Wave response Program

Upon reading the manual of Wave Response, it suggests that it calculates equivalent static load in order to solve directly (section 1.2). How is this type of analysis different from a normal static conventional analysis ? 

1) Stiffness of the structure remains same as that of a standard Stiffness Analysis (static) ?

2) DAF for the structure automatically gets involved in this equivalent static Load ?  

3) PILSUP command requires input of  Load cases to calculate pile stiffness in Global X or Y Direction. Stiffness of Pile is intrinsic and dependent upon Soil Properties & Pile Geometry. How do load cases determine the stiffness ? Should the load cases entered be the environmental condition or Dead Load ?