torsional vibration

In seismology, torsional vibrations, designated as T modes, are a type of seismic wave where the Earth's elements experience shear but no radial displacement. These vibrations, along with spheroidal vibrations (S modes), are set up by the energy release from an earthquake and can continue for hours or even days. Modern digital seismographs can record a wide spectrum of these ground movements, from short-period P waves to very long-period oscillations. The study of these free vibrations provides crucial information about the Earth's interior structure by analyzing their periods and decay rates, measured by a quality factor Q.1