Nature of seismic reflections and velocities from VSP-experiments and borehole measurements at the KTB deep drilling site in southeast Germany

Lüschen, E.; Bram, K.; Söllner, Walter; Sobolev, S. V.

doi:10.1016/s0040-1951(96)00134-5

Cited by 29 publications

(16 citation statements)

References 10 publications

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“…These faults could have caused a local rotation of the stress field. Similar conditions appear below 4000 m where an additional distinct reflector was recognized (Lu¨schen et al 1996). The reflector appears within a homogeneous section of amphibolites and is not related to changing lithology.…”

Section: Fault Zone / Disk-type Relationmentioning

confidence: 60%

Fractographic features on joints in KTB drill cores as indicators of the contemporary stress orientation

Bankwitz¹,

Bankwitz²

1997

Geol Rundsch

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Fractographic features on joints in cores of the superdeep KTB drilling were used to estimate the orientation of the contemporary maximum horizontal stress (S & ). The unique opportunity to investigate cores from a depth down to approximately 8085 m reveals information on in situ stress orientation with increasing depth. We recognized on the cores the main normal stress axes which are reflected by common fractographic pattern on coring-induced fractures, present in all sections. The analysis is based on the symmetry of joint characteristics: 3D (out-of-plane) shape of the joint and surface features of joint planes. The symmetry axes of these joint features are related to the orientation of principal stress, which permits the determination of the orientation of the contemporary maximum and minimum horizontal stress axes (S & O S ), if the core orientation is determined by other methods. For that purpose, the reorientated cores of the pilot borehole (VB) could be used down to 4000 m. The main borehole (HB) cores are generally not reoriented by several reasons. Some investigations were done by members of the KTB laboratory to determine the supposedly northward orientations of HB core sections by comparison with the foliation and of drilling-induced fractures at the borehole wall (using FMI/Formation MicroImager and FMS/Formation MicroScanner log data) and within the core. Independently, the maximum horizontal in situ stress orientation down to 7800 m was determined from drilling-induced vertical joints, and the strike and dip of the foliation from borehole measurements down to ca. 8600 m, carried out by the staff members at the KTB. Additionally, rock fragments from below 9050 m represent a palaeo-tectonic joint system developed at a depth of ca. 9 km.

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Section: Fault Zone / Disk-type Relationmentioning

confidence: 60%

Fractographic features on joints in KTB drill cores as indicators of the contemporary stress orientation

Bankwitz¹,

Bankwitz²

1997

Geol Rundsch

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“…Here, the interval velocity profiles deduced from sonic and VSP measurements show an even stronger velocity gradient for gneisses in the uppermost 1000 m of the KTB borehole (Lüschen et al 1996). Another example can be found in Alberta (Canada) where the interval velocities from VSP measurements reveal an increasing velocity with depth from approximately 5500 to 6500 m s −1 for the crystalline basement rocks (granitoids, gneisses, metasediments) of the Canadian Shield (Chan & Schmitt 2015).…”

Section: Vertical Velocity Gradientmentioning

confidence: 63%

The derivation of an anisotropic velocity model from a combined surface and borehole seismic survey in crystalline environment at the COSC-1 borehole, central Sweden

Simon

Buske

Krauß

et al. 2017

Geophysical Journal International

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. (2017): The derivation of an anisotropic velocity model from a combined surface and borehole seismic survey in crystalline environment at the COSC-1 borehole, central Sweden. -Geophysical Journal International, 210, 3, pp. 1332-1346 S U M M A R YThe Scandinavian Caledonides provide a well-preserved example of a Palaeozoic continentcontinent collision, where surface geology in combination with geophysical data provides information about the geometry of parts of the Caledonian structure. The project COSC (Collisional Orogeny in the Scandinavian Caledonides) investigates the structure and physical conditions of the orogen units and the underlying basement with two approximately 2.5 km deep cored boreholes in western Jämtland, central Sweden. In 2014, the COSC-1 borehole was successfully drilled through a thick section of the Seve Nappe Complex. This tectonostratigraphic unit, mainly consisting of gneisses, belongs to the so-called Middle Allochthons and has been ductilely deformed and transported during the collisional orogeny. After the drilling, a major seismic survey was conducted in and around the COSC-1 borehole with the aim to recover findings on the structure around the borehole from core analysis and downhole logging. The survey comprised both seismic reflection and transmission experiments, and included zero-offset and multiazimuthal walkaway Vertical Seismic Profile (VSP) measurements, three long offset surface lines centred on the borehole, and a limited 3-D seismic survey. In this study, the data from the multiazimuthal walkaway VSP and the surface lines were used to derive detailed velocity models around the COSC-1 borehole by inverting the first-arrival traveltimes. The comparison of velocities from these tomography results with a velocity function calculated directly from the zero-offset VSP revealed clear differences in velocities for horizontally and vertically travelling waves. Therefore, an anisotropic VTI (transversely isotropic with vertical axis of symmetry) model was found that explains first-arrival traveltimes from both the surface and borehole seismic data. The model is described by a vertical P-wave velocity function derived from zero-offset VSP and the Thomsen parameters = 0.03 and δ = 0.3, estimated by laboratory studies and the analysis of the surface seismic and walkaway VSP data. This resulting anisotropic model provides the basis for further detailed geological and geophysical investigations in the direct vicinity of the borehole.

