Earthquake Waves (Seismic Waves)

Definition

The vibrations released from the focus of an earthquake that travel through and around the Earth; their study reveals both ground shaking and the layered structure of the Earth's interior.

Key points

• Body waves travel through the interior: P-waves (primary, longitudinal or push-pull, the fastest, arrive first) and S-waves (secondary, transverse, slower).
• P-waves pass through solids, liquids, and gases; S-waves pass only through solids, which is the key evidence that the outer core is liquid.
• Surface waves (such as Love and Rayleigh waves) travel along the surface, are slowest, and cause most of the destruction.
• The point of origin underground is the focus (hypocentre); the point directly above on the surface is the epicentre.
• Magnitude is measured on the Richter scale (energy released) and shaking effects on the Modified Mercalli scale (intensity); the S-wave shadow zone proves the molten outer core.

Why it matters for CAPF

The P versus S distinction, the S-wave shadow zone proving a liquid outer core, and the focus versus epicentre pair are classic objective items, and earthquakes link to disaster management and NDRF deployment.

Common confusion

P-waves (primary, longitudinal, fastest, through solid and liquid) versus S-waves (secondary, transverse, slower, solids only); focus (underground origin) versus epicentre (point above on the surface); Richter (magnitude) versus Mercalli (intensity).

Parent note

geomorphology earth interior and plate tectonics