scholarly journals New Geodetic and Gravimetric Maps to Infer Geodynamics of Antarctica with Insights on Victoria Land

2018 ◽  
Vol 10 (10) ◽  
pp. 1608 ◽  
Author(s):  
Antonio Zanutta ◽  
Monia Negusini ◽  
Luca Vittuari ◽  
Leonardo Martelli ◽  
Paola Cianfarra ◽  
...  
Keyword(s):  
Regional Scale ◽  
Bouguer Anomaly ◽  
Gravity Anomalies ◽  
Active Role ◽  
International Gnss Service ◽  
Gravity Station ◽  
Continental Scale ◽  
Victoria Land ◽  
Euler Pole ◽  
Uplift Rates

In order to make inferences on the geodynamics of Antarctica, geodetic and gravimetric maps derived from past and new observations can be used. This paper provides new insights into the geodynamics of Antarctica by integrating data at regional and continental scales. In particular, signatures of geodynamic activity at a regional extent have been investigated in Victoria Land (VL, Antarctica) by means of Global Navigation Satellite System (GNSS) permanent station observations, data from the VLNDEF (Victoria Land Network for Deformation control) discontinuous network, and gravity station measurements. At the continental scale, episodic GNSS observations on VLNDEF sites collected for 20 years, together with continuous data from the International GNSS Service (IGS) and Polar Earth Observing Network (POLENET) sites, were processed, and the Euler pole position assessed with the angular velocity of the Antarctic plate. Both the Bouguer and the free-air gravity anomaly maps were obtained by integrating the available open-access geophysics dataset, and a compilation of 180 gravity measurements collected in the VL within the Italian National Program for Antarctic Research (PNRA) activities. As a result, new evidence has been detected at regional and continental scale. The main absolute motion of VL is towards SE (Ve 9.9 ± 0.26 mm/yr, Vn −11.9 ± 0.27 mm/yr) with a pattern similar to the transforms of the Tasman and Balleny fracture zones produced as consequence of Southern Ocean spreading. Residual velocities of the GNSS stations located in VL confirm the active role of the two main tectonic lineaments of the region, the Rennick–Aviator and the Lillie–Tucker faults with right-lateral sense of shear. The resulting VL gravity anomalies show a NW region characterized by small sized Bouguer anomaly with high uplift rates associated and a SE region with low values of Bouguer anomaly and general subsidence phenomena. The East and West Antarctica are characterized by a different thickness of the Earth’s crust, and the relative velocities obtained by the observed GNSS data confirm that movements between the two regions are negligible. In East Antarctica, the roots of the main subglacial highlands, Gamburtsev Mts and Dronning Maud Land, are present. The Northern Victoria Land (NVL) is characterized by more scattered anomalies. These confirm the differences between the Glacial Isostatic Adjustment (GIA) modeled and observed uplift rates that could be related to deep-seated, regional scale structures.

Climate as the great equalizer of continental-scale erosion

2021 ◽  
Author(s):  
Gilby Jepson ◽  
Barbara Carrapa ◽  
Jack Gillespie ◽  
Ran Feng ◽  
Peter DeCelles ◽  
...  
Keyword(s):  
Central Asia ◽  
Regional Scale ◽  
Continental Scale ◽  
Active Tectonic ◽  
Tectonically Active ◽  
High Precipitation ◽  
Tectonic Boundaries ◽  
Great Equalizer ◽  
Tian Shan

