Which of the following is /are direct source(s) of information about the interior of the earth? 1. Earthquake wave 2. Volcano 3. Gravitational force 4. Earth magnetism Select the correct answer using the code given below.

Information about the Earth's interior is categorized into direct and indirect sources. Direct sources involve physical materials or phenomena that originate from the interior and reach the surface, such as volcanic eruptions, which bring magma and rocks from deep zones like the mantle. Mining and deep-sea drilling are also direct sources. Conversely, indirect sources rely on the analysis of physical properties and mathematical models. Earthquake (seismic) waves are considered indirect sources because scientists deduce the interior's structure by analyzing changes in wave velocity, reflection, and refraction patterns [1]. Similarly, gravitational force (gravity anomalies) and Earth's magnetism (magnetic surveys) are indirect sources as they provide data on density distribution and magnetic material concentration without providing physical samples from the deep interior. Therefore, only volcanoes among the listed options are direct sources.

Sources

1. [1] Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 4: Earths Interior > Seismic Waves > p. 58