The dynamics of abyssal T-phases

Abstract

The characteristics of earthquakes, as revealed by T-phase observations, have the potential to provide important constraints on physical models of crustal processes under the oceans. Although it has been postulated that some form of scattering at or near the seafloor is necessary to convert the compressional and shear body waves from earthquakes into the low grazing angle paths necessary for propagation in the ocean sound channel, there are T-phase observations that cannot be explained by seafloor scattering alone. Water depth above the epicenter, for example, should have a strong effect on T-phase excitation. We use the time domain finite-difference method combined with ray theory to demonstrate these issues and we compare the theory to a series of events that occurred near the mid-Atlantic Ridge at the Kane Fracture Zone (MARK) in 1999 and 2000. There is evidence in this data set which suggests that topographic steering of T-phase locations occurs. Earthquake energy appears to preferentially enter the sound channel at topographic highs and epicentral locations are biased toward shallow bathymetry.