Issues with Signal Decay in Specfem2D and Clarification on Material Property Settings

[liaohaiyang1534]

Issue 1: Signal doesn't decay after a specific trace

I am currently using specfem2d for numerical simulation of forward geophysical data. Within my simulation, I set up a point force source. I anticipate the signal to decay along the trace and over time. However, in the simulation results, I observed:

At the beginning, the signal does decay as expected;
But, when it reaches around the 20th trace, the decay ceases, and its intensity remains consistent;
There are a total of 60 traces in my simulation.
I've considered and tried the following to diagnose the issue:

Suspected issues with material property settings but didn't get the expected outcome after modifications;
Pondered if the issue could be related to the source setup;
Thought it might be due to numerical dispersion, but the issue persisted even after reducing the time step.
I'm quite puzzled about this and would appreciate any advice or guidance.

Issue 2: Question about material property settings in specfem2d

I have generated several model files for specfem2d using cubit(python) and attempted to integrate CPML absorbing boundaries. However, I noticed that the nummaterial_velocity_file isn't being utilized, and the material properties seem to be controlled by the settings within the Par_file.

Here's the material property section from my Par_file:

# number of model materials
nbmodels                        = 1
...
1 1 1500.d0 1000.d0 300.d0 0 0 9999 9999 0 0 0 0 0 0
2 1 2500.d0 2700.d0 0 0 0 9999 9999 0 0 0 0 0 0
3 1 2200.d0 2500.d0 1443.375d0 0 0 9999 9999 0 0 0 0 0 0
4 1 2200.d0 2200.d0 1343.375d0 0 0 9999 9999 0 0 0 0 0 0

My question is: Should I control the material properties directly within the Par_file instead of relying on the nummaterial_velocity_file?

If anyone has any possible solutions or hypotheses about these issues, I'd greatly appreciate that.