Understanding The Mesozoics Beyond Basalt: A Case Study Of Sub-Basalt Imaging

2020 ◽  
Author(s):  
S. Sengupta
Keyword(s):  
Signal To Noise Ratio ◽  
Seismic Energy ◽  
Flood Basalt ◽  
Velocity Model ◽  
Significant Loss ◽  
P Wave ◽  
Deccan Volcanic Province ◽  
Deccan Volcanism ◽  
Impedance Contrast

The Deccan Volcanic Province of India is considered as one of the largest basalts-covered regions in the world, formed due to extensive outpouring of basaltic lavas during Deccan volcanism (∼65 Ma). The sedimentary sequence below the flood basalt is mainly characterized by Mesozoic strata with a varying thickness of 1000 m to 2500 m. It is considered that requisite heat generation due to Deccan Trap volcanism soon after the Cretaceous sedimentation may have acted as a catalyst in hydrocarbon potential in this area (Vardhan et al. 2008). However, it is essentially unexplored because of the limitations of conventional marine streamer P-wave seismic acquisition in imaging the structures both intra-basalt and sub-basalt. The major challenges can be considered as follows: Strong reflections due to high impedance contrasts at the top (and bottom) of the basalts leading to significant loss of transmitted seismic energy; Scattering of energy due to large acoustic impedance contrast at top and bottom of the basalt; Generation of multiples, both surface-related and interbed, from the top and bottom of the basalt, and intra-basalt boundaries, masking genuine primary reflections at the pre-basasediments; Significant attenuation of seismic energy in the basaltic sequences due to its complex internal structure generally causing weak sub-basasignal; Low signal-to-noise ratio creating ambiguity in estimating accurate velocity model of subsurface. This case study demonstrates that, even with legacy marine streamer surveys, an appropriate workflow of combining suitable advanced technologies can help to overcome the long-standing challenges of sub-basalt imaging. The reprocessed data show clear uplift in the sub-basalt imaging and the inversion results validate the quality of the new data in relation to the well logs.

Passive seismic imaging using microearthquakes

Geophysics ◽  
1995 ◽  
Vol 60 (4) ◽  
pp. 1178-1186 ◽  
Author(s):  
M. Reza Daneshvar ◽  
Clarence S. Clay ◽  
Martha K. Savage
Keyword(s):  
Wave Velocity ◽  
Signal To Noise Ratio ◽  
Velocity Model ◽  
P Wave ◽  
Seismic Signals ◽  
Subsurface Structure ◽  
Near Surface ◽  
P Wave Velocity ◽  
Recording Station ◽  
Passive Seismic

We have developed a method of processing seismic signals generated by microearthquakes to image local subsurface structure beneath a recording station. This technique uses the autocorrelation of the vertically traveling earthquake signals to generate pseudoreflection seismograms that can be interpreted for subsurface structure. Processed pseudoreflection data, from microearthquakes recorded in the island of Hawaii, show consistent reflectivity patterns that are interpreted as near‐surface horizontal features. Forward modeling of the pseudoreflection data results in a P‐wave velocity model that shows reasonable agreement with the velocity model derived from a refraction study in the region. Usable signal‐to‐noise ratio is obtained down to 2 s. A shear‐wave velocity model was also generated by applying this technique to horizontal component data.

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).

Shallow diffraction imaging in an SH-wave crosshole configuration

Geophysics ◽  
2017 ◽  
Vol 82 (1) ◽  
pp. S9-S18 ◽  
Author(s):  
Ariel Lellouch ◽  
Moshe Reshef
Keyword(s):  
Model Building ◽  
Signal To Noise Ratio ◽  
Velocity Model ◽  
Analysis Data ◽  
P Wave ◽  
Image Point ◽  
Sh Wave ◽  
Temporal Separation ◽  
Near Surface ◽  
Near Surface Geophysics

Imaging shallow subsurface voids, such as karsts, sinkholes, pinch-outs, dikes, and man-made voids, is an important task in near-surface geophysics. We have developed a new diffraction-based methodology for void detection and imaging. Due to the low signal-to-noise ratio of the diffracted signal in surface acquisition setups, we advocate the use of an SH-wave multicomponent crosshole acquisition. Naturally, the same setup can be used for velocity model building using tomography and for void imaging. The SH-wave data are migrated using a model-based, image-point-dependent automatic muting function that separates direct arrivals from diffracted events in the migration process. For the purpose of location and velocity analysis, data are migrated to the depth imaging offset domain. Only when the velocity model and imaging locations are correct will the diffracted energy be coherently focused to the void location and the diffracted event moveout in the migrated gather will be flat. We found that the received diffracted signal is clearer and has better temporal separation compared with a conventional P-wave crosshole survey. We determined the usefulness of this method using synthetic and field data examples for 2D acquisitions and a synthetic 3D case, showing that a precise imaging is possible. The importance of the S-waves velocity model, which can be extracted from the same survey using conventional tomography methods, is also discussed.

