scholarly journals Integrated Geophysical Analyses of Shallow-Water Seismic Imaging With Scholte Wave Inversion: The Northern Adriatic Sea Case Study

2020 ◽  
Vol 8 ◽  
Author(s):  
M. Giustiniani ◽  
U. Tinivella ◽  
S. Parolai ◽  
F. Donda ◽  
G. Brancolini ◽  
...  
Keyword(s):  
Shallow Water ◽  
Seismic Data ◽  
Seismic Imaging ◽  
P Wave ◽  
Critical Conditions ◽  
Integrated Analysis ◽  
Northern Adriatic Sea ◽  
Northern Adriatic ◽  
Time Migration ◽  
Scholte Waves

The integrated analysis using different seismic wave types in a record is a very efficient approach for a comprehensive characterization of marine sediments, especially in shallow water conditions. The proposed integrated method to analyze seismic data in post-critical conditions consists of: 1) the inversion of Scholte waves to obtain a reliable Vs distribution of the near seafloor; 2) pre-processing of seismic data; 3) construction of the P-wave velocity field by using all available information, including available well data; and 4) the application of the wave equation datuming and post-processing, such as pre-stack time migration. We demonstrate how this approach could be successfully applied on seismic datasets characterized by post-critical conditions and the occurrence of the Scholte waves, which may be exploited to provide fundamental information instead of being only an unwanted effect. The integrated analysis of seismic events can thus help, together with data processing, by providing better seismic imaging, which is a priority for a reliable seismostratigraphic interpretation.

On plane‐wave decomposition: Alias removal

Geophysics ◽  
1989 ◽  
Vol 54 (10) ◽  
pp. 1339-1343 ◽  
Author(s):  
S. C. Singh ◽  
G. F. West ◽  
C. H. Chapman
Keyword(s):  
Plane Wave ◽  
Seismic Data ◽  
P Wave ◽  
S Wave ◽  
Plane Wave Decomposition ◽  
Time Migration ◽  
Time Distance ◽  
P Domain ◽  
Wave Decomposition ◽  
Rapid Modeling

The delay‐time (τ‐p) parameterization, which is also known as the plane‐wave decomposition (PWD) of seismic data, has several advantages over the more traditional time‐distance (t‐x) representation (Schultz and Claerbout, 1978). Plane‐wave seismograms in the (τ, p) domain can be used for obtaining subsurface elastic properties (P‐wave and S‐wave velocities and density as functions of depth) from inversion of the observed oblique‐incidence seismic data (e.g., Yagle and Levy, 1985; Carazzone, 1986; Carrion, 1986; Singh et al., 1989). Treitel et al. (1982) performed time migration of plane‐wave seismograms. Diebold and Stoffa (1981) used plane‐wave seismograms to derive a velocity‐depth function. Decomposing seismic data also allows more rapid modeling, since it is faster to compute synthetic seismograms in the (τ, p) than in the (t, x) domain. Unfortunately, the transformation of seismic data from the (t, x) to the (τ, p) domain may produce artifacts, such as those caused by discrete sampling, of the data in space.

scholarly journals On the feasibility of the use of wind SAR to downscale waves on shallow water

Ocean Science ◽  
2016 ◽  
Vol 12 (1) ◽  
pp. 39-49 ◽  
Author(s):  
O. Q. Gutiérrez ◽  
F. Filipponi ◽  
A. Taramelli ◽  
E. Valentini ◽  
P. Camus ◽  
...  
Keyword(s):  
Shallow Water ◽  
Spatial Resolution ◽  
Water Waves ◽  
Wave Climate ◽  
Wind Fields ◽  
Northern Adriatic Sea ◽  
Northern Adriatic ◽  
Wave Fields ◽  
Wind Regimes ◽  
Offshore Wave

Abstract. In recent years, wave reanalyses have become popular as a powerful source of information for wave climate research and engineering applications. These wave reanalyses provide continuous time series of offshore wave parameters; nevertheless, in coastal areas or shallow water, waves are poorly described because spatial resolution is not detailed. By means of wave downscaling, it is possible to increase spatial resolution in high temporal coverage simulations, using forcing from wind and offshore wave databases. Meanwhile, the reanalysis wave databases are enough to describe the wave climate at the limit of simulations; wind reanalyses at an adequate spatial resolution to describe the wind structure near the coast are not frequently available. Remote sensing synthetic aperture radar (SAR) has the ability to detect sea surface signatures and estimate wind fields at high resolution (up to 300 m) and high frequency. In this work a wave downscaling is done on the northern Adriatic Sea, using a hybrid methodology and global wave and wind reanalysis as forcing. The wave fields produced were compared to wave fields produced with SAR winds that represent the two dominant wind regimes in the area: the bora (ENE direction) and sirocco (SE direction). Results show a good correlation between the waves forced with reanalysis wind and SAR wind. In addition, a validation of reanalysis is shown. This research demonstrates how Earth observation products, such as SAR wind fields, can be successfully up-taken into oceanographic modeling, producing similar downscaled wave fields when compared to waves forced with reanalysis wind.

