Possible mechanisms for T-phase generation

Abstract

Recent extensions to the wave-number-integration approach [Schmidt et al., J. Acoust. Soc. Am. 98, 465–472 (1995) and H. Schmidt, J. Acoust. Soc. Am. 97, 3316(A) (1995)] have made it possible to apply spectral methods to stepwise range-dependent elastic problems. Using these methods, it is possible to study the potential mechanisms of T-phase generation in oceanic waveguides. Such a study has applications in the prediction of tsunamigenisis from T-phase observations. The general environment considered is a canonical sound-speed profile and sloping bottom. The seismoacoustic field is determined via the above spectral methods, and then a modal decomposition is applied. The initial modal excitation and subsequent energy exchange from coupling is examined. The energy that becomes trapped in the water column is indicative of what might be observed on a distant hydrophone. The inclusion of elastic effects in these range-dependent scenarios is likely to be critical in order to fully model the T-phase generation. For a sloping elastic bottom, the lower modes may actually be directly excited by the shear waves, whereas energy injected from compressional waves in the bottom must couple down through the higher modes. The strong presence of low-order modes is consistent with observations. This study considers the importance of a variety of parameters, including slope, source-depth, frequency and bottom characteristics. Both rift and slope bathymetries are considered. [Work supported by ONR.]