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A dam's responses can be amplified by the geometry and flexibility of its surrounding canyon. To modeling a canyon as an elastic unbounded domain, the radiation damping condition should be satisfied, and in this regard, the Scaled Boundary Finite Element Method (SBFEM) is a powerful tool. In this article, a substructure method was used to combine the standard Finite Element Method (FEM) with the SBFEM, resulting in the hybrid FEM‐SBFEM technique. This hybrid technique treats an earth dam by using FEM and a corresponding elastic unbounded canyon by SBFEM. The proposed approach was verified by data available in the literature. The seismic response of an earth dam‐flexible canyon system was investigated by employing a 3D FEM‐SBFEM method. Several amplification functions corresponding to different canyon conditions were obtained by applying a uniform displacement for the canyon boundary, and a comprehensive study was performed to examine the effects of canyon geometry and flexibility on the steady‐state response of the dam, as these two effects influenced the amplification functions. While the flexibility of the canyon significantly affects the maximum amplification function value for a dam, this value does not change for earth dams in canyons with different shapes but the same length. In addition, the lateral response of earth dams in the time domain was computed in order to analyze the aforementioned effects under an actual earthquake. The proposed amplification functions were used to compare the recorded response spectra of the El Infiernillo dam under the two earthquakes in 1966 with the calculated amplification function, and a reasonable agreement was observed between them.

The finite element method (FEM) is a powerful tool for the nonlinear modeling of dynamic problems. In the present work, the equivalent linear method (EQL) has been implemented into the FEM. For stratifying the radiation damping condition and rigorously modeling canyon as an elastic unbounded domain, the scaled boundary finite element method (SBFEM) was utilized. The FEM‐SBFEM technique, wherein FEM is coupled with SBFEM, has been extended to take into consideration the effect of earth dam material nonlinear behavior. It was observed that the nonlinear behavior greatly affects the natural frequency, the amplification function (AF), and peak crest acceleration of the earth dam located in canyons. The effects of canyon geometry and flexibility on the nonlinear behavior were examined, and it was seen that by increasing the flexibility of the canyon, the effect of nonlinearity was decreased. The El Infiernillo dam was modeled by 3D proposed technique, and a comparison of the crest AF obtained by the proposed method with the recorded data shows the accuracy of the methodology.