I have generated a synthetic seismogram using FDTD elastic velocity-stress formulation on a staggered grid. I can't understand origin of oscillations modulating on seismogram.
Is it a result of dispersion?
I have satisfied the grid dispersion criteria (10 grid per minimum wavelength) which keeps it below 5% but still it is very prominent.
Velocities: Vp = 2000 m/s; Vs = 1500 m/s;
Source: Ricker (20Hz).
Grid spacing: dx = dv = 1m;
time sampling: dt = 0.1msec
I have corrected one problem related to source (now I am using soft source) and it made initial pulse smooth. However its tail still have oscillations.