Reports From the Field: “Vini Ansanm” Come Together for Inclusive Community Music Development in Port-au-Prince, Haiti

2020 ◽  
pp. 273-289
Author(s):  
Donald DeVito ◽  
Gertrude Bien-Aime ◽  
Hannah Ehrli ◽  
Jamie Schumacher
Keyword(s):  
Social Media ◽  
Inclusive Education ◽  
Children With Disabilities ◽  
Small Population ◽  
Significant Loss ◽  
Community Music ◽  
Music Learning ◽  
Loss Of Life

Haiti has experienced a series of catastrophic natural disasters in recent decades, resulting in significant loss of life and long-term damage to infrastructure. One critical outcome of these disasters is that there are approximately 400,000 orphans in the small population of just over 10 million. Throughout Haiti, children with disabilities are often considered cursed, and thus are rejected by the community in which they live. Haitian children with disabilities need creative and educational activities that will help them grow, develop, enjoy their lives, and become accepted members of the community. This chapter on the Haitian Center for Inclusive Education presents a case study of social media engagement and music learning, with an emphasis on social justice that has contributed to sustainable efforts.

scholarly journals Nutrient retention behind a tropical mega-dam: a case study of the Sardar Sarovar Dam, India

2021 ◽  
Vol 3 (1) ◽  
Author(s):  
Harish Gupta ◽  
S. Kiran Kumar Reddy ◽  
Mounika Chiluka ◽  
Vamshikrishna Gandla
Keyword(s):  
Arabian Sea ◽  
Inorganic Nitrogen ◽  
Nutrient Retention ◽  
Significant Loss ◽  
N Removal ◽  
Narmada River ◽  
Sardar Sarovar ◽  
The Impact

AbstractIn this study, we demonstrate the impact of the construction of a mega-dam on the nutrient export regime of a large tropical river into the Arabian Sea. Long-term (11 years) fortnight nutrient parameters, upstream and downstream to Sardar Sarovar (SS) Dam, were examined to determine the periodical change in nutrient fluxes from the Narmada River, India. During this 11-year period, the average discharge of the Narmada River upstream to Rajghat (35.3 km3 year−1) was higher than that of downstream at Garudeshwar (33.9 km3 year−1). However, during the same period, the suspended sediment load was reduced by 21 million tons (MT) from 37.9 MT at Rajghat to 16.7 MT at Garudeshwar. Similarly, mean concentrations of dissolved silica (DSi) reduced from 470 (upstream) to 214 µM (downstream), dissolved inorganic phosphate (DIP) from 0.84 to 0.38 µM, and dissolved inorganic nitrogen (DIN) from 43 to 1.5 µM. It means that about 54%, 55%, and 96% flux of DSi, DIP, and DIN retained behind the dam, respectively. The estimated denitrification rate (80,000 kg N km−2 year−1) for the reservoir is significantly higher than N removal by lentic systems, globally. We hypothesize that processes such as biological uptake and denitrification under anoxic conditions could be a key reason for the significant loss of nutrients, particularly of DIN. Finally, we anticipated that a decline in DIN fluxes (by 1.13 × 109 mol year−1) from the Narmada River to the Arabian Sea might reduce the atmospheric CO2 fixation by 7.46 × 109 mol year−1.

scholarly journals Photonic resonator interferometric scattering microscopy

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Nantao Li ◽  
Taylor D. Canady ◽  
Qinglan Huang ◽  
Xing Wang ◽  
Glenn A. Fried ◽  
...  
Keyword(s):  
Signal To Noise Ratio ◽  
Scattered Light ◽  
Near Field ◽  
Field Enhancement ◽  
Protein Detection ◽  
Significant Loss ◽  
Photonic Band Structure ◽  
Large Intensity ◽  
Photonic Band ◽  
Intensity Contrast

AbstractInterferometric scattering microscopy is increasingly employed in biomedical research owing to its extraordinary capability of detecting nano-objects individually through their intrinsic elastic scattering. To significantly improve the signal-to-noise ratio without increasing illumination intensity, we developed photonic resonator interferometric scattering microscopy (PRISM) in which a dielectric photonic crystal (PC) resonator is utilized as the sample substrate. The scattered light is amplified by the PC through resonant near-field enhancement, which then interferes with the <1% transmitted light to create a large intensity contrast. Importantly, the scattered photons assume the wavevectors delineated by PC’s photonic band structure, resulting in the ability to utilize a non-immersion objective without significant loss at illumination density as low as 25 W cm−2. An analytical model of the scattering process is discussed, followed by demonstration of virus and protein detection. The results showcase the promise of nanophotonic surfaces in the development of resonance-enhanced interferometric microscopies.

