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Tomographic inversion of P410s delay times for simultaneous determination of P and S velocities of the upper mantle beneath the Baltic Shield
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences.
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences.
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences.
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences.
2007 (English)In: Physics of the Earth and Planetary Interiors, ISSN 0031-9201, E-ISSN 1872-7395, Vol. 160, no 2, 157-168 p.Article in journal (Refereed) Published
Abstract [en]

Teleseismic data recorded by stations in the Swedish National Seismic Network (SNSN) are used for a study of upper mantle structure beneath the Baltic Shield using the receiver function technique. The data show very clear conversions from the 410 and 660 km discontinuities. The signals associated with P to S conversions at these discontinuities arrive 1–2 s earlier than predicted by global models such as IASP91 or PREM. We interpret this as a manifestation of higher than average velocities in the mantle beneath the shield, consistent with lower than average global temperatures. For a 1400 km profile along the network, we observe variations of around 1 second in delay times of P410s and slightly less for P660s. Under the assumption that the mantle discontinuities are at a given constant depth, the delay times of the mantle converted phases are tomographically inverted to reveal P and S velocity structure below the stations. Synthetic tests show that this tomographic inversion has the potential to resolve P and S velocity variations at structural scales adequate for upper mantle studies. Results from application to real data appear to be consistent with independently produced mantle velocity structures deduced from normal tomographic arrival time data. For the P velocity model, a north-dipping body of (relatively) low velocity is found for the central part of the profile at 58–64°N. A sharp contrast from low to high velocities that may be associated with the Proterozoic–Archean boundary is found at 66°N.

Place, publisher, year, edition, pages
2007. Vol. 160, no 2, 157-168 p.
Keyword [en]
Baltic Shield, Inversion, Receiver function, Seismology, Tomography
National Category
Earth and Related Environmental Sciences
Identifiers
URN: urn:nbn:se:uu:diva-96023DOI: 10.1016/j.pepi.2006.11.005ISI: 000243738200005OAI: oai:DiVA.org:uu-96023DiVA: diva2:170431
Available from: 2007-05-10 Created: 2007-05-10 Last updated: 2017-12-14Bibliographically approved
In thesis
1. Analyses of Seismic Wave Conversion in the Crust and Upper Mantle beneath the Baltic Shield
Open this publication in new window or tab >>Analyses of Seismic Wave Conversion in the Crust and Upper Mantle beneath the Baltic Shield
2007 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Teleseismic data recorded by broad-band seismic stations in the Swedish National Seismic Network (SNSN) have been used in a suite of studies of seismic wave conversion in order to assess the structure of the crust and upper mantle beneath the Baltic Shield. Signals of seismic waves converted between P and S at seismic discontinuities within the Earth carry information on the velocity contrast at the converting interface, on the depth of conversion and on P and S velocities above this depth.

The conversion from P to S at the crust-mantle boundary (the Moho) provides a robust tool to constrain crustal thicknesses. Results of such analysis for the Baltic Shield show considerable variation of Moho depths and significantly improve the Moho depth map. Analysis of waves converted from S to P in the upper mantle reveals a layered lithosphere with alternating high and low velocity bodies. It also detects clear signals of a sharp velocity contrast at the lithosphere-asthenosphere boundary at depths around 200 km.

Delay times of P410s, the conversion from P to S at the upper mantle discontinuity at 410 km depth, were used in a tomographic inversion to simultaneously determine P and S velocities in the upper mantle. The polarisation of P410s was also used to study anisotropy of the upper mantle. Results of these analyses are found to be in close agreement with independently derived results from arrival time tomography and shear-wave splitting analysis of SKS.

The results presented in this thesis demonstrate the ability of converted wave analysis as a tool to detect and image geological boundaries that involve sharp contrasts in seismic properties. The results also show that this analysis can provide means of studying aspects of Earth’s structure that are conventionally studied using other types of seismic data.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2007. 50 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 319
Keyword
Geophysics, converted waves, Moho, upper mantle, Baltic Shield, tomography, anisotropy, receiver function, Geofysik
National Category
Geophysics
Identifiers
urn:nbn:se:uu:diva-7930 (URN)978-91-554-6919-1 (ISBN)
Public defence
2007-06-15, Axel Hambergsalen, Geocentrum, Villavägen 16, Uppsala, 10:00
Opponent
Supervisors
Available from: 2007-05-10 Created: 2007-05-10 Last updated: 2016-05-13Bibliographically approved

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