| 1. |
- Drouin, Vincent, et al.
(författare)
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Crustal movements at a divergent plate boundary: interplay between volcano deformation, geothermal processes, and plate spreading in the Northern Volcanic Zone, Iceland since 2008.
- 2014
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Ingår i: Geophysical Research Abstracts, EGU General Assembly, 27 April–02 May, 2014, Vienna, Austria. ; 16(EGU2014-10740-3)
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)
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| 2. |
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| 3. |
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| 4. |
- Islam, Md. Tariqul, 1980, et al.
(författare)
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Continuous subsidence in the Thingvellir rift graben, Iceland: Geodetic observations since 1967 compared to rheological models of plate spreading
- 2016
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Ingår i: Journal of Geophysical Research - Solid Earth. - 0148-0227 .- 2156-2202. ; 121:1, s. 321-338
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Tidskriftsartikel (refereegranskat)abstract
- North America-Eurasia relative plate motion across the Mid-Atlantic Ridge in south Iceland is partitioned between overlapping ridge segments, the Western Volcanic Zone (WVZ) and the Eastern Volcanic Zone. The Thingvellir graben, a 4.7km wide graben, lies along the central axis of the WVZ and has subsided >35m during the Holocene. An ~8km long leveling profile across the graben indicates a subsidence rate of ~1mmyr−1 from 1990 to 2007, relative to the first (westernmost) benchmark. Modeled GPS velocities from 1994 to 2003 estimate a spreading rate of 6.7±0.5mmyr−1 or 35% of the full plate motion rate and up to 6.0mmyr−1 subsidence. The combined geodetic observations show that the deformation zone is 10 times wider than the graben width. We utilize these geodetic observations to test the effects of ridge thermal structure on the kinematics across divergent boundaries. We apply a nonlinear rheology, thermomechanical model implemented in a finite element model. A 700°C isotherm is applied for the brittle to ductile transition in the crust, representing a dry olivine rheology. We adjust the depth of this isotherm to solve for the best fit model. The best fit model indicates that the 700°C isotherm is at 8km depth below the ridge axis, which results in an average thermal gradient of 87.5°Ckm−1 in the upper crust. The thermomechanical model predicts a subsidence rate of 4mmyr−1, comparable to our geodetic observations.
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| 5. |
- Islam, Md. Tariqul, 1980
(författare)
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Least Square Approach to Estimate 3D Coordinate Transformation Parameters: A Case of Three Reference Systems in Sweden
- 2014
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Ingår i: International Journal of Remote Sensing and GIS. - 2277-9051. ; 3:3, s. 30-38
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Tidskriftsartikel (refereegranskat)abstract
- Seven parameters of Helmert transformation are estimated using three-dimensional Cartesian coordinates in Sweden. Here, two cases are studied. Cartesian coordinates of RT90 and SWEREFF 93 in mm level accuracy for Case A are generated from secondary source. However for Case B, coordinates have been obtained by a field measurement. Trimble differential GPS has been used to measure coordinate in both SWEREFF 99 TM and RT90 reference systems in Gothenburg region, Sweden. It provides the coordinates in decimeter level accuracy. Helmert transformation parameters are estimated by applying MATLAB code. Seven parameters of Helmert transformation between RT90 and SWEREFF 93, and RT90 and SWEREFF 99 TM, and vice-versa are estimated. The average variance-covariance and, difference between measured and transformed coordinates in Case A is estimated to 3.86e-7 and 0.082 meter, respectively. However in Case B, the estimated transformation parameters is poor due to low level accuracy of measured coordinates and not fit in proper Cartesian system since the height component in 3D coordinate system provides geoid height which does not correspond to Cartesian coordinate. Therefore it gives high average variance-covariance as to 0.2165 and difference between measured and transformed coordinates to 5.498 meter. So estimation of Helmert transformation parameters requires Cartesian coordinates with high accuracy.
