Final answer:
The wiggles on a seismogram are caused by seismic waves: P-waves, S-waves, and surface waves. P-waves arrive first and have higher speeds, followed by slower but more damaging S-waves, and then by surface waves which cause the most damage.
Step-by-step explanation:
The up-and-down wiggles on a seismogram are caused by different types of seismic waves generated by earthquakes. The primary types of waves are P-waves (longitudinal waves also known as compressional waves), S-waves (transverse waves also known as shear waves), and surface waves. P-waves are the fastest seismic waves and thus arrive first at a seismograph.
S-waves, which can only move through solids, arrive after P-waves and are slower but can cause more damage. Finally, surface waves travel along the Earth's surface and are responsible for most of the damage during an earthquake as they have larger amplitudes and longer durations.
Differentiating between these waves is crucial because they travel at different speeds and provide important information about the Earth's interior structure. P-waves typically have speeds of 4 to 7 km/s and S-waves have speeds of 2 to 5 km/s. The time difference between the arrival of P- and S-waves at a seismograph station is used to calculate the distance to the earthquake's epicenter.