The “spikegram” in the middle of the slide shows the reflection coefficients at the interfaces between rock types.
If we could input and output “spikes” the seismogram would look just like the reflection coefficient series…..great!!
However due to the filtering effect of the Earth the seismic pulse is band limited* and we get our seismogram. Resolution is reduced using our seismic pulse.
*Bandwidth etc. A spike has infinite band width, that is it contains an infinite range of frequencies. The Earth absorbs high frequencies preferentially which causes the seismic wavelet to broaden. What we see is a band limited (usually approx 10-60Hz) wavelet representing the interfaces between rocks.