<p>Central Asia is one of the most tectonically active and orographically diverse regions in the world and is the location of the highest topography on Earth resulting from major plate tectonic collisional events. Yet the role of tectonics versus climate on erosion remains one of the greatest debates of our time. We present the first regional scale analysis of 2526 published low-temperature thermochronometric dates from Central Asia spanning the Altai-Sayan, Tian Shan, Tibet, Pamir, and Himalaya. We compare these dates to tectonic processes (proximity to tectonic boundaries, crustal thickness, seismicity) and state-of-the-art paleoclimate simulations in order to constrain the relative influences of climate and tectonics on the topographic architecture and erosion of Central Asia. Predominance of pre-Cenozoic ages in much of the interior of central Asia suggests that significant topography was created prior to the India-Eurasia collision and implies limited subsequent erosion. Increasingly young cooling ages are associated with increasing proximity to active tectonic boundaries, suggesting a first-order control of tectonics on erosion. However, areas that have been sheltered from significant precipitation for extensive periods of time retain old cooling ages. This suggests that ultimately climate is the great equalizer of erosion. Climate plays a key role by enhancing erosion in areas with developed topography and high precipitation such as the Tian Shan and Altai-Sayan during the Mesozoic and the Himalaya during the Cenozoic. Older thermochronometric dates are associated with sustained aridity following more humid periods.</p>

scholarly journals Assessing the regional surface influence through Backward Lagrangian Dispersion Models for aircraft CO<sub>2</sub> vertical profiles observations in NE Spain

2010 ◽  
Vol 10 (3) ◽  
pp. 8103-8134
Author(s):  
A. Font ◽  
J.-A. Morguí ◽  
X. Rodó
Keyword(s):  
Regional Scale ◽  
Grid Cell ◽  
Particle Dispersion ◽  
Vertical Profiles ◽  
Lagrangian Particle ◽  
Mixing Ratios ◽  
Continental Scale ◽  
Lagrangian Dispersion ◽  
Threshold Criteria ◽  
Ne Spain

Abstract. A weekly climatology for 2006 composed of 96-h-backward Lagrangian Particle Dispersion simulations is presented for nine aircraft sites measuring vertical profiles of atmospheric CO2 mixing ratios along the 42° N parallel in NE Spain to assess the surface influence at a regional scale (102–103 km) at different altitudes in the vertical profile (600, 1200, 2500 and 4000 meters above the sea level, m a.s.l.). The Potential Surface Influence (PSI) area for the 96-h-backward simulations, defined as the air layer above ground with a thickness of 300 m, are reduced from the continental scale (~107 km2) to the watershed one (~104 km2), when a Residence Time Threshold Criteria (Rttc) greater than 500 s is imposed for each grid cell. In addition, this regional restricted information is confined during 50 h before the arrival for simulations centered at 600 and 1200 m a.s.l. At higher altitudes (2500 and 4000 m a.s.l.), the regional surface influence is only recovered during spring and summer months. For simulations centered at 600 and 1200 m a.s.l. sites separated by ~60 km may overlap 20–50% of the regional surface influences whereas sites separated by ~350 km as such do not overlap. The overlap for sites separated by ~60 km decreases to 8–40% at higher altitudes (2500 and 4000 m a.s.l.). A dense network of sampling sites below 2200 m a.s.l. (whether aircraft sites or tall tower ones) guarantees an appropriate regional coverage to properly assess the dynamics of the regional carbon cycle at a watershed scale (102–103 km length scale).

3D Gravity modeling of the volcanic island of Surtsey, Iceland

2021 ◽  
Author(s):  
sara sayyadi ◽  
Magnús T. Gudmundsson ◽  
Thórdís Högnadóttir ◽  
James White ◽  
Joaquín M.C. Belart ◽  
...  
Keyword(s):  
Sea Level ◽  
Gravity Data ◽  
Bouguer Anomaly ◽  
Gravity Modeling ◽  
Gravity Station ◽  
Effusive Activity ◽  
3D Gravity ◽  
Anomaly Map ◽  
Bouguer Anomaly Map ◽  
Drill Cores

