Title
Lowermost mantle anisotropy near the eastern edge of the Pacific LLSVP: Constraints from SKS-SKKS splitting intensity measurements
Date Issued
01 August 2017
Access level
metadata only access
Resource Type
journal article
Author(s)
Publisher(s)
Oxford University Press
Abstract
Seismic anisotropy has been documented in many portions of the lowermost mantle, with particularly strong anisotropy thought to be present along the edges of large low shear velocity provinces (LLSVPs). The region surrounding the Pacific LLSVP, however, has not yet been studied extensively in terms of its anisotropic structure. In this study, we use seismic data from southern Peru, northern Bolivia and Easter Island to probe lowermost mantle anisotropy beneath the eastern Pacific Ocean, mostly relying on data from the Peru Lithosphere and Slab Experiment and Central Andean Uplift and Geodynamics of High Topography experiments. Differential shear wave splitting measurements from phases that have similar ray paths in the upper mantle but different ray paths in the lowermost mantle, such as SKS and SKKS, are used to constrain anisotropy in D". We measured splitting for 215 same station-event SKS-SKKS pairs that sample the eastern Pacific LLSVP at the base of the mantle.We used measurements of splitting intensity(SI), a measure of the amount of energy on the transverse component, to objectively and quantitatively analyse any discrepancies between SKS and SKKS phases. While the overall splitting signal is dominated by the upper-mantle anisotropy, a minority of SKS-SKKS pairs (~10 per cent) exhibit strongly discrepant splitting between the phases (i.e. the waveforms require a difference in SI of at least 0.4), indicating a likely contribution from lowermost mantle anisotropy. In order to enhance lower mantle signals, we also stacked waveforms within individual subregions and applied a waveform differencing technique to isolate the signal from the lowermost mantle. Our stacking procedure yields evidence for substantial splitting due to lowermost mantle anisotropy only for a specific region that likely straddles the edge of Pacific LLSVP. Our observations are consistent with the localization of deformation and anisotropy near the eastern boundary of the Pacific LLSVP, similar to previous observations for the African LLSVP.
Start page
774
End page
786
Volume
210
Issue
2
Language
English
OCDE Knowledge area
Ingeniería oceanográfica
Mecánica aplicada
Oceanografía, Hidrología, Recursos hídricos
Geología
Subjects
Scopus EID
2-s2.0-85037144098
Source
Geophysical Journal International
ISSN of the container
0956540X
Sponsor(s)
Seismic data from the Global Seismograph Network (II), Global Telemetered Seismograph Network (GT), Chilean National Seismic Network (C) and Red Sismologica Nacional (CI) were used in this study, in addition to data from the Peru Lithosphere and Slab Experiment (PULSE) and the Central Andean Uplift and Geodynamics of High Topography (CAUGHT) projects. All data were accessed via the Data Management Center (DMC) of the Incorporated Research Institutions for Seismology (IRIS). We thank the IRIS PASSCAL Instrument Center as well as the many field volunteers for their support of the PULSE and CAUGHT projects. This work was supported by the National Science Foundation (NSF) via grant EAR-1550722 (MDL). The PULSE experiment was supported by NSF grants EAR-0944184 (LSW), EAR-0943991 (SLB) and EAR-0943962 (MDL). The CAUGHT experiment was supported by NSF grants EAR-0908777 (LSW) and EAR-0907880 (SLB and GZ). Some figures were prepared using the Generic Mapping Tools (Wessel and Smith 1991). We are grateful to two anonymous reviewers for thoughtful and constructive suggestions that improved the paper.
Sources of information:
Directorio de Producción Científica
Scopus