Thanks Sureshprsharma for your reply, however you are not entirely correct. If you increase the load in loadcase 20 in Z direction say by factor of 5, 10 or 100, then you start seeing reaction at node 1. Then the statement that " There is no scope for the structure to vibrate in Z direction because of the fixed support at node no. 1. Hence there is no reaction due to seismic load in Z direction."
Somehow the effect of load in Z is much lower and with the load use it give 0 reaction, which does not seems correct. If you remove the load and just look at selfwight in the response spectrum loadcase, you still get a reaction in Z due to slefweight which is higher than when you add in the loads.