scholarly journals Seismic stratigraphy of the Klints Bank east of Gotland (Baltic Sea): a giant drumlin sealing thermogenic hydrocarbons

2021 ◽  
Vol 41 (1) ◽  
Author(s):  
Wiebke Schäfer ◽  
Christian Hübscher ◽  
Daniel Sopher
Keyword(s):  
Seismic Velocity ◽  
Flow Direction ◽  
Seismic Profiles ◽  
Glacial Origin ◽  
Thrust Faulting ◽  
Seismic Image ◽  
Collapse Structures ◽  
Glaciogenic Sediments ◽  
Deformation Patterns ◽  
Weichselian Glaciation

AbstractThis work analyses six high-resolution multi-channel seismic profiles across the Klints Bank east of Gotland. The Klints Bank consists of a drop-shaped increase of the Quaternary thickness and is oriented in an approximately north-southern direction with a length of over 50 km, a width of about 15 km and a maximum thickness of 150 m. The glacial origin of the Klints Bank can be verified with the dataset presented in this study. We classify the feature as a (giant) drumlin due to its steep up-ice and tapered down-ice face in combination with an orientation parallel to the ice-flow direction of the Weichselian glaciation. The seismic image of the internal structure of the Quaternary unit shows no uniform stratification or deformation patterns; instead, local sub-parallel reflection patterns interlayered with transparent units are observed. The averaged seismic velocity of this unit is about 2000 m/s, which is interpreted as an autochthonous deposition of glaciogenic sediments. Signs of overprinting are interpreted based on the geometry of the flanks of the structure, which appear mostly in the form of collapse structures and lifted blocks due to compressional thrust faulting. Phase-reversed events within and beneath the Quaternary are perceived as strong evidence of fluid (hydrocarbon) presence within the Klints Bank. Organically enriched Palaeozoic shales in south-easterly direction of the Klints Bank presumably give the origin of these thermogenic hydrocarbons.

On Offset Placement of a Compound Droplet in a Channel Flow

2021 ◽  
Author(s):  
Jagannath Mahato ◽  
Dhananjay Kumar Srivastava ◽  
Dinesh Kumar Chandraker ◽  
Rajaram Lakkaraju
Keyword(s):  
Viscosity Ratio ◽  
Stokes Equations ◽  
Temporal Dynamics ◽  
Flow Direction ◽  
Navier Stokes ◽  
Volume Of Fluid Method ◽  
Lateral Migration ◽  
Navier Stokes Equations ◽  
Deformation Patterns ◽  
Compound Droplet

Abstract Investigations on flow dynamics of a compound droplet have been carried out in a two-dimensional fully-developed Poiseuille flow by solving the Navier-Stokes equations with the evolution of the droplet using the volume of fluid method with interface compression. The outer droplet undergoes elongation similar to a simple droplet of same size placed under similar ambient condition in the flow direction, but, the inner droplet evolves in compressed form. The compound droplet is varied starting from the centerline towards the walls of the channel. The simulations showed that on applying an offset, asymmetric slipper-like shapes are observed as opposed to symmetric bullet-like shapes through the centerline. Temporal dynamics, deformation patterns, and droplet shell pinch-off mode vary with the offset, with induction of lateral migration. Also, investigations are done on the effect of various parameters like droplet size, Capillary number, and viscosity ratio on the deformation magnitude and lateral migration.

The extent of middle Pleistocene ice cap in the coastal Dinaric Mountains of Croatia

2016 ◽  
Vol 85 (3) ◽  
pp. 445-455 ◽  
Author(s):  
Tihomir Marjanac ◽  
Ljerka Marjanac
Keyword(s):  
Adriatic Sea ◽  
Middle Pleistocene ◽  
Northern Adriatic Sea ◽  
Northern Adriatic ◽  
Soil Corrosion ◽  
Glacial Origin ◽  
Ice Cap ◽  
Depositional Processes ◽  
Dinaric Mountains ◽  
Glaciogenic Sediments

