Correct Option
The correct option is 2 only.
Explanation
Tsunamis (Japanese for "Harbour Wave") are a series of large ocean waves caused by the sudden displacement of a large volume of water. While they are most commonly generated by undersea earthquakes, they can also result from volcanic eruptions, landslides, or meteorite impacts.
Statement-wise Analysis
- Statement 1 is Incorrect: Tsunamis are not earthquakes themselves; they are the secondary effect (waves) generated by the displacement of water. An earthquake is the release of seismic energy causing ground shaking, whereas a tsunami is the propagation of water waves resulting from that event. Furthermore, tsunamis are aquatic phenomena, though they strike land; describing them as "earthquakes that occur on land" is conceptually wrong.
- Statement 2 is Correct: For an earthquake to generate a tsunami, there must be a vertical displacement of the water column. This typically occurs when the epicentre (or more accurately, the fault rupture) is located below the ocean floor. The vertical movement of the seabed pushes the water up or down, initiating the wave. Earthquakes with epicentres deep inland generally do not displace oceanic water to cause tsunamis.
- Statement 3 is Incorrect: A magnitude of 5 on the Richter scale is generally considered moderate and is insufficient to generate a devastating tsunami. Tsunamigenic earthquakes-those capable of generating destructive tsunamis-typically have a magnitude of 7.0 or higher. Earthquakes of magnitude 5 may be felt but rarely cause the massive vertical seabed displacement required to generate a devastating tsunami.
Key Takeaway
Tsunamis are generated by the vertical displacement of the ocean floor during large undersea earthquakes (usually magnitude 7.0+). They are distinct from the earthquake itself and require the disturbance to occur beneath the water column.