Submarine canyons: Velocity replacement by wave‐equation datuming before stack

Geophysics ◽  
1986 ◽  
Vol 51 (8) ◽  
pp. 1572-1579 ◽  
Author(s):  
John R. Berryhill
Keyword(s):  
Wave Equation ◽  
Sea Water ◽  
Original Data ◽  
Acoustic Velocity ◽  
Computational Method ◽  
Common Source ◽  
Submarine Canyons ◽  
Sea Floor ◽  
Exposed Rock ◽  
Corrected Data

Submarine canyons incised into the continental slope interfere with the quality of common‐midpoint (CMP) stacked seismic data obtainable from reflectors beneath the sea floor. The interference problem is caused by rough topography in conjunction with the contrast between the acoustic velocity of sea water and the velocity of the exposed rock layers. Geophysicists have long recognized that part of the solution is to replace the traveltimes of raypaths through the water by their traveltimes through an identical thickness of rock. However, use of wave‐equation datuming to effect velocity replacement yields an additional correction for the change in raypath direction that occurs in crossing from rock to sea water; the wave‐equation datuming implementation of velocity replacement is more comprehensive and complete. The wave‐equation datuming method requires an accurate sea‐floor profile as part of the input, along with values of replacement velocity; it does not require knowledge of geology or velocities at depths much greater than the sea floor. Unstacked common‐source and common‐receiver records are processed to appear as if sources and receivers were moved to the water bottom; the velocity of water is replaced; and the sources and receivers are moved back to the sea surface through the replacement medium. The computational method is well‐suited to the irregular surfaces and laterally variable velocities inherent in the problem of submarine canyons. The advantage of this method is that the corrected seismic records accurately emulate the data that would actually be observed if the acoustic velocity of water could be changed physically. The normal‐moveout (NMO) velocity for optimum CMP stacking becomes the root mean square of the layer velocities, including the velocity substituted for that of water. The spurious lateral variation of stacking velocity in the original data is eliminated. Processing of the corrected data through velocity analysis, stacking, migration, and conversion to depth is therefore more reliable.

Deep‐water peg legs and multiples: Emulation and suppression

Geophysics ◽  
1986 ◽  
Vol 51 (12) ◽  
pp. 2177-2184 ◽  
Author(s):  
J. R. Berryhill ◽  
Y. C. Kim
Keyword(s):  
Wave Equation ◽  
Seismic Data ◽  
Water Layer ◽  
Original Data ◽  
Equation Method ◽  
Multiple Reflections ◽  
Step Method ◽  
Arrival Times ◽  
Sea Floor ◽  
Water Bottom

This paper discusses a two‐step method for predicting and attenuating multiple and peg‐leg reflections in unstacked seismic data. In the first step, an (observed) seismic record is extrapolated through a round‐trip traversal of the water layer, thus creating an accurate prediction of all possible multiples. In the second step, the record containing the predicted multiples is compared with and subtracted from the original. The wave‐equation method employed to predict the multiples takes accurate account of sea‐floor topography and so requires a precise water‐bottom profile as part of the input. Information about the subsurface below the sea floor is not required. The arrival times of multiple reflections are reproduced precisely, although the amplitudes are not accurate, and the sea floor is treated as a perfect reflector. The comparison step detects the similarities between the computed multiples and the original data, and estimates a transfer function to equalize the amplitudes and account for any change in waveform caused by the sea‐floor reflector. This two‐step wave‐equation method is effective even for dipping sea floors and dipping subsurface reflectors. It does not depend upon any assumed periodicity in the data or upon any difference in stacking velocity between primaries and multiples. Thus it is complementary to the less specialized methods of multiple suppression.

THE POLITICAL ORIGINS OF ISLAMIC COURTS IN DIVIDED SOCIETIES: THE CASE OF MALAYSIA

2018 ◽  
Vol 33 (2) ◽  
pp. 248-270 ◽  
Author(s):  
Kikue Hamayotsu
Keyword(s):  
Institutional Development ◽  
Original Data ◽  
Religious Communities ◽  
Common Source ◽  
Institutional Power ◽  
Semistructured Interviews ◽  
Reform Period ◽  
Institutional Expansion ◽  
Critical Phases ◽  
Islamic Courts

