Staggered or adapted grids for seismic tomography?

Vesnaver, Aldo; Böhm, Gualtiero

doi:10.1190/1.1438762

Cited by 84 publications

(45 citation statements)

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“…To increase the nominal resolution of the inversion, the staggered grid method is applied [Vesnaver and Böhm, 2000]. It averages the velocity values obtained from different inversions of a regular coarse gridded model, slightly shifted in space, both in horizontal and vertical directions.…”

Section: Numerical Example Of the Attenuation Inversion Based On An Amentioning

confidence: 99%

Rapid field application of hydraulic tomography for resolving aquifer heterogeneity in unconsolidated sediments

Brauchler

et al. 2013

Water Resources Research

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[1] A new framework is introduced for hydraulic tomography application and validation in the field. Our motivation is the need for methods that are both efficient and expressive for resolving the spatial distribution of heterogeneous hydraulic properties in aquifers. The presented strategy involves time-efficient field experiments and a computationally efficient inversion scheme. By exploiting the early travel time diagnostics of the hydraulic pressure pulses recorded during tomographic cross-well tests, and new application of attenuation inversion, only short-term pumping tests are required. Many of these can be conducted in one day. The procedure is developed by a numerical experiment with a highly heterogeneous aquifer analogue and then applied to a field case with a shallow, unconsolidated sedimentary aquifer, the Stegem€ uhle site in Germany. It is demonstrated that the performance of a suite of tomographic short-term pumping tests, data processing and inversion for the reconstruction of heterogeneous diffusivity and specific storage distribution is possible within one day. Additionally, direct-push injection logging is performed at the field site, and the obtained field data is utilized for successful validation of the hydraulic tomograms. We also compare both methods with respect to the necessary requirements, time demand in the field and complexity of interpretation.Citation: Brauchler, R., R. Hu, L. Hu, S. Jim enez, P. Bayer, P. Dietrich, and T. Ptak (2013), Rapid field application of hydraulic tomography for resolving aquifer heterogeneity in unconsolidated sediments, Water Resour.

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Section: Numerical Example Of the Attenuation Inversion Based On An Amentioning

confidence: 99%

Rapid field application of hydraulic tomography for resolving aquifer heterogeneity in unconsolidated sediments

Brauchler

et al. 2013

Water Resources Research

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“…In the subsequent steps, using the results obtained in the previous inversion, the arrivals were inverted assuming the ray path for the diving waves. Afterward, to improve the lateral resolution of the velocity model, the inversion procedure continued utilizing the staggered grid method (Vesnaver and Böhm, 2000) to obtain a final velocity model (Fig. 8) from the near surface.…”

Section: Tomographic Inversionmentioning

confidence: 99%

A crustal seismic profile across Sicily

Accaino

Catalano

Marzo³

et al. 2011

Tectonophysics

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a b s t r a c t a r t i c l e i n f oA crustal reflection seismic profile, more than 100 km long, was recorded across central Sicily, from the Tyrrhenian shore to the Sicily Channel, to understand the deep structures and the collision mechanisms between Europe and Africa and the subsequent geodynamic evolution. The profile was acquired using explosive sources and 240 active channels recorded by a Sercel 408-XL, 24 bits A/D converter, with a 12 km spread and a 24-fold coverage. The data were processed following a non-conventional procedure in order to preserve the relative amplitudes of the reflections and to better investigate the Sicily deep structures down to the Moho. The main highlighted structures are the dramatic flexure of the Iblean crust, the huge, deeper than expected, trough of Caltanissetta consisting of deep seated thrusts and nappes, and the imbricate thrust system of rigid bodies characterizing the northern Maghrebian chain. We designed an ad hoc acquisition and processing in order to highlight these main geological features in the seismic stacked section. Moreover, the deepest parts of the Caltanissetta trough are imaged for the first time, and its bottom is now fixed at more than 7 s TWT. The giant crustal wedge flexuring the Iblean foreland and the Moho geometries are examinated.

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“…A series of inversion is made, with small shifts applied in x and y directions between each inversion. The resulting velocity fields are averaged over a grid with a spacing equal to the x and y shifts to obtain an image that has a higher resolution than the base grid, without the unwanted effect of poor coverage (Vesnaver and Böhm, 2000). We used base grids of 1.2 km cell size, shifted along x and y axis, to obtain a total of 15 different models, from which the resulting velocity fields were averaged to produce a final model with an effective cell width of 120 m in its central region.…”

Section: Inversion For Vp and Vsmentioning

confidence: 99%

Estimation of gas hydrate concentration from multi-component seismic data at sites on the continental margins of NW Svalbard and the Storegga region of Norway

Westbrook

Chand

Rossi

et al. 2008

Marine and Petroleum Geology

119

135

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High-resolution seismic experiments, employing arrays of closely spaced, four-component ocean-bottom seismic recorders, were conducted at a site off western Svalbard and a site on the northern margin of the Storegga slide, off Norway to investigate how well seismic data can be used to determine the concentration of methane hydrate beneath the seabed. Data from P-waves and from S-waves generated by P-S conversion on reflection were inverted for P-and S-wave velocity (Vp and Vs), using 3D travel-time tomography, 2D ray-tracing inversion and 1D waveform inversion. At the NW Svalbard site, positive Vp anomalies above a sea-bottomsimulating reflector (BSR) indicate the presence of gas hydrate. A zone containing free gas up to 150-m thick, lying immediately beneath the BSR, is indicated by a large reduction in Vp without significant reduction in Vs. At the Storegga site, the lateral and vertical variation in Vp and Vs and the variation in amplitude and polarity of reflectors indicate a heterogeneous distribution of hydrate that is related to a stratigraphically mediated distribution of free gas beneath the BSR. Derivation of hydrate content from Vp and Vs was evaluated, using different models for how hydrate affects the seismic properties of the sediment host and different approaches for estimating the background velocity of the sediment host. The error in the average Vp of an interval of 20-m thickness is about 2.5%, at 95% confidence, and yields a resolution of hydrate concentration of about 3%, if hydrate forms a connected framework, or about 7%, if it is both pore-filling and framework-forming. At NW Svalbard, in a zone about 90-m thick above the BSR, a Biot-theory-based method predicts hydrate concentrations of up to 11% of pore space, and an effective-medium-based method predicts concentrations of up to 6%, if hydrate forms a connected framework, or 12%, if hydrate is both pore-filling and frameworkforming. At Storegga, hydrate concentrations of up to 10% or 20% were predicted, depending on the hydrate model, in a zone about 120-m thick above a BSR. With seismic techniques alone, we can only estimate with any confidence the average hydrate content of broad intervals containing more than one layer, not only because of the uncertainty in the layer-by-layer variation in lithology, but also because of the negative correlation in the errors of estimation of velocity between adjacent layers. In this investigation, an interval of about 20-m thickness (equivalent to between 2 and 5 layers in the model used for waveform inversion) was the smallest within which one could sensibly estimate the hydrate content. If lithological layering much thinner than 20-m thickness controls hydrate content, then hydrate concentrations within layers could significantly exceed or fall below the average values derived from seismic data.

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Staggered or adapted grids for seismic tomography?

Cited by 84 publications

References 0 publications

Rapid field application of hydraulic tomography for resolving aquifer heterogeneity in unconsolidated sediments

Rapid field application of hydraulic tomography for resolving aquifer heterogeneity in unconsolidated sediments

A crustal seismic profile across Sicily

Estimation of gas hydrate concentration from multi-component seismic data at sites on the continental margins of NW Svalbard and the Storegga region of Norway

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