scholarly journals LEAST-SQUARE REVERSE TIME MIGRATION (LSRTM) IN THE SHOT DOMAIN

2016 ◽  
Vol 34 (3) ◽  
Author(s):  
Antonio Edson Lima de Oliveira ◽  
Reynam Da Cruz Pestana ◽  
Adriano Wagner Gomes dos Santos
Keyword(s):  
Iterative Method ◽  
Seismic Data ◽  
Seismic Imaging ◽  
Imaging Techniques ◽  
Least Square ◽  
Subsurface Imaging ◽  
Reverse Time ◽  
Reverse Time Migration ◽  
Imaging Methods ◽  
Time Migration

ABSTRACT. One of the major limitations of imaging methods is, usually, the incomplete recorded seismic data that cause difficulties for the subsurface imaging techniques...Keywords: seismic imaging, resolution, modeling, iterative method, computational coast. RESUMO. Uma das limitações das técnicas de imageamento é que, via de regra, os dados sísmicos registrados são incompletos. Isso impossibilita uma correta reconstituição dos refletores em subsuperfície...Palavras-chave: imageamento sísmico, resolução, modelagem, método iterativo, custo computacional.

3D seismic imaging of the Alpine Fault and the glacial valley at Whataroa, New Zealand

2021 ◽  
Author(s):  
Vera Lay ◽  
Stefan Buske ◽  
Franz Kleine ◽  
John Townend ◽  
Richard Kellett ◽  
...  
Keyword(s):  
New Zealand ◽  
Fault Zone ◽  
Seismic Data ◽  
Seismic Imaging ◽  
P Wave ◽  
Seismic Survey ◽  
Fault System ◽  
3D Seismic ◽  
Alpine Fault ◽  
Drill Site

<p>The Alpine Fault at the West Coast of the South Island (New Zealand) is a major plate boundary that is expected to rupture in the next 50 years, likely as a magnitude 8 earthquake. The Deep Fault Drilling Project (DFDP) aimed to deliver insight into the geological structure of this fault zone and its evolution by drilling and sampling the Alpine Fault at depth. Here we present results from a seismic survey around the DFDP-2 drill site in the Whataroa Valley where the drillhole almost reached the fault plane. This unique 3D seismic survey includes several 2D lines and a 3D array at the surface as well as borehole recordings. Within the borehole, the unique option to compare two measurement systems is used: conventional three-component borehole geophones and a fibre optic cable (heterodyne Distributed Vibration Sensing system (hDVS)). Both systems show coherent signals but only the hDVS system allowed a recording along the complete length of the borehole.</p><p>Despite the challenging conditions for seismic imaging within a glacial valley filled with sediments and steeply dipping valley flanks, several structures related to the valley itself as well as the tectonic fault system are imaged. The pre-processing of the seismic data also includes wavefield separation for the zero-offset borehole data. Seismic images are obtained by prestack depth migration approaches.</p><p>Within the glacial valley, particularly steep valley flanks are imaged directly and correlate well with results from the P-wave velocity model obtained by first arrival travel-time tomography. Additionally, a glacially over-deepened trough with nearly horizontally layered sediments is identified about 0.5 km south of the DFDP-2B borehole.</p><p>With regard to the expected Alpine fault zone, a set of several reflectors dipping 40-56° to the southeast are identified in a ~600 m wide zone between depths of 0.2 and 1.2 km that is interpreted to be the minimum extent of the damage zone. Different approaches image one distinct reflector dipping at 40°, which is interpreted to be the main Alpine Fault reflector. This reflector is only ~100 m ahead from the lower end of the borehole. At shallower depths (z<0.5 km), additional reflectors are identified as fault segments and generally have steeper dips up to 56°. About 1 km south of the drill site, a major fault is identified at a depth of 0.1-0.5 km that might be caused by the regional tectonics interacting with local valley structures. A good correlation is observed among the separate seismic data sets and with geological results such as the borehole stratigraphy and the expected surface trace of the fault.</p><p>In conclusion, several structural details of the fault zone and its environment are seismically imaged and show the complexity of the Alpine Fault at the Whataroa Valley. Thus, a detailed seismic characterization clarifies the subsurface structures, which is crucial to understand the transpressive fault’s tectonic processes.</p>

scholarly journals Expected Shifts in Nekton Community Following Salinity Reduction: Insights into Restoration and Management of Transitional Water Habitats

