Facies and Stratigraphic Controls on Velocity Anomalies in The North Madura Platform, Offshore East Java Basin

2018 ◽  
Author(s):  
F. H. Darmawan
Keyword(s):  
The North ◽  
Velocity Anomalies

Role of inherited structures and magmatism in North Tanzania from high resolution teleseismic P and S body-wave tomographies.

2021 ◽  
Author(s):  
Stéphanie Gautier ◽  
Adeline Clutier ◽  
Christel Tiberi ◽  
Fleurice Parat ◽  
Benoit Gibert ◽  
...  
Keyword(s):  
Body Wave ◽  
A Priori ◽  
Regional Scale ◽  
Velocity Model ◽  
S Wave ◽  
Fine Grid ◽  
Local Tomography ◽  
The North ◽  
Velocity Anomalies

<p>The North Tanzanian Divergence (NTD) is a zone of rift initiation. Its surface expression results from interactions between deep-mantle (mantle plume), lithospheric (inherited rheology and stratification, melting...) and crustal (dyke propagation, fault activation...) processes. However, the role of each process on the observed surface activity is still debated, because highly difficult to decorrelate.</p><p>We recently carried out a study to obtain enhanced P and S-wave tomography, from the surface down to 150-200 km depth. The particularity of our method consists in its initial velocity model. It is composed of a 1D IASP91 regional velocity model in which we inserted an a priori 3D crustal velocity model with a fine grid. This crustal model was deduced from an independent local tomography inversion.</p><p>The P and S images obtained, resulting from the teleseismic inversion of this hybrid method, show strong contrasted velocity anomalies: from 10 % of P (Vp) and S velocity (Vs) variation on the craton, to -17 % below the rift axis. The anomalies locations are consistent with the surface geology (rifting basin, border faults, volcanoes). At a regional scale, the strongest velocity contrasts correspond to the lithospheric inherited structure (Tanzanian craton and Proterozoic belts) boundaries, which control the propagation of the rift. In particular, the Masai cratonic block, south of the NTD, is inferred to have a strong influence in the rift evolution. The transition from the North-South axial valley into three diverging rift arms (Eyasi, Natron-Manyara and Pangani) is likely due to the change in rheology and to the presence of magma along inherited sutures between the craton and the mobile belts.</p><p>However, interrogations about the role of the thermal changes, the melt/fluid presence and the mantle composition in the NTD on these velocity anomalies still remain. To distinguish which parameters are acting in the rift, we realize a Vp/Vs ratio map. With this new data, and in the light of parallel petrological studies, we interpret the Vp/Vs anomalies in term of gas and/or melt concentration zones.</p>

scholarly journals Insights from the P Wave Travel Time Tomography in the Upper Mantle Beneath the Central Philippines

2021 ◽  
Vol 13 (13) ◽  
pp. 2449
Author(s):  
Huiyan Shi ◽  
Tonglin Li ◽  
Rui Sun ◽  
Gongbo Zhang ◽  
Rongzhe Zhang ◽  
...  
Keyword(s):  
Travel Time ◽  
Upper Mantle ◽  
High Velocity ◽  
Velocity Structure ◽  
The Philippines ◽  
P Wave ◽  
The South ◽  
Teleseismic Tomography ◽  
The North ◽  
Velocity Anomalies

In this paper, we present a high resolution 3-D tomographic model of the upper mantle obtained from a large number of teleseismic travel time data from the ISC in the central Philippines. There are 2921 teleseismic events and 32,224 useful relative travel time residuals picked to compute the velocity structure in the upper mantle, which was recorded by 87 receivers and satisfied the requirements of teleseismic tomography. Crustal correction was conducted to these data before inversion. The fast-marching method (FMM) and a subspace method were adopted in the forward step and inversion step, respectively. The present tomographic model clearly images steeply subducting high velocity anomalies along the Manila trench in the South China Sea (SCS), which reveals a gradual changing of the subduction angle and a gradual shallowing of the subduction depth from the north to the south. It is speculated that the change in its subduction depth and angle indicates the cessation of the SCS spreading from the north to the south, which also implies that the northern part of the SCS opened earlier than the southern part. Subduction of the Philippine Sea (PS) plate is exhibited between 14° N and 9° N, with its subduction direction changing from westward to eastward near 13° N. In the range of 11° N–9° N, the subduction of the Sulu Sea (SS) lies on the west side of PS plate. It is notable that obvious high velocity anomalies are imaged in the mantle transition zone (MTZ) between 14° N and 9° N, which are identified as the proto-SCS (PSCS) slabs and paleo-Pacific (PP) plate. It extends the location of the paleo-suture of PSCS-PP eastward from Borneo to the Philippines, which should be considered in studying the mechanism of the SCS and the tectonic evolution in SE Asia.

