Here's why:

* Seismic Activity: Seismic belts are areas where the Earth's crust is particularly active, with frequent earthquakes.

* Plate Boundaries: These belts coincide with plate boundaries, where tectonic plates interact. These interactions cause stress and strain, leading to earthquakes.

* Mapping Earthquakes: By plotting the locations of earthquakes, we can identify these zones of concentrated seismic activity.

So, in short, seismic belts are mapped by pinpointing the locations of earthquakes, which in turn reveals the zones of intense tectonic activity along plate boundaries.