AbstractThe way in which Islamic courts and laws are developed and how religious legal apparatuses shape the relations between—and within—religious communities has been a common source of debate among scholars. This article analyzes the growing institutional power and authority of Islamic courts and judges in Malaysia since the late 1980s to contribute to this theoretical debate. Specifically, it compares two critical phases of institutional development of Islamic courts in Malaysia's largely secular judicial system: the first under the premiership of Mahathir Mohamad before the dismissal of his deputy, Anwar Ibrahim (1980–1998), and the second under the post-reformasi (reform) period (1999–present). Original data gathered at the Jabatan Kehakiman Syariah Malaysia (Department of Syariah Judiciary Malaysia) and other government and legal agencies, fieldwork, and semistructured interviews with Islamic and civil court officials both at the federal and state levels document the institutional expansion and administrative independence that the Islamic courts and judges have successively gained in relation to their civil counterparts. It is argued that the gradual bureaucratization of Islamic courts can best be explained with reference to the interests—and strategic coalitions—of political and religious elites within the majority community to sustain a dominant regime and majoritarian rule based on communal identity.

scholarly journals The Formation and Composition of the Gas Content of Sea Ice

1979 ◽  
Vol 22 (86) ◽  
pp. 67-81 ◽  
Author(s):  
V. L. Tsurikov
Keyword(s):  
Sea Ice ◽  
Sea Water ◽  
Major Effect ◽  
Relative Volume ◽  
Gas Content ◽  
Dominant Factor ◽  
Sea Floor ◽  
Sea Bottom ◽  
Initial Freezing ◽  
Air Pockets

Abstract The different factors contributing to the formation of the gas porosity of sea ice are: (Ia) gases captured during the formation of the initial ice cover, (Ib) gases released from solution during the initial freezing of sea-water, (Ic) the inclusion of gases rising from the sea bottom, (2a) the substitution of gas for brine drained from the ice during times of melting, (2b) the release of gas from the brine within the ice during the course of partial freezing, and (2c) the formation of voids filled with water vapour during the course of internal melting. An analysis is made of each of these processes and it is concluded that processes Ib, 2a, and 2C are important. Process Ic may also be a major effect but it is difficult to evaluate until the rate of gas release from the sea floor is better known. The migration of air pockets into the ice from the overlying snow is shown to be a possible but not a significant effect. Available data on the composition of gas in sea ice are reviewed and it is shown to be significantly different from air. Possible causes for these differences are discussed. The porosity of sea ice, i.e. the total relative volume of its gas plus its brine inclusions, is one of the factors strongly affecting its strength, as has been shown by Tsurikov (1947) and by Weeks and Assur (1968). In seas with high salinities the effect of the presence of brine within the ice will usually be the dominant factor. However on water bodies with low salinities the effect of the gas included within the ice may be greater than the effect of the brine. Despite its significance there have not been any attempts at a quantitative analysis of the entrapment of gas in sea ice. This paper is an attempt at such a study.

Note on Cohen's Kappa

1989 ◽  
Vol 65 (1) ◽  
pp. 223-226 ◽  
Author(s):  
Tarald O. Kvålseth
Keyword(s):  
Computational Procedure ◽  
Original Data ◽  
Computational Method ◽  
Distance Metrics ◽  
Cohen’S Kappa ◽  
Data Table ◽  
Cohen's Kappa ◽  
Hypothetical Data ◽  
Agreement Measure

Cohen's Kappa is a measure of the over-all agreement between two raters classifying items into a given set of categories. This communication describes a simple computational method of determining the agreement on specific categories without the need to collapse the original data table as required by the previous Kappa-based method. It is also pointed out that Kappa may be formulated in terms of certain distance metrics. The computational procedure for the specific agreement measure is exemplified using hypothetical data from psychological diagnoses.