Hotspot signatures at the North American passive margin

Geology ◽  
2020 ◽  
Author(s):  
Zhongmin Tao ◽  
Aibing Li ◽  
Karen M. Fischer
Keyword(s):  
North America ◽  
New England ◽  
Velocity Model ◽  
Passive Margin ◽  
Small Scale ◽  
Low Velocity ◽  
Velocity Anomaly ◽  
The North ◽  
New Information ◽  
Velocity Anomalies

The presence of localized low-velocity anomalies in the upper mantle beneath the passive Atlantic margin in North America is a puzzling geophysical observation. Whether the anomalies are caused by the remnant heat from past hotspots or ongoing asthenospheric upwelling is still debated. We addressed the formation of the anomalies based on a recent velocity model for eastern North America, which reveals new information on their shapes and anisotropic signatures. The low-velocity anomaly in New England appears as a narrow column above 90 km depth and broadens westward at depths of 120–200 km. Two slow anomalies are imaged under the central Appalachian Mountains between 140 km and 240 km. These low velocities correspond to pronounced positive radial anisotropy (Vsh > Vsv), indicating a dominantly horizontal asthenospheric flow. They also coincide with the tracks of the Great Meteor hotspot (140–115 Ma) and an inferred hidden hotspot (60–50 Ma). The anomalies in the central Appalachians could be due to lithospheric interaction with the second hotspot and subsequent lithospheric instabilities. The complex shape of the New England anomaly is consistent with interaction with both hotspots. The first hotspot could have eroded the base of the lithosphere, forming a channel, and the second hotspot could have further thinned the lithosphere and produced a localized cavity at shallow depths. Consequently, the indented lithosphere base would have filled with channelized asthenospheric flow or produced small-scale convection, helping to sustain the slow anomaly. Low-velocity anomalies at the North America passive margin are likely the consequences of prior hotspot interactions.

scholarly journals Interannual Variability of the Altimetry-Derived Eddy Field and Surface Circulation in the Extratropical North Atlantic Ocean in 1993–2001

2005 ◽  
Vol 35 (4) ◽  
pp. 405-426 ◽  
Author(s):  
Denis L. Volkov
Keyword(s):  
Interannual Variability ◽  
North Atlantic ◽  
North Atlantic Ocean ◽  
Labrador Sea ◽  
Geostrophic Velocity ◽  
The North ◽  
Iceland Basin ◽  
Surface Circulation ◽  
Velocity Anomalies ◽  
Generation Mechanisms

Abstract The distribution of surface eddy kinetic energy (EKE) depicts main oceanic surface circulation features. The interannual variability of EKE and associated geostrophic velocity anomalies in the North Atlantic Ocean were analyzed to describe the variations in oceanic currents between 1993 and 2002. The sea level anomaly maps of the combined TOPEX/Poseidon + ERS-1/2 and TOPEX/Poseidon-alone satellite altimetry data were used to derive EKE. The study focused on the areas of the Gulf Stream extension (GS), North Atlantic Current (NAC), Azores Current (AC), and the northeastern (Rockall Channel and Iceland Basin) and northwestern (Irminger Basin and Labrador Sea) North Atlantic. The interannual variability of the altimetry-derived EKE field in the GS extension area reflected the meridional displacements of the GS core described in earlier studies. The interannual change of EKE in the AC was characterized by high values in 1993–95 followed by lower EKE in subsequent years. The interannual variability of EKE in the NAC area west of the Mid-Atlantic Ridge exhibited an out-of-phase change between the band centered at ∼47°N and two bands on either side centered at ∼43° and ∼50°N. In the Rockall Channel the geostrophic velocity anomalies indicated an intensified northeastward flow in 1993–95 followed by a relaxation in 1996–2000. The EKE band associated with the NAC branch in the Iceland Basin was found to be extended farther west after 1996, possibly following the North Atlantic Oscillation (NAO)-induced shift of the subpolar front. A rise of EKE was observed in the Irminger Basin from 1995 to 1999. This rise may have been associated with large anticyclonic geostrophic velocity anomalies, which indicated significant weakening of the cyclonic circulation in the Irminger Basin after 1996, and/or with possibly intensified eddy generation mechanisms due to the NAO-induced approach of the subpolar front. The interannual change of EKE in the Labrador Sea did not appear to always follow the atmospheric forcing expressed by NAO. Therefore other eddy generation mechanisms in the Labrador Sea can be important.

Investor-State Dispute Settlement under NAFTA Chapter 11: The Shape of Things to Come?

