Huaca de la Luna is a monumental earthen complex located near Trujillo in the North coast of Peru built from 200 AD to 850 AD by the Moche civilization on the slopes of the Cerro Blanco mountain. The principal structure is a massive stepped pyramid built with millions of adobe bricks. The pyramid presents severe structural damage near the NW corner. The static and dynamic response of the pyramid is analyzed using 2D plane strain nonlinear FE models representing the east-west middle section together with the underlying soil profiles. We perform a sensitivity analysis of the static and dynamic response to (a) the pyramid stepped west side profile, (b) the underlying soil and bedrock configuration, and (c) the adobe material tensile strength. Under static conditions the models develop internal fractures but in none of the cases considered these grow to cause the structural collapse of the west side. The west side suffers complete collapse under horizontal accelerations as low as 0.135g.