Imaging the lowermost mantle (D ") beneath the Pacific Ocean with SKKS coda waves

We apply a generalized Radon transform (GRT) to SKKS data to obtain a large-scale high-resolution image of the lowermost mantle (400 kilometers above the core-mantle boundary) beneath the Pacific Ocean (125° E-75°W, 45° S-65°N in this work). More than 4,000,000 radial teleseismic traces from about 8,000 events (mb >= 5.8) between 1990 and 2015, globally recorded by one or more of a total ~27,000 receivers, were collected from IRIS-DMC. All of the traces were automatically band-pass filtered (10s to 50s), rotated, clustered, deconvoluted, and finally migrated to structural reflectivity profiles using reference wavespeeds according to the iasp91 model. We compare the 2D and 3D imaging results beneath the Pacific subduction zones and the non-subducting regions, including the southeastern Pacific and Hawaii, focusing on the positive velocity contrast above the CMB that might delineate the D" discontinuity. We observe broad zones of scatter surfaces, which may indicate multiple-interface post-perovskite phase transitions caused by compositionally differentiated subducted lithosphere. Furthermore, we observe a sharp change in the proposed multiple-interface structure regarding the total number of positive interfaces, the intervals, and the overall pattern of the anomalies from the subduction zones to the non-subducting regions. Such structural complexity implies: (1) the presence of old (at least 180 Ma) subducted material layer of either continental or oceanic lithosphere under the whole Pacific Ocean; and (2) spatial variations in iron, magnesium, and silica components in the subducted lithosphere. Understanding the possible relationship between observed complexity and composition requires further interdisciplinary research.

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

2015

Author dc:creator

• Yu, Zhulin

Advisor dc:contributor.advisor

• Robert D. van der Hilst.

• 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/1721.1/101342

OAI identifier oai:identifier

oai:dspace.mit.edu:1721.1/101342