What is the source of beach sediment?

Beaches are always comprised of sands and this sands are derived from the terrestrial rocks, that are transported to the beaches by the rivers and steams, getting accumulated at the coastal region.

The ocean waves also continuously erodes the rocks of coastal region which ultimately leads to the total composition of sand.

The finer sand particles are often carried by the waves towards the ocean and only the coarser sands remains which are temporarily present and soon will be washed away.

The sea sands are comprised of salts which absorbs the moisture from the prevailing atmosphere.

true. earthquakes are felt whenever there is a slip around a fault in the rocks below the earth. this reorientation of faults create sesmic waves and is known as earthquake, the severity of which is measured in richter scale. these are more prominent in hilly regions as the rocks usually form faults to balance the pressures on it.