How can earthquakes trigger seiches in gulfs?

Earthquakes trigger seiches—rhythmic oscillations of water—in gulfs primarily through the propagation of seismic surface waves. When these waves pass through a region, they disturb the water surface, forcing it out of equilibrium.123

Once the water is displaced, gravity acts to restore the horizontal surface, initiating a simple vertical harmonic motion. This impulse travels the length of the basin and reflects off the boundaries, creating standing waves. Because gulfs are often partially enclosed or have narrow mouths, they are particularly susceptible to these free oscillations. The resulting seiche can persist for hours or even days after the initial seismic activity has ceased, as the water continues to swing according to the dimensions of the basin.1423

In addition to direct seismic waves, earthquakes can also trigger seiches indirectly through the generation of tsunamis, which can induce similar rhythmic sloshing when they enter coastal inlets.13