1998 ◽  
Vol 35 ◽  
pp. 263-290
Author(s):  
J. Anthony VanDuzer
Keyword(s):  
Free Trade Agreement ◽  
Dispute Settlement ◽  
Trade Agreement ◽  
Minimum Standards ◽  
The North ◽  
State Behaviour ◽  
Nafta Chapter 11 ◽  
To Come ◽  
The Right

SummaryRecently, there has been a proliferation of international agreements imposing minimum standards on states in respect of their treatment of foreign investors and allowing investors to initiate dispute settlement proceedings where a state violates these standards. Of greatest significance to Canada is Chapter 11 of the North American Free Trade Agreement, which provides both standards for state behaviour and the right to initiate binding arbitration. Since 1996, four cases have been brought under Chapter 11. This note describes the Chapter 11 process and suggests some of the issues that may arise as it is increasingly resorted to by investors.

Long-term Cyclic Variations of Prominences, Green and Red Coronae over Solar Cycles

2000 ◽  
Vol 179 ◽  
pp. 201-204
Author(s):  
Vojtech Rušin ◽  
Milan Minarovjech ◽  
Milan Rybanský
Keyword(s):  
Emission Lines ◽  
High Latitudes ◽  
Green Line ◽  
Solar Cycles ◽  
The South ◽  
Coronal Emission ◽  
Local Maxima ◽  
The North ◽  
Cyclic Variations

AbstractLong-term cyclic variations in the distribution of prominences and intensities of green (530.3 nm) and red (637.4 nm) coronal emission lines over solar cycles 18–23 are presented. Polar prominence branches will reach the poles at different epochs in cycle 23: the north branch at the beginning in 2002 and the south branch a year later (2003), respectively. The local maxima of intensities in the green line show both poleward- and equatorward-migrating branches. The poleward branches will reach the poles around cycle maxima like prominences, while the equatorward branches show a duration of 18 years and will end in cycle minima (2007). The red corona shows mostly equatorward branches. The possibility that these branches begin to develop at high latitudes in the preceding cycles cannot be excluded.

An ultrastructural study of sertoli cells in two geographically isolated populations of Aphanius dispar

1992 ◽  
Vol 50 (1) ◽  
pp. 548-549
Author(s):  
Taber A. Ba-Omar ◽  
Philip F. Prentis
Keyword(s):  
Ultrastructural Level ◽  
Uranyl Acetate ◽  
Freshwater Teleost ◽  
Isolated Populations ◽  
En Bloc ◽  
The North ◽  
Group A ◽  
Ultrathin Sections ◽  
Group B ◽  
Geographically Isolated

We have recently carried out a study of spermiogenic differentiation in two geographically isolated populations of Aphanius dispar (freshwater teleost), with a view to ascertaining variation at the ultrastructural level. The sampling areas were the Jebel Al Akhdar in the north (Group A) and the Dhofar region (Group B) in the south. Specimens from each group were collected, the testes removed, fixed in Karnovsky solution, post fixed in OsO, en bloc stained with uranyl acetate and then routinely processed to Agar 100 resin, semi and ultrathin sections were prepared for study.

SEM and TEM observations of sperm development in the testis of the freshwater fish Oreochromis mossambicus

1990 ◽  
Vol 48 (3) ◽  
pp. 58-59
Author(s):  
Daryl A. Cornish ◽  
George L. Smit
Keyword(s):  
Morphological Characteristics ◽  
Oreochromis Mossambicus ◽  
Breeding Cycle ◽  
Limited Information ◽  
North West ◽  
The North ◽  
Sem And Tem ◽  
Sperm Development ◽  
Ultrastructural Characteristics ◽  
The University

Oreochromis mossambicus is currently receiving much attention as a candidater species for aquaculture programs within Southern Africa. This has stimulated interest in its breeding cycle as well as the morphological characteristics of the gonads. Limited information is available on SEM and TEM observations of the male gonads. It is known that the testis of O. mossambicus is a paired, intra-abdominal structure of the lobular type, although further details of its characteristics are not known. Current investigations have shown that spermatids reach full maturity some two months after the female becomes gravid. Throughout the year, the testes contain spermatids at various stages of development although spermiogenesis appears to be maximal during November when spawning occurs. This paper describes the morphological and ultrastructural characteristics of the testes and spermatids.Specimens of this fish were collected at Syferkuil Dam, 8 km north- west of the University of the North over a twelve month period, sacrificed and the testes excised.

Skeletochronology and mark–recapture assessments of growth in the North African agamid lizard (Agama impalearis)

1999 ◽  
Vol 249 (4) ◽  
pp. 455-461
Author(s):  
El Hassan El Mouden ◽  
Mohammed Znari ◽  
Richard P. Brown
Keyword(s):  
North African ◽  
Mark Recapture ◽  
Agamid Lizard ◽  
The North
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