IASPEI - Picture Gallery

IUGG XXIV General Assembly July 2-13, 2007 Perugia, Italy
(S) - IASPEI - International Association of Seismology and Physics of the Earth's
Interior
JSS011 Oral Presentation 2130
Regional Scale Variation of the top Layer of the Inner Core Beneath Pacific
Prof. Shingo Watada
Earthquake Research Institute University of Tokyo IASPEI
Differential traveltime of seismic core phases has been used to probe the surface layer of the inner core,
although, the differential traveltime data show large scatter relative toa reference earth model. The
origin of the scatter has been speculated, for example,sharp seismic velocity boundaries in the top of
the mantle and strong heterogeneity above the CMB, or in the inner core. The large aperture dense
seismic array, Hi-net, is suitable for the study of the regional scale variation of core phases because its
short station spacing enables us to measure the traveltime of short-period body waves from waveforms
without spacial aliasing. The pattern PKPcd-df and PKPbc-df differential traveltime from deep focus
earthquakes in South America shows a clear systematic gradient within the Japanese islands. For
example 0.5 s difference occurs over a 300 km distance for PKPbc-df, suggesting a short scale variation
of P-wave velocity of the top 300 km of the inner core. The core phases propagate the inner corein the
east-west directionbeneath Pacific where strong anisotropy is not expected. Rich short-scale
heterogeneity in addition to the well documented hemispheric structure in the inner core may hide in
the scatter of the differential traveltime of core phases over the globe. The scale and size of the
regional structural variation of the innerrevealed by a large-aperture dense seismic array will provide
obsevationalconstraint forthe style of convection of the inner core.
Keywords: traveltime, seismic core phases, inner core