Solitary limestone blocks and groups of blocks occur on Risnjak and Velebit Mountains and on the northern Adriatic islands of Krk and Rab. Previous researchers have interpreted some of these as a) erratic blocks, b) corrosional remnants, or c) rockfalls. We have studied their mode of occurrence and composition, and revised previous interpretations of their origin in the light of transport mechanism and depositional processes. After analyzing the context of the block positions and the physical processes responsible for their emplacement, and taking into account their sedimentological context (their association with glaciogenic sediments), we herein propose a glacial origin for most of these blocks. However, some blocks are indeed shaped by sub-soil corrosion, as evidenced by their structure. The interpreted erratic blocks on the inner northern Adriatic Sea islands document the presence of middle Pleistocene glaciation of Dinaric Mountains though not its maximal extent, which is still unclear as the ice terminus was in the area that is inundated by postglacial rise of Adriatic Sea. The reconstructed ice cap area, which extended along the coastal mountains from Risnjak Mt. to south Velebit Mt. and across the range from Lika Polje to Rab Island, is conservatively estimated to be 5400 km2.

Seismic velocity precursors to the 2016 Mw 6.5 Norcia (Italy) earthquake

Geology ◽  
2020 ◽  
Vol 48 (9) ◽  
pp. 924-928 ◽  
Author(s):  
C. Chiarabba ◽  
P. De Gori ◽  
M. Segou ◽  
M. Cattaneo
Keyword(s):  
Seismic Velocity ◽  
Time Windows ◽  
Central Italy ◽  
Active Faults ◽  
Central Italy Earthquake ◽  
Preparatory Phase ◽  
Triggering Mechanisms ◽  
Failure Conditions ◽  
Deformation Patterns

Abstract Earthquakes occur as the result of long-term strain accumulation on active faults and complex transient triggering mechanisms. Although laboratory experiments show accelerating deformation patterns before failure conditions are met, imaging similar preparatory phases in nature remains difficult because it requires dense monitoring in advance. The 2016 Amatrice-Visso-Norcia (central Italy) earthquake cascade, captured by an unprecedented seismic network, provided a unique testing ground to image the preparatory phase of a large event. The crustal volume of the Norcia incipient fault was densely illuminated by seismic rays from more than 13,000 earthquakes that occurred within the 3 mo before the main shock nucleation. We performed seismic tomography in distinct time windows that revealed the precursory changes of elastic wave speed, signaling (1) the final locked state of the fault, and (2) the rapid fault-stiffness alterations near the hypocenter just a few weeks before the event. The results are the first instance where short-lived, hard-to-catch crustal properties shed light on evolving earthquake cascades.

Marcellus fracture characterization using P-wave azimuthal velocity attributes: Comparison with production and outcrop data

2015 ◽  
Vol 3 (3) ◽  
pp. SU1-SU15 ◽  
Author(s):  
Tanya L. Inks ◽  
Terry Engelder ◽  
Edward Jenner ◽  
Bruce Golob ◽  
Jacki S. Hocum ◽  
...  
Keyword(s):  
Seismic Velocity ◽  
Marcellus Shale ◽  
Azimuthal Velocity ◽  
P Wave ◽  
Published Data ◽  
Seismic Profiles ◽  
Fracture Characterization ◽  
Decline Curve ◽  
Fracture Models ◽  
Well Data

Analysis of two 3D surveys, available well data, published outcrop data and subsurface information, as well as production data available from the state of Pennsylvania, demonstrates that wide-azimuth seismic is sensitive to variations in fracturing at the scale of individual pads or even individual wells. These variations in fracturing begin to explain why production varies significantly, even locally, within the Marcellus Shale gas play. Rose diagrams from quantitative fracture analysis using azimuthal seismic velocity volumes were compared with published data from Appalachian black shale outcrops and subsurface fracture models proposed in various papers to validate the results from subsurface data. These analyses provided insight into the rock fabric and the presence of systematic joints that likely affect production. There was a strong correlation between the low anisotropy and low heterogeneity of anisotropy and high estimated ultimate recovery (EUR). Additionally, interpreted fracture trend azimuths differed between areas of larger gas EUR and areas of smaller gas EUR as defined by decline curve analysis. Some perforations were likely to perform much better than others along the borehole, based on observed heterogeneity in the seismic profiles and map view.

