Final answer:
The moment magnitude scale measures earthquake strength based on the seismic waves produced, which include P-waves arriving first and S-waves arriving subsequently. These waves' speeds depend on the medium's rigidity, with P-waves being faster, especially in rigid materials like granite.
Step-by-step explanation:
The moment magnitude scale is used to measure the strength of earthquakes and does not start as surface waves, travel through liquids, or vibrate from side to side. Moreover, it does not describe waves that move slower than S-waves. Instead, the moment magnitude scale is a more accurate measurement than the older Richter scale, especially for large earthquakes, because it takes into account the area of the fault that slips, the amplitude of the seismic waves, and the rigidity of the rocks that break during the earthquake.
P-waves, also known as compressional or pressure waves, are longitudinal and arrive first at seismograph stations. They travel faster through more rigid materials, ranging in speeds from 4 to 7 km/s. S-waves, or shear waves, are transverse and travel at speeds of 2 to 5 km/s but cannot propagate through the Earth’s liquid core. They arrive after P-waves and along with surface waves, can be more damaging due to their motion at the Earth's surface. The time difference between the arrival of P-waves and S-waves at a seismograph is used to calculate the distance to the earthquake's epicenter.
The speed of seismic waves depends on the rigidity of the medium they travel through. In more rigid materials such as granite, both P-waves and S-waves travel faster in comparison to less rigid materials like sediments.