TY - THES

T1 - 3D Seismic Tomography of DT-1B Drill Site

AU - Spriggs, Lucas Crozier Sutek

N1 - no embargo

PY - 2024

Y1 - 2024

N2 - Travel time tomography has been utilized to delineate the boundary between crystalline metamorphic lower crustal rocks and quaternary sediments of a site. The area investigated is approximately 50x50m within the Ivrea Verbano Zone (IVZ). The IVZ is a region of significant geological interest due to deep crustal segments that have been uplifted to shallow depths. DIVE (Drilling the Ivrea-Verbano zonE) is an international scientific collaboration, funded by the ICDP, which aims to unravel fundamental inquiries of the IVZ. This is done through drilling 3 drill-holes, one of which is DT-1B located in Ornavasso Italy. In order to characterize the DT-1B drill site, geophysical investigations were conducted prior to the start of drilling activities including Ground Penetrating Radar (GPR), Electrical Resistivity Tomography (ERT), and active-source seismic surveys. The seismic data was acquired as a tightly spaced 3-D rolling spread with the source lines offset from the geophone lines. This source-receiver geometry is not optimal for 2-D seismic refraction profiling and a 3-D refraction travel-time tomography scheme was subsequently used to derive a subset of 2.5-D profiles that span the drilling site. An Eikonal solver was used to generate velocity models and produce theoretical travel-time curves. The starting velocity model utilized velocities derived from first-break analysis and subsurface geometry assumed from the ERT and GPR data results. An RMS error of 4.97ms between the observed and calculated travel-times is achieved after 12 iterations. The final velocity models compare well with the ERT and GPR profiles and the 3D-velocity cube serves as a good starting model for improved seismic reflection imaging.

AB - Travel time tomography has been utilized to delineate the boundary between crystalline metamorphic lower crustal rocks and quaternary sediments of a site. The area investigated is approximately 50x50m within the Ivrea Verbano Zone (IVZ). The IVZ is a region of significant geological interest due to deep crustal segments that have been uplifted to shallow depths. DIVE (Drilling the Ivrea-Verbano zonE) is an international scientific collaboration, funded by the ICDP, which aims to unravel fundamental inquiries of the IVZ. This is done through drilling 3 drill-holes, one of which is DT-1B located in Ornavasso Italy. In order to characterize the DT-1B drill site, geophysical investigations were conducted prior to the start of drilling activities including Ground Penetrating Radar (GPR), Electrical Resistivity Tomography (ERT), and active-source seismic surveys. The seismic data was acquired as a tightly spaced 3-D rolling spread with the source lines offset from the geophone lines. This source-receiver geometry is not optimal for 2-D seismic refraction profiling and a 3-D refraction travel-time tomography scheme was subsequently used to derive a subset of 2.5-D profiles that span the drilling site. An Eikonal solver was used to generate velocity models and produce theoretical travel-time curves. The starting velocity model utilized velocities derived from first-break analysis and subsurface geometry assumed from the ERT and GPR data results. An RMS error of 4.97ms between the observed and calculated travel-times is achieved after 12 iterations. The final velocity models compare well with the ERT and GPR profiles and the 3D-velocity cube serves as a good starting model for improved seismic reflection imaging.

KW - Bohrungen in der Ivrea-Verbano-Zone

KW - Laufzeittomographie

KW - Seismik aktiver Quellen

KW - Geophysikalische Standortcharakterisierung

KW - Drilling the Ivrea-Verbano zonE

KW - Travel-time Tomography

KW - Active-Source Seismics

KW - Geophysical Site Characterization

M3 - Master's Thesis

ER -