The amplification of waves inside the ports becomes critical under extreme events (storms or tsunamis) by causing unexpected amplification and damage in the ports. The resiliency of harbors and coastal utilities against marine hazards is important for the post disaster recovery operations. Resonance oscillations and resultant wave amplifications inside the basins are other important adverse effects which cause damage on structures and interruption of harbor functions. Those are necessary for the post event recovery operations. One of the important utilities located in Istanbul coast near Marmara is the port of Haydarpasa where regular shaped basins were designed inside the harbor. The resonance oscillations, periods of free oscillations and flow pattern of long waves in Haydarpasa port under the actions of long waves are investigated using numerical model (NAMI DANCE). An initial impulse is inputted, and a simulation is performed. The time histories of water surface fluctuations are computed at several numerical gauge points inside the harbor. The spectral analysis by using Fast Fourier Transform technique is applied to the records of all numerical gauge points and respective spectrum curves are obtained. The peaks of spectrum curves of each numerical gauge location are also determined. The peaks of spectrum curves coincide with the resonance frequencies. The computed frequencies are discussed by comparing with the frequency of the waves which occur in the Marmara Sea in regard to their possible amplification and effects to Haydarpasa port.