Consider the following statements:

Answer: (c) Both 1 and 2

Speed (P first) and motion (push–pull vs side-to-side) — the two basic ways the waves differ.

Statement by statement

1. ✓ CORRECT P (primary) waves are the fastest seismic waves, so they reach the seismograph first; S (secondary) waves come next.

2. ✓ CORRECT P waves are longitudinal (push–pull, like sound). S waves are transverse (up–down, at right angles to travel).

The idea

Separate the speed of a travelling disturbance from the direction in which particles move. A compression wave pushes particles along its path; a shear wave moves them across its path. Compression travels faster than shear in the same solid material.

Fault slips → Compression and shear disturbances begin → P waves travel faster through the rock → P waves reach the station first → Slower S waves arrive later → Arrival-time gap helps estimate distance

Why the others are wrong

(a) Doubts statement 2 because of its length. It is simply longitudinal (P) vs transverse (S) motion.

(b) Doubts statement 1. P waves are the fastest, which is why they are called “primary” — they arrive first.

(d) Would mean S waves arrive first, which contradicts their name and speed.

The trap

Long, technical statement 2 makes people doubt it. It is just longitudinal vs transverse, word for word from NCERT.

Also know

The focus is the underground origin of a quake; the epicentre lies directly above it. S waves cannot pass through the liquid outer core, whereas P waves are bent as they enter it. Surface waves travel along the surface and often cause severe damage. Seismographs at several stations help locate an earthquake.