&lt;p&gt;The formation of the oceanic island Surtsey in the shallow ocean off the south coast of Iceland in 1963-1967 remains one of the best-studied examples of basaltic emergent volcanism to date. The island was built by both explosive, phreatomagmatic phases and by effusive activity forming lava shields covering parts of the explosively formed tuff cones. &amp;#160;Constraints on the subsurface structure of Surtsey achieved mainly based on the documented evolution during eruption and from drill cores in 1979 and in the ICDP-supported SUSTAIN drilling expedition in 2017(an inclined hole, directed 35&amp;#176; from the vertical). The 2017 drilling confirmed the existence of a diatreme, cut into the sedimentary pre-eruption seafloor (Jackson et al., 2019).&amp;#160;&lt;/p&gt;&lt;p&gt;We use 3D-gravity modeling, constrained by the stratigraphy from the drillholes to study the structure of the island and the underlying diatreme. &amp;#160;Detailed gravity data were obtained on Surtsey in July 2014 with a gravity station spacing of ~100 m. Density measurements for the seafloor sedimentary and tephra samples of the surface were carried out using the ASTM1 protocol. By comparing the results with specific gravity measurements of cores from drillhole in 2017, a density contrast of about 200 kg m&lt;sup&gt;-3&lt;/sup&gt; was found between the lapilli tuffs of the diatreme and the seafloor sediments.&amp;#160; Our approach is to divide the island into four main units of distinct density: (1) tuffs above sea level, (2) tuffs below sea level, (3) lavas above sea level, and (4) a lava delta below sea level, composed of breccias over which the lava advanced during the effusive eruption.&amp;#160; The boundaries between the bodies are defined from the eruption history and mapping done during the eruption, aided by the drill cores.&amp;#160;&lt;/p&gt;&lt;p&gt;A complete Bouguer anomaly map is obtained by calculating a total terrain correction by applying the Nagy formula to dense DEMs (5 m spacing out to 1.2 km from station, 200 m spacing between 1.2 km and 50 km) of both island topography and ocean bathymetry.&amp;#160; Through the application of both forward and inverse modeling, using the GM-SYS 3D software, the results provide a 3-D model of the island itself, as well as constraints on diatreme shape and depth.&lt;/p&gt;

scholarly journals On the topographic effects by Stokes’ formula

2014 ◽  
Vol 4 (1) ◽  
Author(s):  
L.E. Sjöberg
Keyword(s):  
Gravity Anomaly ◽  
Bouguer Anomaly ◽  
Gravity Anomalies ◽  
Geoid Height ◽  
Topographic Effects ◽  
Gravimetric Geoid ◽  
Bouguer Gravity ◽  
The Third ◽  
Stokes Formula ◽  
The Difference

AbstractTraditional gravimetric geoid determination relies on Stokes’ formula with removal and restoration of the topographic effects. It is shown that this solution is in error of the order of the quasigeoid-to-geoid difference, which is mainly due to incomplete downward continuation (dwc) of gravity from the Earth’s surface to the geoid. A slightly improved estimator, based on the surface Bouguer gravity anomaly, is also biased due to the imperfect harmonic dwc the Bouguer anomaly. Only the third estimator,which uses the (harmonic) surface no-topography gravity anomaly, is consistent with the boundary condition and Stokes’ formula, providing a theoretically correct geoid height. The difference between the Bouguer and no-topography gravity anomalies (on the geoid or in space) is the “secondary indirect topographic effect”, which is a necessary correction in removing all topographic signals.

Shape and depth solutions from gravity data using correlation factors between successive least‐squares residuals

Geophysics ◽  
1993 ◽  
Vol 58 (12) ◽  
pp. 1785-1791 ◽  
Author(s):  
El‐Sayed M. Abdelrahman ◽  
Hesham M. El‐Araby
Keyword(s):  
Least Squares ◽  
Shape Factor ◽  
Gravity Data ◽  
Bouguer Anomaly ◽  
Vertical Cylinder ◽  
Gravity Anomalies ◽  
Horizontal Cylinder ◽  
Amplitude Coefficient ◽  
Regional Component ◽  
Correlation Factors

