Three-component digital-based seismic landstreamer: Methodologies for infrastructure planning applications

  • Datum: 02 februari, kl. 10.00
  • Plats: Hambergsalen, Geocentrum, Villavagen 16, Uppsala
  • Doktorand: Brodic, Bojan
  • Om avhandlingen
  • Arrangör: Geofysik
  • Kontaktperson: Brodic, Bojan
  • Disputation

Studies conducted in this thesis demonstrate the landstreamer’s potential for various near-surface applications and show the benefits and need for 3C seismic data recording.

To support urban infrastructure planning projects, along with various other near-surface applications, a multicomponent landstreamer was developed. The landstreamer was built with broadband (0-800 Hz), three-component (3C) micro-electro-mechanical system (MEMS) sensors. The digital nature of the MEMS sensors makes the developed landstreamer insensitive to electric/electromagnetic noise.

The landstreamer’s design and its seismic imaging capabilities, along with the MEMS technical specifications, were evaluated in several studies. When comparing signals recorded with the streamer with planted MEMS sensors, no negative effects of the design were noted. Compared to different geophones tested, the streamer produced higher quality and broader signal bandwidth data. Additionally, a seismic study conducted in a tunnel demonstrated its electric/electromagnetic noise insensitivity. The streamer combined with wireless seismic recorders was used to survey logistically challenging areas for improved imaging and characterizations and avoid interference with traffic.

For example, at the Stockholm Bypass site, the landstreamer recorded data were used for traveltime tomography with results showing a well delineated bedrock level and potential low-velocity zones matching with inferred poor-quality-class rocks. The seismic response of fractures and their extent between a tunnel and the surface was studied at the Äspö Hard Rock Laboratory site. The velocity model obtained using the traveltime tomography approach showed known well-characterized fracture systems and potential additional formerly unknown ones. Additionally, compressional- and shear-wave velocities, seismic quality factors, Vp/Vs and dynamic Poisson’s ratios of the known fracture zones were obtained. Fractures and/or weakness zones in the bedrock were imaged using refraction and reflection imaging methods at a site contaminated with a cancerogenic pollutant in southwest Sweden, illustrating the potential of the streamer for environmental-related applications. In southern Finland, the landstreamer was used for SH-wave reflection seismic imaging from a vertically oriented impact source with the results showing a well-delineated bedrock level and weak reflections correlating well with geology. At the same site, its potential for multichannel analysis of surface waves (MASW) was demonstrated. The surface-wave obtained shear-wave velocities match well with the borehole based stratigraphy of the site and are complementary to the SH-wave reflectivity and previous investigations at the site.