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Shallow seismic imaging in hard rock environments: An example from the Forsmark potential nuclear waste storage site, Sweden
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences.
Manuscript (Other academic)
URN: urn:nbn:se:uu:diva-92683OAI: oai:DiVA.org:uu-92683DiVA: diva2:165852
Available from: 2005-02-22 Created: 2005-02-22 Last updated: 2013-11-01Bibliographically approved
In thesis
1. High-Resolution Seismics Methods Applied to Till Covered Hard Rock Environments
Open this publication in new window or tab >>High-Resolution Seismics Methods Applied to Till Covered Hard Rock Environments
2005 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Reflection seismic and seismic tomography methods can be used to image the upper kilometer of hard bedrock and the loose unconsolidated sediments covering it. Developments of these two methods and their application, as well as identifying issues concerning their usage, are the main focus of the thesis. Data used for this development were acquired at three different sites in Sweden, in Forsmark 140 km north of Stockholm, in the Oskarshamn area in southern Sweden, and in the northern part of the Siljan Ring impact crater area.

The reflection seismic data were acquired with long source-receiver offsets relative to some of the targeted depths to be imaged. In the initial processing standard steps were applied, but the uppermost part of the sections were not always clear. The longer offsets imply that pre-stack migration is necessary in order to image the uppermost bedrock as clearly as possible. Careful choice of filters and velocity functions improve the pre-stack migrated image, allowing better correlation with near-surface geological information.

The seismic tomography method has been enhanced to calculate, simultaneously with the velocity inversion, optimal corrections to the picked first break travel times in order to compensate for the delays due to the seismic waves passing through the loose sediments covering the bedrock.

The reflection seismic processing used in this thesis has produced high-quality images of the upper kilometers, and in one example from the Forsmark site, the image of the uppermost 250 meters of the bedrock has been improved. The three-dimensional orientation of reflections has been determined at the Oskarshamn site. Correlation with borehole data shows that many of these reflections originate from fracture zones.

The developed seismic tomography method produces high-detail velocity models for the site in the Siljan impact area and for the Forsmark site. In Forsmark, detailed estimates of the bedrock topography were calculated with the use of the developed tomography method.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2005. viii+66 p.
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 19
Geophysics, High-Resolution, Reflection Seismics, Tomography, Nuclear waste repository, Bedrock, Sediments, Geofysik
National Category
urn:nbn:se:uu:diva-4811 (URN)91-554-6162-X (ISBN)
Public defence
2005-03-18, Axel Hambergsalen, Geocentrum, Villavägen 16, Uppsala, 10:00
Available from: 2005-02-22 Created: 2005-02-22 Last updated: 2016-05-13Bibliographically approved

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Juhlin, Christopher
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