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Analysis of waves converted from S to P in 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.
2007 (English)In: Earth and Planetary Science Letters, ISSN 0012-821X, E-ISSN 1385-013X, Vol. 257, no 1-2, 37-46 p.Article in journal (Refereed) Published
Abstract [en]

Teleseismic data recorded by broadband stations of the Swedish National Seismic Network have been used in a study of waves converted from S to P in the uppermost mantle. S to P converted waves are recorded as precursors to the direct S arrival. This enables us to study seismic discontinuities at depths of 100–300 km where the traditional receiver function technique based on P to S conversion fails due to disturbances from crustal reverberations. Clear signals of S to P conversion are seen for several horizons in the 50–200 km depth range. This is interpreted as a layered lithosphere with alternating high and low velocity bodies. A sharp contrast is imaged at depths around 160 km and continuous for almost 1000 km in the southern part of the profile. This structure coincides with the velocity contrast interpreted by several authors as the lower limit of a prominent low velocity zone in the 95 to 160 km depth range. A feature which we identify as the lithosphere–asthenosphere boundary is clearly imaged at depths around 200 km.

Place, publisher, year, edition, pages
2007. Vol. 257, no 1-2, 37-46 p.
Keyword [en]
lithosphere, asthenosphere, Baltic Shield, converted waves, receiver functions
National Category
Earth and Related Environmental Sciences
Identifiers
URN: urn:nbn:se:uu:diva-96022DOI: 10.1016/j.epsl.2007.02.017ISI: 000246858100004OAI: oai:DiVA.org:uu-96022DiVA: diva2:170430
Available from: 2007-05-10 Created: 2007-05-10 Last updated: 2011-02-02Bibliographically 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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