Abstract: Isolating source spectra is all important step toward for better understanding earthquake source radiation where the nucleation processes is a complex but essential area in modem seismology．To study the spectrumof ground motion radiated from the earthquake source，we must first remove the path and site effects from observed ground motions．Attenuation effects include geometric spreading，anelastic attenuation，and near-surface attenuation．There are also crustal amplification effects，which can be significant where there exists a strong velocity contrast or gradient．Comparing the earthquake source radiation from six tectonic regions: California， Mexico，Turkey，Japan，eastern North America(ENA)and British Columbia(B．C．，Canada)，I found that source spectra are approximately independent of region，distance，and depth when path and site effects are properly removed．Kappa values vary regionally．The lowest kappa value corresponds to the hard rock sites in a stable intraplate environment(ENA)while generally higher kappa values correspond to the site conditions in active tectonic environments such as Japan，Mexico，B．C．，California，and Turkey．