This paper is also a good place to start and includes a program implementation:
Feigl, K. L., and E. Dupré (1999), RNGCHN: a program to calculate displacement components from dislocations in an elastic half-space with applications for modeling geodetic measurements of crustal deformation, Computers and Geosciences , 25 (6), 695-704, doi:10.1016/S0098-3004(99)00003-5.
@EJFielding Thank you in advance for your suggestion. I will download them and read as soon as possible. I know that you are very busy 
but I really appreciate if you let me ask here my questions if I have some misunderstanding after reading them.
Sorry for my request
Dear all,
I calculated the amplitude image of two S1 images, which are used to generate that interferogram. I added them to related products as you can see in the following. Whenever I do the coregistration using S-1 TOPS Coregistration option, It ignore the amplitude as a output while I also need to coregister and match the amplitude of two images.
Could anybody please guide me about which option I can use to do it using SNAP?
I’m not sure why you need the amplitude but in my case, the coregistration produces the intensity of each image.
The intensity is nothing but the amplitude at the power of 2. Just take the square root of it to get the amplitude. If you plan to use it eslewhere of SNAP, don’t forget to convert the band (so that it is not a band created on-the-fly) and save the product.
@qglaude Thank you so much. I need to have an amplitude to do the following analysis based on the suggested references by Prof. Fielding.
Yes, I know. I generated the amplitude using Intensity and band math in SNAP, after applying TOPSAR-Split and Apply-Orbit-File for both two images. I need to coregister or match two amplitude products in any way to do that analysis.
@ABraun I don’t know. I am reading this reference now.
Michel, R., J.-P. Avouac, and J. Taboury (1999), Measuring ground displacements from SAR amplitude images: Application to the Landers earthquake, Geophys. Res. Lett., 26, 875 – 878.
Whenever I get the result and knowledge about this topic, I will share here with you. I found this paper and that technique interesting 
I think it is quite similar to the method of the Offset Trackign Tool. There is also a tutorial on it:
I would give it a try. http://step.esa.int/docs/tutorials/S1TBX%20Offset%20Tracking%20Tutorial.pdf
The tool takes GRD products.
@ABraun Yes, I agree with you based on this sentence from that paper:
Thank you so much for the tutorial. Does it only use the GRD products? Is it not possible with SLC images?
As far as I tested it the tool takes only GRD. But the coregistration is able to make good use of the resolution.
@ABraun Thank you so much. I will try all ways and share the results here. As the last question, this tool is only for S1 satellite or we can use for others like Envisat?
It works with all SAR satellites supported by SNAP.
It is possible to make SNAP use your SLC images but the module is designed for GRD in input. Personal tests (Offset Tracking : SLC vs GRDH products) makes me very skeptical about using SLC images in SNAP.
Just for info : The way the module is implemented in SNAP will not allow you to detect very fine displacements. Pixel Offset in SNAP is good for glacier displacement, for sure, but I can’t guaranty it will work for earthquake
I read the tutorial for Offset Tracking using GRDH product of S1 and also, saw the video of RUS service about Glacier Velocity With Sentinel-1. In RUS video, the scientist chose HH polarization for calibration and thermal noise removal steps but my downloaded S1 images have only VV and VH polarizations. So, I am worried about this dataset is suitable to process in this way or not?! 
What is your idea?
It does not really matter if your polarisation over land is VV for HH, but HH is definitely better for glaciers. It will be interesting to see if offset tracking works for (huge) earthquake displacements.
I will try to do this process for three earthquakes and update the results here. I hope to get the reasonable outputs for this step again.
I would say it’s unlikely to work but perhaps you get lucky. I would start with some huge earthquake with multi-metre slip on the surface.
So, if I am failed in using Offset Tracking tool in SNAP, I should make a code to find offsets tracking using S1 SLC images.
The result strongly differs with the settings, maybe you need to increase the window size.