The discovery that there are two types of seismic waves, compression waves (P-waves) and shearing waves (S-waves), is credited to the Croatian seismologist Andrija Mohorovičić. In 1909, Mohorovičić observed distinct arrival times of seismic waves at different seismograph stations during an earthquake in Croatia. He noticed that some waves arrived before others, and based on their behavior, he classified them into two types: primary waves (P-waves) and secondary waves (S-waves). P-waves are compressional waves that travel faster and can propagate through both solid and liquid materials, while S-waves are shearing waves that travel slower and can only pass through solid materials. This discovery laid the foundation for understanding the behavior of seismic waves and the internal structure of the Earth.