The Equivalent Lateral force method is a static method where the base shear and the corresponding distribution of the pseudo-static force is based on only the Fundamental mode. Whereas, in the Response Spectrum analysis, program solves the Eigen Solution to determine the other mode shapes and the corresponding natural frequencies. Now, the responses like displacement or the forces are determined by the combination of the maximum responses against every individual modes. For example, considering that SRSS combination is invoked, the final response is determined by the Square root of the summation of the squares of maximum responses against individual modes and hence the total base shear in this case is expected to be higher that that of the Static case.
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