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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 2102 Three-dimensional share wave speed structure beneath the South Pacific superswell Dr. Takehi Isse JAMSTEC IFREE IASPEI Daisuke Suetsugu, Hajime Shiobara, Hiroko Sugioka, Kazunori Yoshizawa, Toshihiko Kanazawa, Yoshio Fukao, Guilhem Barruol We determined three-dimensional shear wave speed model beneath the South Pacific superswell down to a depth of 200 km by analyzing broadband data from ocean bottom seismograph and island stations temporary deployed in the French Polynesia region. The temporal data covers period from 2003 to 2005 for the BBOBS stations deployed on the seafloor and from 2001 to 2005 for the island stations deployed during the PLUME project. This enables us to study the upper mantle structure beneath the Superswell with an unprecedented high resolution. We measured the dispersions of fundamental mode of Rayleigh waves at periods between 40 and 140 seconds by using a two-station method. Resolution analyses indicate that these temporary stations may locally improve the lateral resolution to about 400 km. We observe superficial slow anomalies associated to the spreading ridges such as the Lau Basin and two kinds of hotspot signatures: We found pronounced and continuous slow anomalies down to at least 200 km depth near the Society, McDonald, Marquesas, and Pitcairn hotspots whereas the slow anomalies beneath the Samoa, Rarotonga and Arago hotspots are only present at depths shallower than 80 km. Keywords: surface wave tomography, bbobs, superswell

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 2103 Subduction roll-back, slab break-off and induced strain in the uppermost mantle beneath Italy Dr. Lucia Margheriti CNT INGV IASPEI Francesco Pio Lucente Differences in the splitting amount of SKS waves that traverse the upper mantle beneath the Italian region identify four areas of internally coherent delay times, providing evidences for mantle strain partitioning. If compared with the uppermost mantle structure of subduction imaged by tomography, the sequence of these areas displays a straightforward parallelism. Under certain assumptions, the highlighted correspondence between areas of coherent splitting amount and areas of coherent velocity perturbations offers new insights on the last evolution phases of subduction in Italy and on the way they affect the mantle strain. Keywords: anisotropy, mantle strain

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