Generation of metal deposits on the sea floor

1976 ◽  
Vol 13 (1) ◽  
pp. 126-135 ◽  
Author(s):  
B. J. Fryer ◽  
R. W. Hutchinson
Keyword(s):  
Sea Water ◽  
Metal Sulfide ◽  
Base Metals ◽  
Base Metal Sulfide ◽  
Gold Ores ◽  
Sulfide Deposits ◽  
Sea Floor ◽  
Metalliferous Sediments ◽  
Sea Bottom ◽  
Metal Abundances

Recent studies of volcanogenic base metal sulfide deposits and of metalliferous sediments in the Red Sea indicate precipitation of iron and base metals under conditions varying from reducing to oxidizing, at or near sites of fumarolic brine emission onto the sea floor. Differing lithofacies of iron-rich sediments were apparently deposited penecontemporaneously, mainly in response to changing chemical, biological, and sedimentary lithofacies conditions.Iron-rich sediments associated with the cupriferous pyrite bodies of Cyprus have been studied to determine the behavior of Fe, Mn, Cu, Zn, Pb, Ni, Co, Cr, Sn, Mo, Ag, and Au, when these fumarolic brines enter the sea bottom environment. Variations in metal abundances and ratios indicate that rapidly changing Eh is a major factor controlling metal deposition on the sea floor. The Fe/Mn ratio in these sediments is a useful indicator of the amount of interaction of these fumarolic brines and normal oxygenated sea water. Results suggest that zinc, copper, and gold are concentrated in the high Fe/Mn ratio proximal sediments; nickel is concentrated in the low Fe/Mn ratio distal sediments; and lead, silver, tin, and molybdenum are relatively unaffected by oxidation of the fumarolic brine solution by normal sea water.These concepts of sea floor deposition controlling the distribution of metals may also be applicable to other types of stratabound metalliferous deposits, like certain skarn, greisen, and gold ores, heretofore considered to be of epigenetic origin.

MIDDLE DEVONIAN SALT FORMATIONS AND THEIR BROMIDE CONTENT, ELK POINT AREA, ALBERTA

1966 ◽  
Vol 3 (3) ◽  
pp. 263-275 ◽  
Author(s):  
N. C. Wardlaw ◽  
D. W. Watson
Keyword(s):  
Fresh Water ◽  
Surface Runoff ◽  
Middle Devonian ◽  
Sea Water ◽  
Weight Percent ◽  
Downward Movement ◽  
Sea Floor ◽  
Surface Evaporation ◽  
Crystallization Solution ◽  
Cold Lake

The Prairie Evaporite formation, or First Salt, of the Elk Point area contains three types of halite: chevron, clear, and brown. The chevron halite is thought to be primary and to have grown upwards from the Devonian sea floor. The origin of the clear and brown varieties is not known. Where these types occur together, the clear halite has a tendency to contain more bromide than either chevron halite or brown halite. The total range for bromide in halite from the Prairie Evaporite is from 0.004 to 0.02 weight percent (wt.%).The Cold Lake and Lotsberg formations, the lower two salts, consist of clear halite which is so low in bromide (0.0004 wt.%) that it could not have crystallized from sea water, neither could this halite have crystallized from sea water previously saturated by dissolving halite. It is probable that the lower two salts resulted from solution of halite in fresh water, with subsequent crystallization. Solution may have occurred during discharge of meteoric groundwater, while the basin was structurally low, subsequent surface evaporation having promoted crystallization. In this way, salt could have been recycled without removal from the area. Alternatively, surface runoff, and downward movement of surface runoff, may have been important in the recycling of halite.Groundwater in Devonian formations of central Alberta, and spring waters from Devonian formations in Manitoba, are saline and relatively high in bromide (0.001–0.10 wt.% Br). The bromide content cannot be explained simply by solution of halite in meteoric waters. Either these brines are modified remnants of seawater, or else there is some undefined source of bromine causing enrichment.

Multicomponent ocean bottom and vertical cable seismic acquisition for wavefield reconstruction

Geophysics ◽  
2010 ◽  
Vol 75 (6) ◽  
pp. WB87-WB94 ◽  
Author(s):  
Lasse Amundsen ◽  
Harald Westerdahl ◽  
Mark Thompson ◽  
Jon Andre Haugen ◽  
Arne Reitan ◽  
...  
Keyword(s):  
Wave Equation ◽  
Particle Velocity ◽  
Pressure Field ◽  
Vertical Component ◽  
Ocean Bottom ◽  
Sea Floor ◽  
Number Of Components ◽  
Shot Point ◽  
Seismic Acquisition ◽  
Wavefield Decomposition

