Tomographie des temps d'arrivée au-delà de la théorie des rayons

• Main Author: Montelli, Raffaella
• Other Authors: ExxonMobil Upstream Research Company, ExxonMobil, Université Nice Sophia Antipolis - Faculté des Sciences (UNS UFR Sciences), Université Nice Sophia Antipolis (1965 - 2019) (UNS), Université Nice Sophia Antipolis, Guust Nolet
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: HAL CCSD 2003
• Subjects: ondes P et PP; tomographie sismique; manteau; [SDU.STU.GP]Sciences of the Universe [physics]/Earth Sciences/Geophysics [physics.geo-ph]; [PHYS.PHYS.PHYS-GEO-PH]Physics [physics]/Physics [physics]/Geophysics [physics.geo-ph]; [SDE.MCG]Environmental Sciences/Global Changes; Mid-Atlantic Ridge; Scripps; Iceland
• Online Access: https://theses.hal.science/tel-00653725; https://theses.hal.science/tel-00653725/document; https://theses.hal.science/tel-00653725/file/These-Montelli-2003.pdf

seismic tomography; p and PP waves; mantle Diffraction theory predicts that traveltimes of seismic waves with a finite dominant frequency are affected by heterogeneities within a narrow region around the ray-theoretical path, called Fresnel zone. Because of wavefront healing, heterogeneities whose scale-Iength is smaller than the size of the Fresnel zone have a reduced effect on the traveltime of a wave. Dahlen et al. (2000) show how is possible to correct for effects of wavefront healing using a new method, referred to as finite-frequency modeling. In this thesis, we investigate the effects of using finite-frequeney modeling in global seismic tomography. To reduce the consequence of the heterogeneous ray path coverage of the earth we also introduce an irregular model parameterization. To establish the influence of diffraction phenomena on the fin al tomographic image, we use a high quality long-period data set obtained from P of Masters (Scripps), that we invert both with standard ray theory and by using finite frequency modeling. The comparison of the two tomographie images shows that the velocity anomalies arc underestimated by 30 - 60% when interpreted with classical ray theory. In order to enhance the resolution of the tomographic image even further, we combine the long period arrivaI times, with the very best high-frequency measurements contained in Prof Engdahl's NEIC data set. A comparison of both data sets, as weil as the results from separate inversions, show a high level of compatibility. Ali the models show a strong correlation between low velocity anomalies and the location of a large number of known hotspots. The reliability of these anomalies was confirmed by extensive resolution analysis. As a result, we can confidently say that deep mantle plumes arc located beneath Ascension, Azores, Canary, Easter, Hawaii, Samoa and Tahiti. Many others, among which is Iceland, are of more shallow origin. Newly discovered plume-like features are clearly visible beneath the Mid-Atlantic Ridge, the South-cast ...