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 Poster presentation 2175
D" structure investigated using source array migration
Mr. Jeremy Chaloner
Department of Earth and Ocean Sciences University of Liverpool IASPEI
Christine Thomas, Andreas Rietbrock
TheD"region of the lowermost mantle has been much studied in recent years. Better understanding of
its structure will shed light on mantle convection systems and core-mantle interactions. Most studies of
the lowermost mantle utilise reflected waves off the top of the D" discontinuity. This discontinuity is
found in many locations, but especially where tomographic models indicate higher than average seismic
velocities. Extending studies into areas of slower seismic velocities will be significant, since coverage of
such areas is sparse at present.We investigate D" structure under the western Pacific, north-west of the
Marshall Islands, by using earthquakes in the Philippines to construct a source array. Using recordings
of up to 300 earthquakes in the Philippine Sea recorded at KIP in Hawaii, we stack records of
earthquakes with suitably similar source mechanisms to perform a migration. This is used to attempt to
detect reflectors in D" for both P and S-waves. This region is shown in tomographic studies to be
seismically slow near the core-mantle boundary. This means that the presence and nature of a D"
velocity discontinuity will have strong implications for the role of post-perovskite in creating this
discontinuity. In addition the double crossing model (perovskite to post-perovskite and back to
perovskite) can be tested.
Keywords: d double prime, mantle, core mantle boundary