The observation of inner core shear waves

Abstract

Although the Earth's inner core has long been thought to be solid, there have not, as yet, been unequivocal observations of inner core shear waves. Here we present observations of the phases pPKJKP and SKJKP for the Flores Sea event of 1996 June 17. The observations support the value of approximately 3.6 km s-1 for the inner core shear wave velocity and open up new possibilities for exploring the anisotropic structure and the attenuation properties of the inner core. The analysis and validation of the observation is based on a new method that can be used in the search for and identification of inner core shear waves. In this method normal mode synthetics for a solid inner core are compared with those for a fluid inner core. It is only by such comparisons that it is possible to be certain that inner core shear waves, rather than interferences of other phases, are responsible for observed energy maxima in stacked seismic records.