Water ◽  
2019 ◽  
Vol 11 (7) ◽  
pp. 1354 ◽  
Author(s):  
Luca Scapin ◽  
Matteo Zucchetta ◽  
Andrea Bonometto ◽  
Alessandra Feola ◽  
Rossella Boscolo Brusà ◽  
...  
Keyword(s):  
Community Structure ◽  
Shallow Water ◽  
Coastal Lagoons ◽  
Venice Lagoon ◽  
Northern Adriatic Sea ◽  
Management Tools ◽  
Important Species ◽  
Northern Adriatic ◽  
Functional Perspective ◽  
Salinity Reduction

A restoration project is planned to take place in the northern Venice lagoon (northern Adriatic Sea, Italy), aiming at introducing freshwater into a confined shallow water lagoon area and recreating transitional water habitats. This work describes the shifts in the nekton (fish and decapods) community structure to be expected following the future salinity decrease in the restoration area. Nekton was sampled at a series of natural shallow water sites located along salinity gradients in the Venice lagoon. A multivariate GLM approach was followed in order to predict species biomass under the salinity and environmental conditions expected after restoration. Biomass of commercially important species, as well as species of conservation interest, is predicted to increase following salinity reduction and habitat changes. From a functional perspective, an increase in biomass of hyperbenthivores-zooplanctivores, hyperbenthivores-piscivores and detritivores is also expected. This study emphasises the efficacy of a predictive approach for both ecological restoration and ecosystem management in transitional waters. By providing scenarios of community structure, the outcomes of this work could be employed in future evaluations of restoration success in the Venice lagoon, as well as to develop management tools to forecast the effects of alterations of salinity regimes in coastal lagoons due to climate change.

Seismic data processing in vertically inhomogeneous TI media

Geophysics ◽  
1997 ◽  
Vol 62 (2) ◽  
pp. 662-675 ◽  
Author(s):  
Tariq Alkhalifah
Keyword(s):  
Seismic Data ◽  
Transversely Isotropic ◽  
Inhomogeneous Media ◽  
P Wave ◽  
Seismic Data Processing ◽  
Time Migration ◽  
Processing Data ◽  
Two Parameters ◽  
Ti Media ◽  
Ray Parameter

The first and most important step in processing data in transversely isotropic (TI) media for which velocities vary with depth is parameter estimation. The multilayer normal‐moveout (NMO) equation for a dipping reflector provides the basis for extending the TI velocity analysis of Alkhalifah and Tsvankin to vertically inhomogeneous media. This NMO equation is based on a root‐mean‐square (rms) average of interval NMO velocities that correspond to a single ray parameter, that of the dipping event. Therefore, interval NMO velocities [including the normal‐moveout velocity for horizontal events, [Formula: see text]] can be extracted from the stacking velocities using a Dix‐type differentiation procedure. On the other hand, η, which is a key combination of Thomsen's parameters that time‐related processing relies on, is extracted from the interval NMO velocities using a homogeneous inversion within each layer. Time migration, like dip moveout, depends on the same two parameters in vertically inhomogeneous media, namely [Formula: see text] and η, both of which can vary with depth. Therefore, [Formula: see text] and ε estimated using the dip dependency of P‐wave moveout velocity can be used for TI time migration. An application of anisotropic processing to seismic data from offshore Africa demonstrates the importance of considering anisotropy, especially as it pertains to focusing and imaging of dipping events.

scholarly journals Broadband Q-Factor Imaging for Geofluid Detection in the Gulf of Trieste (Northern Adriatic Sea)

2021 ◽  
Vol 9 ◽  
Author(s):  
Aldo Vesnaver ◽  
Gualtiero Böhm ◽  
Martina Busetti ◽  
Michela Dal Cin ◽  
Fabrizio Zgur
Keyword(s):  
Adriatic Sea ◽  
Seismic Energy ◽  
P Wave ◽  
Seismic Survey ◽  
Gas Reservoirs ◽  
Northern Adriatic Sea ◽  
Seismic Attribute ◽  
Northern Adriatic ◽  
Gulf Of Trieste ◽  
Impedance Contrast

Seismic surveys allow estimating lithological parameters, as P-wave velocity and anelastic absorption, which can detect the presence of fracture and fluids in the geological formations. Recently, a new method has been proposed for high-resolution imaging of anelastic absorption, which combines a macro-model from seismic tomography with a micro-model obtained by the pre-stack depth migration of a seismic attribute, i.e., the instantaneous frequency. As a result, we can get a broadband image that provides clues about the presence of saturating fluids. When the saturation changes sharply, as for gas reservoirs with an impermeable caprock, the acoustic impedance contrast produces “bright spots” because of the resulting high reflectivity at its top. When the fluid content changes smoothly, the anelastic absorption becomes a good detector, as fluid-filled formations absorb more seismic energy than hard rocks. We apply this method for imaging the anelastic absorption in a regional seismic survey acquired by OGS in the Gulf of Trieste (northern Adriatic Sea, Italy).