In ocean-bottom seismic and vertical-cable surveying, receiver stations are stationary on the sea floor while a source vessel shoots on a predetermined [Formula: see text] grid on the sea surface. To reduce exploration cost, the shot point interval often is so coarse that the data recorded at a given receiver station are undersampled and thus irrecoverably aliased. However, when the pressure field and its [Formula: see text]- and [Formula: see text]-derivatives are measured in the water column, the nonaliased pressure field can be reconstructed by interpolation. Likewise, if the vertical component of the particle velocity (or acceleration) and its [Formula: see text]- and [Formula: see text]-derivatives are measured, then this component can also be reconstructed by interpolation. The interpolation scheme can be any scheme that reconstructs the field from its sampled values and sampled derivatives. In the case that the two fields’ first-order derivatives are recorded, the total number of components is six. When also their second-order derivatives are measured, the number of components is 10. The properly interpolated measurements of pressure and vertical component of particle velocity from the multicomponent measurements allow true 3D up/down wavefield decomposition (deghosting) and wave-equation demultiple before wave-equation migration.

Palladium, iridium, and gold contents of mafic and ultramafic rocks drilled from the Mid-Atlantic Ridge, Leg 37, Deep Sea Drilling Project

1977 ◽  
Vol 14 (4) ◽  
pp. 777-784 ◽  
Author(s):  
James H. Crocket ◽  
Yuko Teruta
Keyword(s):  
Noble Metals ◽  
Sea Water ◽  
Local Heating ◽  
Ultramafic Rocks ◽  
Gold Content ◽  
Secondary Alteration ◽  
Sea Floor ◽  
Mid Atlantic Ridge ◽  
Weak Trend ◽  
Drilling Project

Basalts and ultramafic rocks from holes 332B and 334 of Leg 37, DSDP, were analyzed for palladium, iridium, and gold by neutron activation. Averages obtained for the basalts are: Pd < 0.69 ppb, Ir < 0.025 ppb, and Au = 2.9 ppb. The samples include one representative of each of the main basaltic lithological units except for Unit III, hole 332B, which is represented by a suite of 14 samples. Averages of 43, 0.60, and 16 ppb were obtained for Pd, Ir, and Au respectively in two ultramafic rocks and a gabbro from hole 334.In comparison with basalts from mid-ocean islands such as Hawaii, Leg 37 sea-floor basalts are significantly depleted in Ir and Pd, but are similar in gold content. These differences may be related to differing degrees of alteration sustained by rocks from these differing environments.The depth profiles for Ir and Pd in hole 332B show no significant trends, but a weak trend of increasing gold content with depth is suggested. Variation of Ir and Pd in adjacent lithological units may be as great as a factor of 50. The Pd distribution in 14 samples from Unit III suggests that these differences probably reflect real differences in average metal content rather than sampling effects. Although alteration of Leg 37 basalts is weak, the low Pd and Ir contents and the variability from flow to flow suggest that reaction with sea water has leached Pd and Ir from these rocks. A possible complementary enhancement of some noble metals including Pd has been noted in the sediments immediately overlying mid-ocean rises. Although gold does not seem to be depleted in Leg 37 basalts there is evidence that the metal is easily mobilized by local heating accompanying igneous intrusive rocks.The average Au/Ir ratio of the Leg 37 basalts is four times higher than that of the ultramafic–mafic rocks of hole 334. Although part of this effect is probably due to secondary alteration, it is considered unlikely that the Leg 37 basalts and ultramafic rocks are petrogenetically related.

RAPID COMMUNICATION Evolutionary response by bivalves to changing Phanerozoic sea-water chemistry

1997 ◽  
Vol 134 (3) ◽  
pp. 403-407 ◽  
Author(s):  
E. M. HARPER ◽  
T. J. PALMER ◽  
J. R. ALPHEY
Keyword(s):  
Water Chemistry ◽  
Sea Water ◽  
Outer Shell ◽  
Sea Floor ◽  
Rapid Communication ◽  
First Case ◽  
Evolutionary Response ◽  
Dynamic Link

Sedimentological evidence suggests that sea-water chemistry has oscillated between ‘Aragonite’ and ‘Calcite’ seas during the course of Phanerozoic time. During ‘Calcite’ sea periods aragonite was soluble and dissolved on the sea-floor. Here we propose, using a survey of familial diversity, that during times of such corrosive seas bivalved molluscs which secreted their shells entirely of aragonite were at a selective disadvantage compared to those with calcitic outer shell layers. This is the first case in which it has been suggested that there was a dynamic link between sea-water chemistry and the evolution of a particular taxon throughout Phanerozoic time.

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