What are some differences between P- and S-waves?

• Which arrives first at the observer and why?
• If the observer were standing closer
• WHy do most earthquakes occur close to the Earth's surface, relative to the entire depth of the Earth?/li>

Key points

• P-waves arrive sooner than S-waves because P-waves move faster.
• Earthquake waves radiate out in all directions through the Earth.
• Both P-waves and S-waves start out from the focus at the same time.
• First arrivals of the P-wave and S-wave on the seismogram mark the arrival of the outermost edge of each radiating sphers of disturbance shown on this diagram.
• After the first arrivals, the seimogram is recording the complex net disturbance due to multiple coincident waves.
• We ignore surface waves here, but surface waves and other conplexities make many actual seismograms too complex to discuss here.