Earth's crust caused by the release of energy from tectonic plates. This energy can result in events such as earthquakes, which are sudden shaking of the ground, and aftershocks, which are smaller tremors that follow the main event. Seismic activity is measured using instruments called seismometers, which detect and record the intensity and duration of these movements. Scientists study seismic data to understand the behavior of fault lines and to assess the risk of future seismic events in different regions.