Passive Multichannel Analysis of Surface Waves (MASW) - study over salt dissolution voids

Birgit Leitner

Research output: ThesisDoctoral Thesis

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Abstract

The passive Multichannel Analysis of Surface Waves (MASW) provides information about the shear wave velocity structure of the subsurface by using background noise (traffic, wind, etc.) as seismic source. Especially sensible areas profit from the fact that no additional vibrations have to be performed. Furthermore, the sources used in passive MASW provide signals with lower frequencies, which enable higher investigation depths. For these characteristics the passive MASW method is mainly applied in this study. A former salt dissolution-mining field in Hutchinson, Kansas (USA) is the testing area used in this study. In succession of excessive mining, voids formed in the subsurface and in some cases, as a consequence of migrating processes, sink holes. As the former mining field borders directly on the city and is intersected by a busy railroad line, some of the former production wells have been chosen, to investigate existing voids underneath and classify their risk of collapse, by determining the shear wave velocity and indirectly, the stress/strain conditions over the voids. The study exposes on the one hand developments of the passive MASW method and on the other hand the study reveals the condition of different migrating voids and their surroundings, with the help of the new developments in the method. The real datasets of Hutchinson were processed with the aid of the program SurfSeis® and further software developed as part of this study. To obtain an optimal result in resolution, depth of investigation and in the amount of depth profiles, a 2D receiver array is necessary. With the 2D spread it is possible to locate the direction of the recorded energy. From the overall array several sub-arrays were selected. The sub-arrays have receivers within a narrow rectangle that is orientated towards the maximum incoming energy. The signals of each rectangle are stacked over narrow limits around the azimuth of maximum incoming energy. The trains as passive sources produced signals with frequencies down to 3.5Hz and due to the developments of the passive MASW method the signals could be resolved and investigation depths up to 70m were achieved (active MASW limit in the Hutchinsons area approx. 20m). An obvious difference in the shear wave velocities and subsequently in the stress field were determined, between areas with voids underneath and analogy terrains with no voids underneath. Also evidences for an existence of galleries between voids could be detected. A differentiation for a relative risk of collapse between the investigated locations was possible.
Translated title of the contributionPassive Multichannel Analysis of Surface Waves (MASW) - Untersuchungen oberhalb von Salzlösungs Hohlräumen
Original languageEnglish
QualificationDr.mont.
Supervisors/Advisors
  • Millahn, Karl, Assessor A (internal)
  • Scholger, Robert, Assessor B (internal)
Publication statusPublished - 2015

Bibliographical note

embargoed until null

Keywords

  • MASW
  • Multichannel Analysis of Surface Waves
  • passive source
  • Surface Waves
  • Rayleigh Waves
  • salt dissolution voids
  • Engineering Geophysics

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