The gravity anomaly expression produced by most geologic structures can be represented by a continuous function in both shape (shape factor) and depth variables with an amplitude coefficient related to the mass. Correlation factors between successive least‐squares residual gravity anomalies from a buried vertical cylinder, horizontal cylinder, and sphere are used to determine the shape and depth of the buried geologic structure. For each shape factor value, the depth is determined automatically from the correlation value. The computed depths are plotted against the shape factor representing a continuous correlation curve. The solution for the shape and depth of the buried structure is read at the common intersection of correlation curves. This method can be applied to a Bouguer anomaly profile consisting of a residual component caused by local structure and a regional component. This is a powerful technique for automatically separating the Bouguer data into residual and regional polynomial components. This method is tested on theoretical examples and a field example. In both cases, the results obtained are in good agreement with drilling results.

scholarly journals Interdecadal Variability of the South American Precipitation in the Monsoon Season

2015 ◽  
Vol 28 (2) ◽  
pp. 755-775 ◽  
Author(s):  
Alice M. Grimm ◽  
João P. J. Saboia
Keyword(s):  
Function Analysis ◽  
Monsoon Season ◽  
Regional Scale ◽  
The Other ◽  
Interdecadal Variability ◽  
Monthly Precipitation ◽  
Monsoon Precipitation ◽  
Climatic Indices ◽  
Continental Scale ◽  
Sst Anomalies

Abstract Interdecadal variability modes of monsoon precipitation over South America (SA) are provided by a continental-scale rotated empirical orthogonal function analysis, and their connections to well-known climatic indices and SST anomalies are examined. The analysis, carried out for austral spring and summer, uses a comprehensive set of station data assembled and verified for the period 1950–2000. The presented modes are robust, consistent with previous regional-scale studies and with modes obtained from longer time series over smaller domains. Opposite phases of the main modes show differences around 50% in monthly precipitation. There are significant relationships between the interdecadal variability in spring and summer, indicating local and remote influences. The first modes for both seasons are dipole-like, displaying opposite anomalies in central-east and southeast SA. They tend to reverse polarity from spring to summer. Yet the summer second mode and its related spring fourth mode, which affect the core monsoon region in central Brazil and central-northwestern Argentina, show similar factor loadings, indicating persistence of anomalies from one season to the other, contrary to the first modes. The other presented modes describe the variability in different regions with great monsoon precipitation. Significant connections with different combinations of climatic indices and SST anomalies provide physical basis for the presented modes: three show the strongest connections with SST-based indices, and two have the strongest connections with atmospheric indices. However, the main modes show connections with more than one climatic index and more than one oceanic region, stressing the importance of combined influence.

A combination of electrical resistivity, seismic refraction, and gravity measurements for groundwater exploration in Sudan

Geophysics ◽  
1981 ◽  
Vol 46 (9) ◽  
pp. 1304-1313 ◽  
Author(s):  
Ronald A. van Overmeeren
Keyword(s):  
Electrical Resistivity ◽  
Seismic Refraction ◽  
Bouguer Anomaly ◽  
Gravity Anomalies ◽  
Equivalence Problem ◽  
Groundwater Exploration ◽  
Fresh Groundwater ◽  
Subsequent Test ◽  
Additional Information ◽  
Electrical Sounding

