Pn and Lg spectra for Lop Nor explosions and nearby earthquakes were analyzed for source and propagation effects using a modified inversion method of Xie <1993>. Spectral analyses were performed on waveform data from Incorporated Research Institution for Seismology, Chinese Digital Seismic Network, Kazakhstan, and Krgyzstan networks. Pn amplitude variations of a factor of 20 are observed across the small-aperture (< 200 km) Kyrgyzstan network, and are probably related to three-dimensional Moho structure close to the network. Comparisons of Pn amplitudes and spectral ratios provide evidence for nonisotropic radiation pattern effects in the case of earthquakes and overshoot in explosion time histories. Complex source effects are born out in our inversion results: (1) logarithm of seismic moment (M0) from Pn and Lg spectra scale linearly with body wave magnitude (mb) for explosions (5.0≤mb≤6.0) and for earthquakes (4.0≤mb≤5.5); (2) Pn M0 estimates are similar to Lg M0 for earthquakes but are higher than Lg M0 for explosions; (3) corner frequency fc scale as quarter root of M0 for explosions and cube root for earthquakes; (4) at the same M0 level, Pn fc are 4--5 times higher than Lg fc for earthquakes and explosions; and (5) Pn source spectra are characterized by significant overshoot for explosions. Our results suggest that the cause of maximum separation between earthquake and explosion populations on plots of P/Lg spectral ratios, which typically occurs for frequencies above explosion Pn fc (between 2 and 4 Hz for explosions in this study), may be related to overshoot in the reduced velocity potential. ¿ 1999 American Geophysical Union