Check that you are using the correct hazard factors, damping and site subsoil class for the response spectrum by going to; Define/Functions/Response Spectrum/Modify. The check that you are mobilizing sufficient modes with your frequency analysis also (Min 20 modes for Eigen, about 10-15 for Ritz, min 90% mass participation for both)
Otherwise, check your units for the scaling factors for the Response Spectrum load case.
Also worth checking that the "comparison" case of Seismic loads (Auto lateral loads) is including the appropriate masses and live loads, and is assuming the same parameters as your response spectrum.
Ultimately you should get very similar results between the two analyses. The main benefit of the response spectrum is that it is independent of load direction and gives you a single "envelope" design case.
Finally, do a hand check to the code in addition to the above. ETABS can be the epitome of black-box technology if you are not careful with your checking.
Did some hand checks this morning. Results look fine.I chose a bigger Time period for Equivalent Force Method which gave me low base shear. But still base shear from response spectrum is bigger than that obtained from ESA. That's why I was surprised at first because in all my previous projects response spectrum base shear came out to be lower. Since my hand calcs agree with this values I will take that.
Check that you are not double counting the dead load case in the mass source. If you are specifying the mass as by self weight and loadcases, and have specified the dead load with self weight factor of 1 you will be double counting the load.
Check the 1st mode period using Rayleigh or similar method.
