How to choose trace width for very high current PCB?
It's not the current that matters, it is heat.
The current will heat up your copper on top of the FR4.

The heat generated is current squared time resistance of (trace + solder joints + component leads).
The square in there is what makes the high currents so scary, even ath the 1:10k duty cycle you have on the positive side of the balance sheet.

So I agree with Dans answer very much: a trace suitable for a 10A continous current should do the trick.
"Suitable" menas that the heat does not increase your PCB temperature more than your specifications allow for.
Which as usul depends on many factors like type of PCB, overall heat sources on it, hos the heat is dissipated to the environment etc.

hase