Problems with external source files and output result files

[KL-47]

Dear seniors,

I wish the families of all seniors healthy. SPECFEM2D is a very meaningful software and I have been installing, running, and learning it for over a year now. Since I am a graduate student in civil engineering, I still have some questions that I don't understand after all this time. I would be appreciated your guidance.
Question 1: In the external source file, when using the option time_function_type = 8, the external input source is a file containing time and amplitude, does amplitude here refer to displacement (unit: m)? However, the options of source_type are only force (unit: N) and moment tensor (unit: N‧m), which seems contradictory. Moreover, in the paper "Introduction to the spectral element method for three-dimensional seismic wave propagation" and in the question "Reciprocity test for visco-mechanical wave propagation #1081", I see that the external source used by the predecessors is also force (unit: N). So, what should this amplitude refer to? Is it possible to use displacement time history as an external source?
Question 2: In the file name of the simulation result in Specfem2D soft (e.g. AA.S0001.BXX.sem*), do BXX and BXZ refer to both X and Z directions or XX and XZ directions? If it is XX and XZ directions, how should I understand these two directions? Do they have any connection with P-wave, SV-wave, and SH-wave directions?

Yours sincerely,
Zheng Wang