A finite-difference modeling plus slowness analysis method is developed to investigate near-source explosion energy partitioning and Lg-wave excitation. The finite-difference method is used to calculate seismic wave excitation and propagation, and an embedded array slowness analysis is used for quantifying how energy will be partitioned into the long-range propagation regime. Because of its high efficiency, the method can simulate near-source processes using very fine structures. A large number of source and model parameters can be examined for broad-frequency ranges. As examples, P-pS-to-Lg and S*-to-Lg conversions in the presence of near-source scattering are tested as mechanisms for Lg-wave excitation. The numerical results reveal that the depth of the source and the depth of the scattering process have strong effects on P-to-S conversion and partitioning of energy into trapped or leaking signals. The Lg-wave excitation spectra from these mechanisms are also investigated. The modeling shows that S*-to-Lg excitation is generally stronger for low frequencies and shallow source depths whereas P-pS-to-Lg scattering is stronger for high frequencies.