  The complex critical points are analyzed in the 4-dimensional Lorentzian
Engle-Pereira-Rovelli-Livine (EPRL) spinfoam model in the large-$j$ regime. For
the 4-simplex amplitude, taking into account the complex critical point
generalizes the large-$j$ asymptotics to the situation with non-Regge boundary
data and relates to the twisted geometry. For generic simplicial complexes, we
present a general procedure to derive the effective theory of Regge geometries
from the spinfoam amplitude in the large-$j$ regime by using the complex
critical points. The effective theory is analyzed in detail for the spinfoam
amplitude on the double-$\Delta_3$ simplicial complex. We numerically compute
the effective action and the solution of the effective equation of motion on
the double-$\Delta_3$ complex. The effective theory reproduces the classical
Regge gravity when the Barbero-Immirzi parameter $\gamma$ is small.
