A　physical　method　for　modeling　the　phase　spectrum　of　earthquake　ground　motion　is　derived　by　defining　relationships　between　the　envelope　delay　and　Fourier　amplitude.　In　this　method,　two　parameters　with　clear　physical　meanings,　namely　the　median　arrival　time　and　strong　shock　duration,　are　introduced.　These　parameters　provide　a　logical　basis　for　modeling　the　phase　spectrum　in　a　physical　sense.　A　simulation　method　for　earthquake　ground　motions　is　introduced,　based　on　a　physical　amplitude　model　and　the　proposed　method　for　modeling　the　phase　spectrum.　To　investigate　the　physical　meaning　of　the　phase　spectrum　of　earthquake　ground　motion　and　to　be　used　for　simulating　earthquake　ground　motions,　two　techniques　based　on　the　discrete　Fourier　transform　(DFT)　and　the　continuous　Fourier　transform　(CFT)　are　employed　to　calculate　the　envelope　delay.　It　is　demonstrated　that　when　using　the　DFT,　the　range　of　envelope　delays　is　dependent　on　the　duration　of　the　earthquake　ground　motion,　and　the　range　of　envelope　delays　corresponding　to　peak　amplitudes　is　dependent　on　the　time　span　of　the　strong　shock　in　ground　motions.　This　dependency　is　not　observed　with　the　CFT.　The　proposed　simulation　method　for　earthquake　ground　motions　was　used　to　regenerate　two　recorded　earthquake　acceleration　time　histories.　Numerical　results　demonstrate　that　this　method　can　accurately　reproduce　the　main　characteristics　of　strong　earthquake　ground　motion　recordings.