Integrated seismic analysis: Kidney area, northern Alberta, Canada

Geophysics ◽  
1989 ◽  
Vol 54 (10) ◽  
pp. 1240-1248 ◽  
Author(s):  
Robert R. Stewart
Keyword(s):  
Seismic Data ◽  
Velocity Structure ◽  
Seismic Analysis ◽  
Region Of Interest ◽  
P Wave ◽  
Well Logs ◽  
Seismic Line ◽  
Time Migration ◽  
Sonic Log ◽  
Northern Alberta

Integrating various seismic data via simultaneous processing or correlation can increase the accuracy and confidence in subsurface images. To this end, a multioffset VSP survey with simultaneous surface recording was acquired in the fall of 1986 near Red Earth, northern Alberta, in the Kidney prospect area. P‐wave vibrators at three locations west of the survey well were recorded by a downhole three‐component geophone at 15 m increments between depths of 225 m and 1570 m and were recorded simultaneously on a 2900 m surface spread of vertical geophones spaced 25 m apart in line with the VSP sources and just west of the well. These data, along with existing seismic lines and well logs, correlated convincingly and were used to increase confidence in the interpretation of the potential reservoir of interest—a Keg River carbonate (KRC) unit. Tomographic procedures (constrained traveltime inversion) were developed to process simultaneously the well logs, VSP, and surface seismic data. These procedures provided a macroscopic seismic interval velocity in depth. This tomographic velocity structure (TVS) was used in poststack depth migration of an existing seismic line over the region of interest. The resulting depth‐migrated section near the well matched the synthetic seismogram (computed in depth from the sonic log) reasonably well in character and depth for most of the major reflectors. The TVS was also used in a fairly conventional processing flow which included poststack time migration, maximum‐likelihood deconvolution, seismic trace inversion, and time‐to‐depth stretching. The final processed pseudosonic section in depth bore considerable resemblance to the sonic log. About 30 m of KRC was measured from the pseudosonic section, while 35 m of KRC was interpreted from the well logs. The pseudosonic section also strongly suggested thinning or discontinuity in the KRC unit on the section around a previously proposed drilling location (1.7 km west of the well). This interpretation was confirmed by another operator’s subsequent drilling at this location, which encountered only 1 m of KRC. The predicted depth of the KRC top (about 1395 m), interpreted from the pseudosonic section at the second well location, was close to the depth (1400 m) on the well logs.

Elastic least-squares reverse time migration with hybrid l1/l2 misfit function

Geophysics ◽  
2017 ◽  
Vol 82 (3) ◽  
pp. S271-S291 ◽  
Author(s):  
Bingluo Gu ◽  
Zhenchun Li ◽  
Peng Yang ◽  
Wencai Xu ◽  
Jianguang Han
Keyword(s):  
Least Squares ◽  
Seismic Data ◽  
Synthetic Data ◽  
Adjoint Equations ◽  
P Wave ◽  
Reverse Time ◽  
Reverse Time Migration ◽  
S Wave ◽  
Time Migration ◽  
Wave Image

We have developed the theory and synthetic tests of elastic least-squares reverse time migration (ELSRTM). In this method, a least-squares reverse time migration algorithm is used to image multicomponent seismic data based on the first-order elastic velocity-stress wave equation, in which the linearized elastic modeling equations are used for forward modeling and its adjoint equations are derived based on the adjoint-state method for back propagating the data residuals. Also, we have developed another ELSRTM scheme based on the wavefield separation technique, in which the P-wave image is obtained using P-wave forward and adjoint wavefields and the S-wave image is obtained using P-wave forward and S-wave adjoint wavefields. In this way, the crosstalk artifacts can be minimized to a significant extent. In general, seismic data inevitably contain noise. We apply the hybrid [Formula: see text] misfit function to the ELSRTM algorithm to improve the robustness of our ELSRTM to noise. Numerical tests on synthetic data reveal that our ELSRTM, when compared with elastic reverse time migration, can produce images with higher spatial resolution, more-balanced amplitudes, and fewer artifacts. Moreover, the hybrid [Formula: see text] misfit function makes the ELSRTM more robust than the [Formula: see text] misfit function in the presence of noise.

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