In the savannah belt of central Sudan, near the town of Kosti, a regional geophysical survey has been carried out forming part of a groundwater project. Because of the presence of detectable and significant contrasts in physical properties of the subsoil, integrated use could be made of electrical resistivity, seismic refraction, and gravity methods. In the interpretation of multilayer electrical sounding curves, additional subsurface information such as lithological well descriptions and geophysical well logs is normally a necessity for solving the problems of equivalence. Along a profile in the eastern part of the area studied, where additional subsurface information was scarce, 16 vertical electrical soundings have been made. A preliminary simple mathematical interpretation suggested possibilities for the presence of fresh groundwater in the eastern part of the profile. In order to solve the equivalence problem, seismic refraction work was carried out at some selected places; that yielded additional information on depths to bedrock. These seismic data made possible a unique solution of the electrical sounding curves, from which it could be concluded that all groundwater in the area is saline. Subsequent test drilling confirmed these findings. A regional relative Bouguer anomaly map provided a picture of the general geologic structures and made possible rough estimates of depths to bedrock. In areas where the basement rocks are relatively close to the surface, as is the case with the profile presented, the gravity anomalies cannot be correlated with bedrock relief, because the effect is strongly influenced by lateral density variations within the bedrock itself. This is an example of a case where only an integrated application of several geophysical exploration methods can provide the desired hydrogeologic information in an acceptable balance between reliability and cost.

REGIONAL GRAVITY SURVEY IN NORTHEASTERN OKLAHOMA AND SOUTHEASTERN KANSAS

Geophysics ◽  
1956 ◽  
Vol 21 (1) ◽  
pp. 88-106 ◽  
Author(s):  
Kenneth L. Cook
Keyword(s):  
Structural Geology ◽  
Bouguer Anomaly ◽  
Gravity Anomalies ◽  
Close Correlation ◽  
Geodetic Survey ◽  
Gravity Survey ◽  
Complex Nature ◽  
Gravity Gradients ◽  
Anomaly Map ◽  
Regional Gravity

In 1948 the U. S. Geological Survey, in cooperation with the U. S. Coast and Geodetic Survey, made a regional gravity survey in northeastern Oklahoma and southeastern Kansas in connection with the studies of the deflection of the vertical. About 550 gravity stations were occupied with spacings of 5 to 10 miles in parts of 54 counties, and a Bouguer anomaly map, contoured at intervals of 5 milligals, was drawn. In southeastern Kansas there is a lack of correlation of regional gravity with known regional structural geology. The observed gravity anomalies are apparently caused principally by variations of density in the Precambrian basement and indicate a basement of complex nature, made up of rocks of contrasting properties, with a regional grain striking predominantly west or west‐northwest. In northeastern Oklahoma the several observed regional gravity anomalies indicate different degrees of correlation of regional gravity with regional structural geology. In the Precambrian highland area in Osage, Pawnee, and Creek Counties, there is a lack of correlation, as the gravity anomaly is probably caused chiefly by density contrasts within the basement complex. The anomaly associated with the Hunton arch is probably caused partly by structural relief of the rocks of pre‐Pennsylvanian age and partly by density contrasts within the basement, and thus indicates some correlation. The steep gravity gradients along the outer flanks of the Ozark uplift indicate good correlation with the subsurface geology. The great anomaly over the Arkansas basin, which indicates a close correlation, is probably caused largely—but perhaps not entirely—by downwarping of the basement and pre‐Pennsylvanian rocks.

Improvement of the conic prism model for terrain correction in rugged topography

Geophysics ◽  
1981 ◽  
Vol 46 (7) ◽  
pp. 1054-1056 ◽  
Author(s):  
Raymond J. Olivier ◽  
Réjean G. Simard
Keyword(s):  
Gravity Anomalies ◽  
Terrain Correction ◽  
Field Calculation ◽  
Bouguer Gravity ◽  
New Model ◽  
Gravity Station ◽  
Rugged Terrain ◽  
Rugged Topography ◽  
Terrain Corrections ◽  
Prism Model

Terrain corrections for Bouguer gravity anomalies are generally obtained from topographic models represented by flat‐topped compartments of circular zones, utilizing the so‐called Hayford‐Bowie (1912), or Hammer’s (1939) method. Some authors have introduced improved relief models for taking uniform slope into consideration (Sandberg, 1958; Kane, 1962; Takin and Talwani, 1966; Campbell, 1980). We present a new model that increases the accuracy of the calculation of terrain correction close to the gravity station in rugged terrain, especially when conventional templates with few zones are used in field calculation.

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