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| 6. |
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| 7. |
- Islam, Md Tariqul
(författare)
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Quantification of Eroded and Deposited Riverbanks and Monitoring River's Channel Using RS and GIS
- 2009
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Ingår i: 2009 17TH INTERNATIONAL CONFERENCE ON GEOINFORMATICS. - NEW YORK : IEEE. - 9781424445622 ; , s. 178-182
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Konferensbidrag (refereegranskat)abstract
- The Padma and the Jamuna are the two of three major rivers those flow within few meters of height in Bangladesh. These rivers are very important in context of water navigation, irrigation, fishing and fresh water for down stream. On the other side, those are the rivers of erosion of riverbanks and deposition of sandbanks. The main objective of this study is to estimate the eroded and deposited banks of the Padma and the Jamuna and to visualize movement of their channels from 1977 to 2000. Three dates of Landsat images were acquired in 1977 (MSS), 1989 (TM) and 2000 (ETM+) over the study area. Processing of Landsat images was performed by PCI Geomatics and ArcGIS 9.2 was used for quantification of eroded and deposited land covers. Subset the data was performed as preprocessing of image. Seven types of land covers of level I were decided for imagery classification where settlement areas were separated using mask. Supervised classification method was applied using 200 pixels for each class as test set other than training area for accuracy assessment where average accuracies of 85.64%, 89.14% and 90.07% were achieved in 1977 (MSS), 1989 (TM) and 2000 (ETM+) respectively. ArcGIS 9.2 was used to transfer the classified images to GIS layer for quantification. Eroded and deposited areas of the Padma and the Jamuna between the years were calculated by superimposition and pair-wise comparison of river layers in 1977-89 and 1989-2000. From 1977 to 1989 and 1989 to 2000, estimated average erosion was 5436 and 2954 hectares/year and deposition was 773 and 1954 hectares/year correspondingly. In 1977, 1989 and 2000, estimated rivers area in the study area were 2789, 3348, 3458 sq km. During this period, there was more erosion than deposition which indicates that rivers were getting wider. The confluence point of the Padma and the Jamuna was migrated toward southeast and their channels were moved by erosion and deposition following their direction. General trend of channel movement of the Padma was toward south but for the Jamuna, it was quite irregular.
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| 8. |
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| 9. |
- Islam, Md. Tariqul, 1980, et al.
(författare)
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Rheological responses to plate boundary deformation at the Eastern Volcanic Zone in Iceland
- 2017
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Ingår i: Tectonophysics. - : Elsevier BV. - 0040-1951. ; 717, s. 16-26
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Tidskriftsartikel (refereegranskat)abstract
- Located on the mid-Atlantic ridge, Iceland allows for direct measurement of crustal deformation. Global Positioning System (GPS) data from the Eastern Volcanic Zone (EVZ), Iceland, and crustal deformation of the rift near its southern end at 64°N show a spreading rate of 13.8 ± 1.8 mm yr− 1. About 90% of the deformation occurs in an 80 to 90-km wide zone. To understand how the rheology of the lithosphere influences rifting, we applied a thermo-mechanical stretching model that includes thermal states in Iceland using temperature- and stress-dependent wet and dry olivine rheology. We attempt to reproduce the thermal structure of a rift by defining 700 °C from 5- to 15-km depth at the rift axis that leads to variation in rheological structure, and to estimate the layer (from surface to a depth of 700 °C) where the elastic deformation of the lithosphere is the greatest. At a fixed spreading rate, the deformation field is controlled by the sub-surface thermal state. The vertical subsidence rate at the ridge axis increases almost linearly as the half-velocity increases. The best fitted model suggests a thermal gradient of ~ 54 °C km− 1 at depth below where 700 °C occurs at the ridge axis. The models have little sensitivity to the wet or dry olivine rheology. Estimated viscosity is ~ 1E19 Pa s at 20-km depth at the ridge axis and ~ 1E18 Pa s up to 100-km depth in the model. The spreading rate influences the tangential (non-linearity) shape of the deformation field, and a change in spreading rate affects the deformation field the most. After spreading velocity, the model's second most sensitive parameter is the location of the 700 °C at the rift axis. The thermomechanical model confirms that the rheological responses at the central part of the rift zone in the EVZ, Iceland caused of plate spreading is nonlinear, comparable with surface deformation observed by GPS measurement.
