Beginner: plotting focal mechanism

Dear gmt users,

I would like to map multiple focal mechanisms with gmt.
When I use just the example in the site, I can draw a focal mechanism with additional codes:

gmt begin focal png

gmt psmeca -R239/240/34/35.2 -Jm4c -Sc0.4 -h1 << END >
lon lat depth str dip slip st dip slip mant exp plon plat
239.384 34.556 12. 180 18 -88 0 72 -90 5.5 0 0 0

gmt end show


I have a couple of questions In this example.

1.Why do I have to type dip and slip twice (72 and -90) in the example?
If I do not know the second dip and slip, how do I make the focal mechanism?
When I just put zeros in the second dip and slip, it shows different figure.

2.What do these slip, st, exp, plon, and plat mean in the example?
The Slip means Rake?
I know the ''Rake" of each earthquake. Where do I have to enter?
Could you give me some references?

Thank you for reading this post

Think you need to read the -S documentation and select the data format you have. If your data is not in any of the five standard formats then you will need to do some reformatting yourself.

Yes, you’re right. I will try more. Thank you for your reply.