Answer: Basalt is denser than sand
Step-by-step explanation:
Seismic waves are mechanical waves (meaning, they must pass through a medium). Because basalt is denser than sand, a seismic wave will travel faster through basalt. The atoms of basalt are more tightly packed together than the atoms of sand. Collisions between atoms of basalt are more frequent because they are closer together, therefore the kinetic energy is higher. The higher the kinetic energy, the higher the velocity of the wave.