Values Of Density Contrast Research Articles

Subsurface Analysis on Ranu Grati Lineaments with Satellite Gravity Data

The lineaments with NE-SW direction formed by the Umbulan Spring, Banyubiru Spring, and Ranu Grati Maar in Pasuruan Regency indicate a geological structure. This structure is predicted to play a role in forming these springs and maar. Therefore, a study was conducted to identify the presence of these geological structures using the GGMPlus satellite gravity data. The data used in this study were 945 points with spacing intervals of about 200 to 300 meters. Satellite gravity data needs to be corrected so that the Complete Bouguer Anomaly (CBA) value is obtained, which can be used to determine the distribution of density contrast values ​​in the research area. Gridding is done by using a Second Vertical Derivative (SVD) filter to determine existing fault that results in the lineaments of the two springs and maar based on the second derivative value from CBA. It was found that the range of interpolated CBA values ​​in the study area was around 143 mGal to 150 mGal. SVD analysis indicates existing a fault plane exists through Umbulan Springs, Banyubiru Springs, and Ranu Grati Maar with E-W direction.

The evolution of high-density cores of the BOSS Great Wall superclusters

Context.High-density cores (HDCs) of galaxy superclusters that embed rich clusters and groups of galaxies are the earliest large objects to form in the cosmic web, and the largest objects that may collapse in the present or future.Aims.We aim to study the dynamical state and possible evolution of the HDCs in the BOSS Great Wall (BGW) superclusters at redshiftz ≈ 0.5 from the CMASS (constant mass) galaxy sample, based on the Baryon Oscillation Spectroscopic Survey (BOSS) in order to understand the growth and evolution of structures in the Universe.Methods.We analysed the luminosity density distribution in the BGW superclusters to determine the HDCs in them. We derived the density contrast values for the spherical collapse model in a wide range of redshifts and used these values to study the dynamical state and possible evolution of the HDCs of the BGW superclusters. The masses of the HDCs were calculated using stellar masses of galaxies in them. We found the masses and radii of the turnaround and future collapse regions in the HDCs of the BGW superclusters and compared them with those of local superclusters.Results.We determined eight HDCs in the BGW superclusters. The masses of their turnaround regions are in the range ofMT ≈ 0.4–3.3 × 1015 h−1 M⊙, and radii are in the range ofRT ≈ 3.5–7 h−1Mpc. The radii of their future collapse regions are in the range ofRFC ≈ 4–8 h−1Mpc. Distances between individual cores in superclusters are much larger: of the order of 25–35 h−1Mpc. The richness and sizes of the HDCs are comparable with those of the HDCs of the richest superclusters in the local Universe.Conclusions.The BGW superclusters will probably evolve to several poorer superclusters with masses similar to those of the local superclusters. This may weaken the tension with the ΛCDM model, which does not predict a large number of very rich and large superclusters in our local cosmic neighbourhood, and explains why there are no superclusters as elongated as those in the BGW in the local Universe.

3D inversion of gravity data with unstructured mesh and least-squares QR-factorization (LSQR)

Once inverting potential-field geophysical data an appropriate discretization of the model is required to accurately construct complicated geometries of the causative sources. Rectangular prisms (structured meshes) have limitations to recover and preserve the edges of real geological sources. Here an isoparametric finite-element (FE) methodology is used to design an unstructured mesh for use in 3D inverse modeling of gravity data. The calculation of the sensitivity kernel of the forward operator uses Gauss-Legendre quadrature rather than the analytic formulation. For the sake of instability of inversion operator in gravity data and to solve the Tikhonov norms term, the least-squares QR-factorization (LSQR) technique is used. This method is accompanied with weighted generalized cross-validation (WGCV) for selecting the optimum regularization parameter value. The depth weighting function is also incorporated in the formulation of the objective function to suppress the impact of shallow features and recover sources at an appropriate depth. The proposed algorithm was applied to noise-corrupted synthetic data along with a real case study where a gravity survey was used for iron exploration in Yazd province, central Iran. The obtained results of synthetic example indicated that the proposed 3D inversion method recovers the geometry and density contrast values which are similar to the true structures and its application on a real example data set recovers geologically reasonable complex structures. So, this modified algorithm is a type of smooth inversion for boundary detection and whole understanding of the physical property distribution of the subsurface.

Subsurface Modeling using Gravity and TDEM in Jiken, Blora Regency

Geophysics plays an essential role in imaging the subsurface condition of the earth. Gravity and time-domain electromagnetic method is geophysical method that can be used to visualize the subsurface condition. In this research, gravity and TDEM surveys have been carried out in Jiken, Blora Regency. Modeling technique is needed to obtain the subsurface model that bring information related to subsurface condition. Inversion modeling is applied separately to the gravity data and TDEM data, respectively. The density interface inversion modeling is used to gravity data.Subsurface condition is approached by three layers model with different density contrast values in each layer. In these schemes, the modeling process will determine the thickness for every layer. While for TDEM modeling,differential evolution technique is applied to model the TDEM data. The subsurface condition is approached by four layers model. In these schemes, the modeling process will determine the resistivity and thickness for every layer. Finally, the model obtained from gravity inversion modeling is integrated into the model from TDEM inversion data by overlaying the model.