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| 10. |
- Islam, Md. Tariqul, 1980
(författare)
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RIVER CHANNEL MIGRATION: A REMOTE SENSING AND GIS ANALYSIS
- 2010
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Ingår i: Proceedings of ESA Living Planet Symposium. 28 June - 2 July 2010, Bergen, Norway / edited by H. Lacoste-Francis. - 1609-042X. - 9789292212506 ; :SP-686
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Konferensbidrag (refereegranskat)abstract
- Remote sensing and geographic information system provide tools for quantitative and qualitative river morphological analysis. Bangladesh is a riverine, flood prone country and, the Padma and the Jamuna are two of major three rivers in the country. The aim of this research is to monitor the channel migration of the Padma and the Jamuna rivers since 1977 to 2004 using remote sensing and GIS. Four scenes for dry season’s cloud free Landsat images were used in this study. Images were processed using PCI Geomatica and ArcGIS 9.3 was used for GIS analysis. The Landsat images were visualized and identified nine locations to investigate the channel migration. The images were classified into two broad categories, i.e. water and nonwater body. ArcGIS 9.3 was used to transfer these classified images into GIS layers. A standard measurement tool of ArcGIS was applied to measure the movement of river channel based on initial river channel in 1977. General trend of the Padma and the Jamuna river channel migration at locations A, B, C, D, F, G, H and I towards north, northeast and southwest eventually, north, northeast, east, east, west and west, respectively. The confluence point of the Padma and Jamuna (at location E) migrated toward southeast with high rate. During 1977-2004, it migrated about 9000m toward southeast. Trend of migration of the confluence point was faster than any other locations in the channel of the Padma river.
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| 11. |
- Islam, Md. Tariqul, 1980, et al.
(författare)
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Temperature-Dependent Newtonian Rheology in Advection-Convection Geodynamical Model for Plate Spreading in Eastern Volcanic Zone, Iceland
- 2015
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Ingår i: Journal of Geoscience and Environment Protection. - : Scientific Research Publishing, Inc.. - 2327-4336 .- 2327-4344. ; 3, s. 14-26
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Tidskriftsartikel (refereegranskat)abstract
- Geodynamic process as advection-convection of the Mid-Atlantic Ocean Ridge (MAR), that is exposed on land in Iceland is investigated. Advection is considered for the plate spreading velocity. Geodetic GPS data during 2000-2010 is used to estimate plate spreading velocity along a profile in the Eastern Volcanic Zone (EVZ), Iceland striking N102˚E, approximately parallel to the NUVEL-1A spreading direction between the Eurasian and North American plates. To predict subsurface mass flow patterns, temperature-dependent Newtonian rheology is considered in the finite-element models (FEM). All models are considered 2-D with steady-state, incompressible rheology whose viscosity depends on the subsurface temperature distribution. The thickness of lithosphere along the profile in the EVZ is identified by 700˚C isotherm and 1022 Pa s iso-viscosity, those reach 50 ± 3 km depth at distance of 100 km from rift axis. Geodetic observation and model prediction results show the ~90% of spreading is accommodated within ~45 km of the rift axis in each direction. Model predicts ~8.5 mm∙yr−1 subsidence at the surface of rift center when magmatic plumbing is inactive. The rift center (the highest magmatic influx is ~11 mm∙yr−1) in model shifts ~10 - 20 km west to generate observed style surface deformation. The spreading velocity, isotherm and depth of isotherm are the driving forces resulting in the surface deformation. These three parameters have more or less equal weight. However, as the center of deformation in the EVZ shifts and most of the subsidence takes place in the volcanic system that is currently the active which is the located of plate axis.
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| 12. |
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| 13. |
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| 14. |
- Islam, Md. Tariqul, 1980
(författare)
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VEGETATION CHANGES OF SUNDARBANS BASED ON LANDSAT IMAGERY ANALYSIS BETWEEN 1975 AND 2006
- 2014
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Ingår i: Landscape & Environment. - 1789-4921 .- 1789-7556. ; 8:1, s. 1-9
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Tidskriftsartikel (refereegranskat)abstract
- paper is to show changes in vegetation cover of Sundarbans since 1975 using Landsat imagery. Normal - ized Difference Vegetation Index is applied to quantify and qualify density of vegetation on a patch of land. Estimated land area (excluded water body) of this forest is 66% in Bangladesh, and 34% in India, respectively. Net erosion since 1975 to 2006 is ~5.9%. In vicinity of human settlement, areal changes are not observed since 1975. The mangrove forest is decreased by 19.3% due severe tropical cyclone in 1977 and 1988. Moreover, the dense forest is damaged by about 50%. However, more than 25 years is taken by Sundarbans to recover from damage by a severe tropical cyclone. The biodiversity of Sundarbans depends to fresh water flow through it. Therefore, the future of Sundarbans depends to the impact of climate change which has further effect to increasing intensity and frequency of severe tropical cyclone and salinity in water channels in Sundarbans
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| 15. |
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| 16. |
- Mahajan, Anubha, et al.