Inversion of 3D VSP P‐wave data for local anisotropy: A case study

2003 ◽  
Author(s):  
Petr Jílek ◽  
Brian Hornby ◽  
Amal Ray
Keyword(s):  
P Wave ◽  
Local Anisotropy ◽  
Wave Data

Kinematic interpretation in the prestack depth‐migrated domain

Geophysics ◽  
1997 ◽  
Vol 62 (4) ◽  
pp. 1226-1237 ◽  
Author(s):  
Irina Apostoiu‐Marin ◽  
Andreas Ehinger
Keyword(s):  
Signal To Noise Ratio ◽  
Velocity Model ◽  
Point Of View ◽  
Prestack Depth Migration ◽  
Depth Migration ◽  
Velocity Models ◽  
Time Domain Data ◽  
And Migration ◽  
Point To Point ◽  
Homogeneous Media

Prestack depth migration can be used in the velocity model estimation process if one succeeds in interpreting depth events obtained with erroneous velocity models. The interpretational difficulty arises from the fact that migration with erroneous velocity does not yield the geologically correct reflector geometries and that individual migrated images suffer from poor signal‐to‐noise ratio. Moreover, migrated events may be of considerable complexity and thus hard to identify. In this paper, we examine the influence of wrong velocity models on the output of prestack depth migration in the case of straight reflector and point diffractor data in homogeneous media. To avoid obscuring migration results by artifacts (“smiles”), we use a geometrical technique for modeling and migration yielding a point‐to‐point map from time‐domain data to depth‐domain data. We discover that strong deformation of migrated events may occur even in situations of simple structures and small velocity errors. From a kinematical point of view, we compare the results of common‐shot and common‐offset migration. and we find that common‐offset migration with erroneous velocity models yields less severe image distortion than common‐shot migration. However, for any kind of migration, it is important to use the entire cube of migrated data to consistently interpret in the prestack depth‐migrated domain.

Lithospheric architecture of the Ligurian Basin from seismic travel time tomography

2021 ◽  
Author(s):  
Anke Dannowski ◽  
Heidrun Kopp ◽  
Ingo Grevemeyer ◽  
Grazia Caielli ◽  
Roberto de Franco ◽  
...  
Keyword(s):  
Seismic Data ◽  
Velocity Model ◽  
P Wave ◽  
Central Basin ◽  
Uppermost Mantle ◽  
Mantle Boundary ◽  
Oceanic Spreading ◽  
Refraction Seismic ◽  
Back Arc ◽  
Ligurian Basin

&lt;p&gt;The Ligurian Basin is located north-west of Corsica at the transition from the western Alpine orogen to the Apennine system. The Back-arc basin was generated by the southeast retreat of the Apennines-Calabrian subduction zone. The opening took place from late Oligocene to Miocene. While the extension led to extreme continental thinning little is known about the style of back-arc rifting. Today, seismicity indicates the closure of this back-arc basin. In the basin, earthquake clusters occur in the lower crust and uppermost mantle and are related to re-activated, inverted, normal faults created during rifting.&lt;/p&gt;&lt;p&gt;To shed light on the present day crustal and lithospheric architecture of the Ligurian Basin, active seismic data have been recorded on short period ocean bottom seismometers in the framework of SPP2017 4D-MB, the German component of AlpArray. An amphibious refraction seismic profile was shot across the Ligurian Basin in an E-W direction from the Gulf of Lion to Corsica. The profile comprises 35 OBS and three land stations at Corsica to give a complete image of the continental thinning including the necking zone.&lt;/p&gt;&lt;p&gt;The majority of the refraction seismic data show mantle phases with offsets up to 70 km. The arrivals of seismic phases were picked and used to generate a 2-D P-wave velocity model. The results show a crust-mantle boundary in the central basin at ~12 km depth below sea surface. The P-wave velocities in the crust reach 6.6 km/s at the base. The uppermost mantle shows velocities &gt;7.8 km/s. The crust-mantle boundary becomes shallower from ~18 km to ~12 km depth within 30 km from Corsica towards the basin centre. The velocity model does not reveal an axial valley as expected for oceanic spreading. Further, it is difficult to interpret the seismic data whether the continental lithosphere was thinned until the mantle was exposed to the seafloor. However, an extremely thinned continental crust indicates a long lasting rifting process that possibly did not initiate oceanic spreading before the opening of the Ligurian Basin stopped. The distribution of earthquakes and their fault plane solutions, projected along our seismic velocity model, is in-line with the counter-clockwise opening of the Ligurian Basin.&lt;/p&gt;

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