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“…12a). The standard vertical seismic measurement (VSP) provided a reliable depth assignment nearby KTB site to interpreted surface seismic data (Lüschen et al 1996). The more sophisticated moving source profiling (MSP) measurements recorded azimuthal variations of the wave propagation in a 7.5 km vicinity of the KTB bore holes and could provide data for assessing the anisotropic behavior of the adjacent rock units-see Rabbel et al (2004) and Okaya et al (2004) for technical details.…”

Section: Influence Of Anisotropy At Ktb Sitementioning

confidence: 99%

Depth-Recursive Tomography Along the Eger Rift Using the S01 Profile Refraction Data: Tested at the KTB Super Drilling Hole, Structural Interpretation Supported by Magnetic, Gravity and Petrophysical Data

et al. 2009

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The refraction data from the SUDETES 2003 experiment were used for highresolution tomography along the profile S01. The S01 profile crosses the zone ErbendorfVohenstrauss (ZEV) near the KTB site, then follows the SW-NE oriented Eger Rift in the middle part and continues toward the NE across the Elbe zone and the Sudetic structures as far as the Trans-European Suture Zone. To get the best resolution in the velocity image only the first arrivals of Pg waves with minimum picking errors were used. The previous depth-recursive tomographic method, based on Claerbout's imaging principle, has been adapted to perform the linearized inversions in iterative mode. This innovative DRTG method (Depth-Recursive Tomography on Grid) uses a regular system of refraction rays covering uniformly the mapped domain. The DRTG iterations yielded a fine-grid velocity model with a required level of RMS travel-time fit and the model roughness. The traveltime residuals, assessed at single depth levels, were used to derive the statistical lateral resolution of ''lens-shaped'' velocity anomalies. Thus, for the 95% confidence level and 5% anomalies, one can resolve their lateral sizes from 15 to 40 km at the depths from 0 to 20 km. The DRTG tomography succeeded in resolving a significant low-velocity zone (LVZ) bound to the Franconian lineament nearby the KTB site. It is shown that the next optimization of the model best updated during the DRTG iterations tends to a minimumfeature model with sweeping out any LVZs. The velocities derived by the depth-recursive tomography relate to the horizontal directions of wave propagation rather than to the vertical. This was proved at the KTB site where pronounced anisotropic behavior of a steeply tilted metamorphic rock complex of the ZEV unit has been previously determined. Involving a *7% anisotropy observed for the ''slow'' axis of symmetry oriented coincidentally in the horizontal SW-NE direction of the S01 profile, the DRTG velocity model agrees fairly well with the log velocities at the KTB site. Comparison with the reflectivity map obtained on the reflection seismic profile KTB8502 confirmed the validity of DRTG velocity model at maximum depths of *16 km. The DRTG tomography enabled us to follow the relationship of major geological units of Bohemian Massif as they manifested in the obtained P-wave velocity image down to 15 km. Although the contact of Saxothuringian and the Teplá-Barrandian Unit (TBU) is collateral with the S01 profile direction, several major tectonic zones are rather perpendicular to the Variscan strike and so fairly imaged in the S01 cross-section. They exhibit a weak velocity gradient of sub-horizontal directions within the middle crust. In particular, the Moldanubian and TBU contact beneath the Western Krušné hory/Erzgebirge Pluton, the buried contact of the Lusatia unit and the TBU within the Elbe fault zone were identified. The maxima on the 6,100 ms -1 isovelocity in the middle crust delimitated the known ultrabasic Erbendorf complex and implied also two next ultrabasic massi...

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Nature of seismic reflections and velocities from VSP-experiments and borehole measurements at the KTB deep drilling site in southeast Germany

Cited by 29 publications

References 10 publications

Fractographic features on joints in KTB drill cores as indicators of the contemporary stress orientation

Fractographic features on joints in KTB drill cores as indicators of the contemporary stress orientation

The derivation of an anisotropic velocity model from a combined surface and borehole seismic survey in crystalline environment at the COSC-1 borehole, central Sweden

Depth-Recursive Tomography Along the Eger Rift Using the S01 Profile Refraction Data: Tested at the KTB Super Drilling Hole, Structural Interpretation Supported by Magnetic, Gravity and Petrophysical Data

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