The type of waves measured on a seismograph during an earthquake are seismic waves, which are classified primarily into two categories: body waves and surface waves. Body waves are further divided into Primary waves (P-waves) and Secondary waves (S-waves). P-waves are compressional waves that travel the fastest and can move through solids and liquids. S-waves, however, are shear waves that can only travel through solids, making them slower than P-waves. Surface waves travel along the Earth's exterior and typically cause the most damage during an earthquake due to their amplitude and longer duration.