An Introduction to Surface Wave Analysis Michael E. Pasyanos - IRIS

Sensitivity kernels
Sensitivity kernels show the relationship between dispersion velocities and
earth structure.
They are calculated by taking the partial
derivative of the dispersion velocities
with respect to other parameters,
such as shear-wave velocity. For
instance, δU/δβ is often shown here.
With increasing period, surface waves
become sensitive to deeper velocity
structures.
They are themselves dependent on the
velocity structure, so it is non-linear.
We will be using them later when we
invert our dispersion curves for
layered velocity structure.