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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. enter image description here

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.

Model description: Velocities: Vp = 2000 m/s; Vs = 1500 m/s; Source: Ricker (20Hz). Grid spacing: dx = dv = 1m; time sampling: dt = 0.1msec

Edit 1

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. Pressure corrected

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    $\begingroup$ 0.1 ms seems like a very short interval, given the other parameters. Does it help at all if you use 1 ms? Make sure you are handling units properly (I find it best to do everything in seconds). $\endgroup$ – kwinkunks Apr 14 '16 at 23:06
  • $\begingroup$ @kwinkunks I took care of units in first run itself. I carried out experiment with various values of 'dt' but all these oscillations increase with increase in time. I am using a Ricker wavelet of 30Hz frequency. Any suggestions about origin or cause of these oscillations. $\endgroup$ – Amartya Apr 15 '16 at 17:25
  • $\begingroup$ Do you have any sharp edges that introduce oscillations after transformation? $\endgroup$ – Way of the Geophysicist Apr 21 '16 at 15:20
  • $\begingroup$ @WayoftheGeophysicist I have taken a homogeneous model so it doesn't have any discontinuity. Additionally, all the edges have absorbing boundary layers so they won't be producing any reflections. $\endgroup$ – Amartya Apr 22 '16 at 16:39
  • $\begingroup$ Have you considered taking a FFT of your data and identifying the wavelengths corresponding to the oscillation? $\endgroup$ – BarocliniCplusplus Apr 26 '16 at 1:04

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