Comparison of fiber-optic sensor and borehole seismometer VSP surveys in a scientific borehole: DFDP-2b, Alpine Fault, New Zealand

Constantinou, Alexis; Schmitt, Douglas R.; Kofman, R.; Kellett, Richard; Eccles, J. D.; Lawton, Donald C.; Bertram, Malcolm B.; Hall, Kevin; Townend, John; Savage, M. K.; Buske, Stefan; Lay, Vera; Gorman, A. R.

doi:10.1190/segam2016-13946302.1

Cited by 12 publications

(22 citation statements)

References 5 publications

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“…Note that the signal‐to‐noise‐ratio in Figure f is better than that in Figure e, presumably due to the smaller offset. Already in this comparison, the good fit between the two types of recordings is visible as discussed by Constantinou et al () in more detail. Due to loose casing, the shallow part of the borehole shows strong ringing up to a depth of about 70 m and was not used for velocity analysis.…”

Section: Velocity Model Constructionsupporting

confidence: 63%

“…A zero‐offset VSP survey was undertaken to obtain a detailed image of the subsurface surrounding the borehole and to be able to directly correlate with borehole logging results (e.g., the sonic log results of Jeppson, ; Townend et al, ) and reflection seismic images. Additionally, we are able to compare both methods (DVS and conventional three‐component recordings), extending the preliminary analysis conducted by Constantinou et al (). The source point was positioned 23 m southeast of the top of the borehole.…”

Section: Seismic Data Acquisitionmentioning

confidence: 58%

“…The three‐component Sercel tool was shifted to allow the wavefield to be obtained at 311 points from z =1to 299 m depth (bsl) at 1 m spacing. In contrast, the hDVS provided samples from z =−95 to 723 m at a nominal spacing of 2 m (Constantinou et al, ; Townend et al, ).…”

Section: Seismic Data Acquisitionmentioning

confidence: 99%

“…The vertical resolution along the borehole can be expected to be a lot better with a geophone spacing as low as 1 m for the Sercel tool. This is taken into account by separate analysis, for example, by zero‐offset velocity profiles from Constantinou et al (). In the obtained blended velocity model, small‐scale heterogeneities will not be resolved but will contribute to a mismatch between picked and modeled traveltimes.…”

Section: Velocity Model Constructionmentioning

confidence: 99%

“…However, a fiber optic cable was successfully installed along the length of the borehole. The fiber has since been used to conduct repeated temperature surveys (Janku‐Capova et al, ) and seismic imaging using a version of distributed acoustic sensing known as distributed heterodyne vibration sensing (Constantinou et al, ).…”

Section: Introductionmentioning

confidence: 99%

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Seismic P Wave Velocity Model From 3‐D Surface and Borehole Seismic Data at the Alpine Fault DFDP‐2 Drill Site (Whataroa, New Zealand)

et al. 2020

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The New Zealand Alpine Fault is a major plate boundary that is expected to be close to rupture, allowing a unique study of fault properties prior to a future earthquake. Here we present 3-D seismic data from the DFDP-2 drill site in Whataroa to constrain valley structures that were obscured in previous 2-D seismic data. The new data consist of a 3-D extended vertical seismic profiling (VSP) survey using three-component and fiber optic receivers in the DFDP-2B borehole and a variety of receivers deployed at the surface. The data set enables us to derive a detailed 3-D P wave velocity model by first-arrival traveltime tomography. We identify a 100-460 m thick sediment layer (mean velocity 2,200 ± 400 m/s) above the basement (mean velocity 4,200 ± 500 m/s). Particularly on the western valley side, a region of high velocities rises steeply to the surface and mimics the topography. We interpret this to be the infilled flank of the glacial valley that has been eroded into the basement. In general, the 3-D structures revealed by the velocity model on the hanging wall of the Alpine Fault correlate well with the surface topography and borehole findings. As a reliable velocity model is not only valuable in itself but also crucial for static corrections and migration algorithms, the Whataroa Valley P wave velocity model we have derived will be of great importance for ongoing seismic imaging. Our results highlight the importance of 3-D seismic data for investigating glacial valley structures in general and the Alpine Fault and adjacent structures in particular.Viewed on a regional scale, the central Alpine Fault appears as a straight boundary (e.g., Norris & Cooper, 2001;Sutherland et al., 2006). Crustal-scale seismic reflection data show a single oblique fault striking northeastward and dipping 40−60 • to the southeast at depths of 15-30 km (e.g., Davey et al.

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Section: Velocity Model Constructionsupporting

confidence: 63%

Section: Seismic Data Acquisitionmentioning

confidence: 58%

Section: Seismic Data Acquisitionmentioning

confidence: 99%

Section: Velocity Model Constructionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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