Which one of the following is the other term used for 'Focus' in relation with an earthake?

In seismology, the 'focus' of an earthquake refers to the specific point within the Earth's interior where the sudden release of energy occurs and seismic waves originate [2]. This point is also technically known as the hypocentre [2]. While the focus (hypocentre) is located at depth within the crust or mantle, the point on the Earth's surface directly above it is called the epicentre [2]. Most earthquakes have a shallow focus, typically occurring at depths less than 60 km, though deep-focus earthquakes can occur much further down in subduction zones [2]. The term 'isocentre' is not a standard seismic term for focus, though 'isoseismic lines' refer to lines connecting points of equal intensity [1]. Therefore, 'hypocentre' is the correct alternative term for the focus of an earthquake.

Sources

1. [1] Physical Geography by PMF IAS, Manjunath Thamminidi, PMF IAS (1st ed.) > Chapter 14: Earthquakes > Focus and Epicentre > p. 177
2. [2] Geography of India ,Majid Husain, (McGrawHill 9th ed.) > Chapter 17: Contemporary Issues > Earthquakes > p. 8