scholarly journals Englacial seismic reflectivity: imaging crystal-orientation fabric in West Antarctica

2011 ◽  
Vol 57 (204) ◽  
pp. 639-650 ◽  
Author(s):  
Huw J. Horgan ◽  
Sridhar Anandakrishnan ◽  
Richard B. Alley ◽  
Peter G. Burkett ◽  
Leo E. Peters
Keyword(s):  
Crystal Orientation ◽  
Seismic Velocity ◽  
Current Knowledge ◽  
Flow Direction ◽  
Ice Sheet ◽  
West Antarctica ◽  
Amplitude Analysis ◽  
Abrupt Changes ◽  
Seismic Reflectivity ◽  
Ice Sheet Dynamics

AbstractAbrupt changes in crystal-orientation fabric (COF), and therefore viscosity, are observed near the base of the ice sheet throughout West Antarctica. We report on active-source seismic observations from WAIS Divide, mid-stream and downstream on Thwaites Glacier, and the onset region of Bindschadler Ice Stream. These data reveal a prevalence of englacial seismic reflectivity in the bottom quarter of the ice sheet. The observed seismic reflectivity is complex but largely bed-conformable, with long-spatial-wavelength features observed in the flow direction and short-wavelength features observed across flow. A correspondence of englacial structures with bed features is also observed. We determine the origin of the reflectivity to be abrupt changes in the COF of ice, based on the following: (1) observations of englacial reflectivity are consistent with current knowledge of COF within ice sheets, (2) englacial reflectivity caused by COF contrasts requires the simplest genesis, especially at ice divides, and (3) amplitude analysis shows that the observed englacial reflectivity can be explained by contrasts in seismic velocity due to COF changes. We note that the downstream increase in the quantity and complexity of observations indicates that direct observations of COF at ice divides likely underestimate the role that fabric plays in ice-sheet dynamics.

Analysis of the seismic image for the Carpathians and their basement resulting from the reprocessing of 2D seismic profiles

Nafta-Gaz ◽  
2018 ◽  
Vol 74 (8) ◽  
pp. 563-574 ◽  
Author(s):  
Andrzej Urbaniec ◽  
◽  
Łukasz Bajewski ◽  
Robert Bartoń ◽  
Aleksander Wilk ◽  
...  
Keyword(s):  
Seismic Profiles ◽  
The Carpathians ◽  
Seismic Image

Applications of geophysical techniques in permafrost regions

1977 ◽  
Vol 14 (1) ◽  
pp. 117-127 ◽  
Author(s):  
W. J. Scott ◽  
J. A. Hunter
Keyword(s):  
Seismic Velocity ◽  
Seismic Refraction ◽  
Beaufort Sea ◽  
Test Site ◽  
The Arctic ◽  
Seismic Profiles ◽  
Refraction Seismic ◽  
Lake Bottom ◽  
Ice Content ◽  
The Hill

This paper reports the results of some recent geophysical experiments carried out in the Arctic with a variety of methods. In the Beaufort Sea, seismic refraction profiles obtained with both source and receivers on the seabottom indicate the presence of discontinuous near-bottom high-velocity (4200 m/s) material interpreted to be presently aggrading permafrost. Spring-time resistivity soundings taken through the ice in Kugmallit Bay, Beaufort Sea, show the top of permafrost at about 50 m below the bottom. Even for 5-km spreads, the base of permafrost was not observed.Off the southeast coast of Melville Island, refraction seismic profiles shot on the seabottom and resistivity soundings made through summer ice yielded data which correlate with known sub-bottom geology, but which gave no clear indication of either presence or absence of permafrost.Seismic and resistivity measurements made at a number of control sites in the Arctic Islands yielded typical velocities of 3500 m/s and resistivities of 1 × 106 ohm-m for ice-saturated sands. Some correlation was observed between seismic velocity and moisture contents in the range from 10% to 40%.Seismic and resistivity results in IOL Lake at the Involuted Hill test site, Tuktoyaktuk Peninsula, suggest the absence of permafrost under some parts of the lake bottom. On the hill itself, seismic up-hole shooting and VLF resistivity profiling give interpretations of ice distribution which correlate well with drill control. Gamma-gamma logs taken in some of the drill holes correlate well with ice content logged during drilling.

