What is the term for the originating earthquake source of the elastic waves inside the earth?

The term for the originating earthquake source of the elastic waves inside the Earth is the focus. The focus, also referred to as the hypocenter, is the specific location within the Earth where the seismic energy is first released during an earthquake. It is the point at which the fault begins to rupture, and it is typically located deep underground, beneath the epicenter.

Understanding the focus is crucial in seismology as it directly influences the intensity and characteristics of the seismic waves that then travel outward through the Earth's crust. This is in contrast to the epicenter, which is the point directly above the focus on the Earth's surface. While both terms are associated with earthquakes, the focus specifically describes the starting point of the seismic activity deep within the Earth.

Magnitude and intensity, on the other hand, are measures related to the energy released and the effects of the earthquake felt at the surface, rather than the originating point of seismic waves.