P-wave velocity structures under South America from multi-frequency tomography

Thesis

This thesis presents P-wave tomographic images of mantle structures under South America and offers tectonic interpretations for the recovered features. To build this inversion, source time functions, a requirement for computing suitably realistic synthetic seismograms, were estimated from broadband waveforms of 3505 teleseismic earthquakes of magnitudes greater than 5.6, recorded between 1990 and 2016 by regional and global networks. Almost 5M traveltime anomalies were calculated using cross-correlation of synthetic and observed seismograms in eight frequency bands, with centre periods ranging from 30.0 to 2.7 seconds. Sensitivity kernels were calculated using finite-frequency theory. In order to better illuminate weakly sampled mantle regions, integrated traveltime picks from the International Seismological Centre's ISC-EHB catalogue were also included.

Two main features are inferred from the tomographic images under South America. First, extensive lower-mantle fast anomalies under north-western region of South America may indicate ancient intra-oceanic subduction settings, which might have occurred to the west of the western margin of the continent. Secondly, high velocity provinces beneath western margin of South America, which appears only in the upper mantle, is interpreted to imply a younger subduction history. This fast anomalies distribution is associated to the Andean segmentation which has been archived in the geological records.

Authors: Mohammadzaheri, A

• DOI: 10.5287/ora-norvpzqr4
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Language: English