(författare)
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Multi-ancestry genetic study of type 2 diabetes highlights the power of diverse populations for discovery and translation
- 2022
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Ingår i: Nature Genetics. - : Springer Nature. - 1061-4036 .- 1546-1718. ; 54:5, s. 560-572
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Tidskriftsartikel (refereegranskat)abstract
- We assembled an ancestrally diverse collection of genome-wide association studies (GWAS) of type 2 diabetes (T2D) in 180,834 affected individuals and 1,159,055 controls (48.9% non-European descent) through the Diabetes Meta-Analysis of Trans-Ethnic association studies (DIAMANTE) Consortium. Multi-ancestry GWAS meta-analysis identified 237 loci attaining stringent genome-wide significance (P < 5 x 10(-9)), which were delineated to 338 distinct association signals. Fine-mapping of these signals was enhanced by the increased sample size and expanded population diversity of the multi-ancestry meta-analysis, which localized 54.4% of T2D associations to a single variant with >50% posterior probability. This improved fine-mapping enabled systematic assessment of candidate causal genes and molecular mechanisms through which T2D associations are mediated, laying the foundations for functional investigations. Multi-ancestry genetic risk scores enhanced transferability of T2D prediction across diverse populations. Our study provides a step toward more effective clinical translation of T2D GWAS to improve global health for all, irrespective of genetic background. Genome-wide association and fine-mapping analyses in ancestrally diverse populations implicate candidate causal genes and mechanisms underlying type 2 diabetes. Trans-ancestry genetic risk scores enhance transferability across populations.
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| 17. |
- Sturkell, Erik, 1962, et al.
(författare)
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Continuous subsidence in the Thingvellir rift graben, Iceland: Geodetic observations since 1966 compared to rheological models of plate spreading
- 2013
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Ingår i: AGU (American Geophysical Union) Fall Meeting, 9-13 December, 2013, San Francisco, USA.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Plate spreading across the Mid-Atlantic Ridge in south Iceland is partitioned between overlapping rift segments - the Western Volcanic Zone (WVZ) and the Eastern Volcanic Zone. The Thingvellir graben lies along the central axis of the WVZ. A central piece of the graben, between main boundary faults spaced 4.7 km apart, has subsided over 30 m since the postglacial lava last covered it about 9000 years ago. A rifting episode without eruptions occurred in 1789. An ~7 km long leveling profile crosses the graben was initially measured in 1966. It has been remeasured five times, most recently in 1990 and 2007. A subsidence of about 1.5 mm/year is observed along the central part of the profile, compared to its end. GPS measurements since 1994 document a spreading rate of 3.5 mm/yr or less, distributed over the ~50 km width of the WVZ. This is only a fraction of full spreading between the North American and Eurasian plates in South Iceland, which is 18.7 mm/yr in direction N103°E according to the MORVEL plate motion model and mostly accommodated by the EVZ. The GPS vertical velocities, corrected for post-glacial rebound, suggest maximum subsidence of ~4.00 mm/yr in the center of the rift, and a broad (>50 km) zone of subsidence across the WVZ. The length of the leveling profile is short compared to the width of the zone of subsidence, so it only captures a fraction of the overall subsidence. A two-dimensional (length and depth) finite element model (FEM), considering a temperature-dependent non-linear rheology is used to fit the observed surface deformation. The model is stretched to reproduce the observed deformation, with varying rheological parameters and thermal boundary conditions. The model considers, in particular, different depth to 700°C isotherm at the rift axis. The best-fit model, solved by minimizing the residual between the observed and modeled surface displacements, is found for a 700°C isotherm at 5 km depth at the rift axis, with a thermal gradient of 140°C/km above. This depth is consistent with a locking depth inferred from previous elastic dislocation models. The magma inflow in the system is not sufficient to keep up with the subsidence caused by the stretching, causing subsidence. The combined observations and model show that the deformation zone of the WVZ is almost ten times larger than the width of the central segment of the Thingvellir graben.
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