Estimation of Strong Ground Motion from the Great 1964 Mw 9.2 Prince William Sound, Alaska, Earthquake

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We are generating physically plausible near-field synthetic ground motions for the great 1964 Prince William Sound, Alaska, earthquake compatible with available seismological data, tectonic information, and eyewitness accounts. The first objective of this study is the simulation of the low-frequency (i.e., f <0.03 Hz) strong ground motions on selected locations and on a dense grid of observation points extending over the shallow dipping causative fault of the 1964 Alaska earthquake. In order to accomplish this task, we are utilizing the slip model proposed by Johnson et al. (1996) based on a joint inversion of tsunami waveforms and geodetic data. The calculations are carried out using the discrete wavenumber representation method (Bouchon and Aki, 1977; Bouchon, 1979) and the generalized transmission and reflection coefficient technique (Luco and Apsel, 1983). The second objective of this study is the reconstruction of the strong ground motion time histories and response spectra that the city of Anchorage experienced during the 1964 Alaska earthquake. The low-frequency (i.e., f <0.03 Hz) ground motions are generated using the methodology described previously. The intermediate-frequency (i.e., 0.03< f <0.50 Hz) ground motions are simulated by convolving Green’s functions generated by the discrete wavenumber representation method with far-field radiation pulses of circular cracks (Sato and Hirasawa, 1973; Dong and Papageorgiou, 2002a). The high-frequency (i.e., 0.5< f <8.0 Hz) ground motions are simulated using the stochastic modeling approach. The three independently derived ground-motion components are then properly combined to generate synthetic broadband ground-motion time histories and response spectra for the city of Anchorage due to the 1964 Prince William Sound earthquake. The third objective of this study is the validation of the synthetic strong ground motions for the 1964 Alaska earthquake against observed tectonic deformation, ground-motion estimates inferred from descriptions of structural damage, and eyewitness accounts. In summary, the analysis presented in this study contributes to a better understanding of the seismological aspects of the 1964 Alaska earthquake and provides synthetic time histories and response spectra for engineering applications compatible with all available information (i.e., seismological, tectonic, and eyewitness accounts). It should be noted however that the generated strong ground motions are not necessarily unique, nor do they reflect the entire uncertainty that characterizes the problem under investigation.