How earthquake waves radiate outward from an epicenter
Observe & Discuss:
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>
- 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.