I have been long looking for the derivations and step by step explanation of Zoeppritz matrix but either internet is full of final versions or I can’t find it...I would be very thankful if anyone can direct me or provide me with derivations.
A DuckDuckGo search for "Zoeppritz matrix" gives the Wikipedia entry for "Zoeppritz equations" as the second link. The Wikipedia entry says:
A full derivation of these equations can be found in most exploration geophysics text books, such as:
Sheriff, R. E., Geldart, L. P., (1995), 2nd Edition. Exploration Seismology. Cambridge University Press.