Question

Why is the upper mantle called the asthenosphere? 

Answer 1

1. Mantle lies below the crust.
2. The upper portion of the mantle is called as asthenosphere, The word “astheno” is a Greek word meaning 'weak'.
3. It is in liquid state and it is from this weaker zone that the molten rock materials i.e., 'magma’ find their way to the surface during volcanic eruptions. 
4. Epicenters of deep seated earthquakes are also found here. Therefore, the upper mantle is called the 'asthenosphere’.