How do you calculate short circuit current for buses on a single line diagram?

check total fault impedance then divide it to voltage at fault point u will get desired current value.

by using The MVA method is a modification of the Ohmic method where the impedance of a circuit equals the sum of the impedance of components constituting the circuit.
Using the admittances, it follows that the reciprocal of the system impedance is the sum of the reciprocals of the admittances of the components.