Question

Give geographical reason.

Buildings collapsed at the foothills of the Himalayas because of an earthquake. Before collapsing they were moving forward and backward.

Answer 1

• The seismic waves can be divided into primary, secondary and surface waves.
• When energy is released from the Earth's interior, the primary waves are the first to reach the surface.
• Subjected to a ‘P’ wave, particles in the rock move in the direction of waves to and from and therefore, these waves are also called forward-backward waves. 
• Thus, during an earthquake, the buildings at the foothills of the Himalayas moved forward and backwards as they were first subjected to “P” waves.
• These movements create tremendous tension in the earth’s crust, and when the tension goes beyond limits, the energy is released in the form of waves, which is the cause of the trembling of the earth’s surface.