Imaging of structure at and near the core mantle boundary using a generalized radon transform

In this thesis, concepts from inverse scattering and modem statistics are combined into a powerful tool for imaging interfaces in Earth's deep interior. Specially, a generalized Radon transform (GRT) approach is developed to image heterogeneity at and near interfaces in Earth's lowermost mantle with broadband, three-component seismograms from Global Seismograph Networks (GSN). With this GRT method I transformed ~100,000 transverse-component ScS waveforms into image gathers of a core mantle boundary (CMB) patch beneath Central America and juxtaposition of stacks of these gathers produces a 2-D image profile. To enhance this image profile, I collaborated with statisticians and used mixed-effects statistical modeling to produce the best estimates of reflectivity along with their uncertainty. I demonstrate that the method outlined above works well and - thus - paves the way to large-scale seismic exploration of the lowermost mantle. With the new technology I mapped the structure at and near the CMB beneath Central and North America. Several interfaces are detected, and some of them are consistent with expectations from phase transformations in Magnesiiim perovskite. If we know which interface is associated with a particular phase transformation, and if we know the thermodynamic (P-T) relations of the stability fields of the phases, then we can estimate temperature from the pressure as inferred from the depth at which the transition occurs in the seismic sections. Here we associate a seismically observed wavespeed increase with the perovskite to post-perovskite transition and a wavespeed decrease with the back transformation to perovskite.

Department dc:contributor.department

Massachusetts Institute of Technology. Department of Earth, Atmospheric, and Planetary Sciences

Grantor dc:publisher

Massachusetts Institute of Technology

Year dc:date.issued

2007

Author dc:creator

• Wang, Ping

Advisor dc:contributor.advisor

• Robert D. Van der Hilst and Maarten V. de Hoop.

• Earth, Atmospheric, and Planetary Sciences.

Statement dc:rights

• M.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission.

Licence dc:rights.uri

• http://dspace.mit.edu/handle/1721.1/7582

Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/1721.1/40966

OAI identifier oai:identifier

oai:dspace.mit.edu:1721.1/40966