scholarly journals Thrust tectonics in the central part of the External Hellenides, the case of the Gavrovo thrust

2017 ◽  
Vol 47 (2) ◽  
pp. 540
Author(s):  
E. Kamberis ◽  
S. Sotiropoulos ◽  
F. Marnelis ◽  
N. Rigakis
Keyword(s):  
Structural Deformation ◽  
Thrust Belt ◽  
Seismic Profiles ◽  
The West ◽  
Thrust Faulting ◽  
Fold And Thrust Belt ◽  
Thrust Tectonics ◽  
Extensional Faulting ◽  
Surface Geology ◽  
Flat Geometry

Thrust faulting plays an important role in the structural deformation of Gavrovo and Ionian zones in the central part of the ‘External Hellenides’ fold-and-thrust belt. The Skolis mountain in NW Peloponnese as well as the Varassova and Klokova mountains in Etoloakarnania are representative cases of ramp anticlines associated with the Gavrovo thrust. Surface geology, stratigraphic data and interpretation of seismic profiles indicate that it is a crustal-scale thrust acted throughout the Oligocene time. It is characterized by a ramp-flat geometry and significant displacement (greater than 10 km). Out of sequence thrust segmentation is inferred in south Etoloakarnania area. Down flexure and extensional faulting in the Ionian zone facilitated the thrust propagation to the west. The thrust emplacement triggered halokenetic movement of the Triassic evaporites in the Ionian zone as well as diapirisms that were developed in a later stage in the vicinity of the Skolis mountain.

Integrated seismic and electromagnetic model building applied to improve subbasalt depth imaging in the Faroe-Shetland Basin

Geophysics ◽  
2016 ◽  
Vol 81 (1) ◽  
pp. E57-E68 ◽  
Author(s):  
Martin Panzner ◽  
Jan Petter Morten ◽  
Wiktor Waldemar Weibull ◽  
Børge Arntsen
Keyword(s):  
Seismic Data ◽  
Model Building ◽  
Velocity Structure ◽  
Seismic Velocity ◽  
Real Data ◽  
Magnetotelluric Data ◽  
Electromagnetic Data ◽  
Data Inversion ◽  
Seismic Image ◽  
Imaging Results

Subbasalt imaging has gained significant interest in the last two decades, driven by the urge to better understand the geologic structures beneath volcanic layers, which can be up to several kilometers thick. This understanding is crucial for the development and risking of hydrocarbon play models in these areas. However, imaging based on the reflection seismic data alone suffers from severe amplitude transmission losses and interbed multiples in the volcanic sequence, as well as from poor definition of the subbasalt velocity structure. We have considered a sequential imaging workflow, in which the resistivity model from joint controlled-source electromagnetic and magnetotelluric data inversion was used to update the velocity model and to improve the structural definition in the migrated seismic image. The quantitative link between resistivity and velocity was derived from well data. The workflow used standard procedures for seismic velocity analysis, electromagnetic data inversion, and well analysis, and thereby allowed detail control and input based on additional geophysical knowledge and experience in each domain. Using real data sets from the Faroe-Shetland Basin, we can demonstrate that the integration of seismic and electromagnetic data significantly improved the imaging of geologic structures covered by up to several-kilometer-thick extended volcanic sequences. The improved results might alter the interpretation compared with the imaging results from seismic data alone.

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