Understanding building dynamics is essential for accurate seismic performance assessment, especially when using nonlinear static procedures like pushover analysis. This study examines a seven-story reinforced concrete residential building in Mexico City, aiming to determine its vibration periods and modal shapes through ambient vibration testing. The goal is to define a realistic lateral load distribution for subsequent nonlinear analysis based on the structure’s dynamic properties. Ambient vibration signals were recorded with servo-accelerometers at various levels. These asynchronous signals were processed using the Complex Mode Indicator Function (CMIF), while Nakamura’s method was used to exclude the dominant soil period. Independent Component Analysis (ICA) was then applied to extract statistically independent modal components. The study identified vibration periods and torsional modes in both orthogonal directions. Modal shapes were derived from transfer functions and phase angles. Results show that ICA is a reliable alternative to traditional spectral methods, especially for irregular or complex structures. The key finding is that ICA provides a more accurate, structure-specific load pattern, enhancing the reliability of pushover analysis.