From space to lithosphere: inversion of the GOCE gravity gradients. Supply to the Earth’s interior study

SUMMARY The emergence of high resolution satellite measurements of the gravitational field (GOCE mission) offers promising perspectives for the study of the Earth’s interior. These new data call for the development of innovant analysis and interpretation methods. Here we combine a forward prism computation with a Bayesian resolution approach to invert for these gravity gradient data configuration. We apply and test our new method on satellite data configuration, that is 225 km height with a global and homogeneous geographic distribution. We first quantify the resolution of our method according to both data and parametrization characteristics. It appears that for reasonable density contrast values (0.1 g cm−3) crustal structures have to be wider than ∼28 km to be detectable in the GOCE signal. Deeper bodies are distinguishable for greater size (35 km size at 50 km depth, ∼80 km at 300 km depth). We invert the six tensor components, among which five are independent. By carefully testing each of them and their different combinations, we enlighten a trade off between the recovery of data and the sensitivity to inversion parameters. We particularly discussed this characteristic in terms of geometry of the synthetic model tested (structures orientation, 3-D geometry, etc.). In terms of RMS value, each component is always better explained if inverted solely, but the result is strongly affected by the inversion parametrization (smoothing, variances, etc.). On the contrary, the simultaneous inversion of several components displays a significant improvement for the global tensor recovery, more dependent on data than on density variance or on smoothness control. Comparing gravity and gradient inversions, we highlight the superiority of the GG data to better reproduce the structures especially in terms of vertical location. We successfully test our method on a realistic case of a complex subduction case for both gradient and gravity data. While the imaging of small crustal structures requires terrestrial gravity data set, the longest wavelength of the slab is well recovered with both data sets. The precision and homogeneous coverage of GOCE data however, counterbalance the heterogeneous and often quite non-existence coverage of terrestrial gravity data. This is particularly true in large areas which requires a coherent assemblage of heterogeneous data sets, or in high relief, vegetally covered and offshore zones.

Kantorovich-Rubinstein misfit for inverting gravity-gradient data by the level-set method

We have developed a novel Kantorovich-Rubinstein (KR) norm-based misfit function to measure the mismatch between gravity-gradient data for the inverse gradiometry problem. Under the assumption that an anomalous mass body has an unknown compact support with a prescribed constant value of density contrast, we implicitly parameterize the unknown mass body by a level-set function. Because the geometry of an underlying anomalous mass body may experience various changes during inversion in terms of level-set evolution, the classic least-squares ([Formula: see text]-norm-based) and the [Formula: see text]-norm-based misfit functions for governing the level-set evolution may potentially induce local minima if an initial guess of the level-set function is far from that of the target model. The KR norm from the optimal transport theory computes the data misfit by comparing the modeled data and the measured data in a global manner, leading to better resolution of the differences between the inverted model and the target model. Combining the KR norm with the level-set method yields a new effective methodology that is not only able to mitigate local minima but is also robust against random noise for the inverse gradiometry problem. Numerical experiments further demonstrate that the new KR norm-based misfit function is able to recover deep dipping flanks of SEG/EAGE salt models even at extremely low signal-to-noise ratios. The new methodology can be readily applied to gravity and magnetic data as well.

Intrinsic Metastability of the α′ Phase and Its Partial Transformation into α Crystals during Isothermal Cold-Crystallization of Poly(l-lactide)

Structural evolution of poly(l-lactide) during cold-crystallization at 80 °C was examined via simultaneous small/wide-angle X-ray scattering (SAXS/WAXS), Fourier-transform infrared spectroscopy (FTIR), and differential scanning calorimetry (DSC). The incipient α′ crystals of loosely packed 107 helices, formed at tc = 200 s as detected via both WAXS and FTIR, were hardly identifiable via SAXS or DSC due to its low values of density contrast or latent heat (initially ΔHα′ ≈ 12 J/g, gradually reaching 74 J/g near the end of crystallization, in contrast to ΔHα ≈ 140 J/g), was already large in lateral size (with coherence length Λ200/110 ≈ 35 nm, increasing to 50 nm during tc = 200–400 s and remained little changed afterward). Once formed, the α′ crystals underwent continuous and persistent perfection for decreasing lattice spacing and partially transformed to smaller α crystals (tc ≈ 800–1800 s, up to a saturated population ratio of 1:4 between α and α′ phases), followed by slower yet steady increases in SAXS invariant without significant changes in the α and α′ contents for tc > 1800 s. It is concluded that the α′ form is a transient structure of continuously increasing packing density and latent heat toward the α form, reminiscent of the mesomorphic phase as precursors to stable crystals in other polymers. Nevertheless, transformation to α crystals occurred when the lattice parameters of the α′ phase were closer but still finitely different from those of the α phase and that the conversion between the two phases was limited in this isothermal case. Both observations suggest that, in spite of the transient nature of the α′ phase, the final transformation step to the stable α form is still achieved via a first-order route.

3D object-oriented image analysis in 3D geophysical modelling: Analysing the central part of the East African Rift System

Non-uniqueness of satellite gravity interpretation has traditionally been reduced by using a priori information from seismic tomography models. This reduction in the non-uniqueness has been based on velocity–density conversion formulas or user interpretation of the 3D subsurface structures (objects) based on the seismic tomography models and then forward modelling these objects. However, this form of object-based approach has been done without a standardized methodology on how to extract the subsurface structures from the 3D models. In this research, a 3D object-oriented image analysis (3D OOA) approach was implemented to extract the 3D subsurface structures from geophysical data. The approach was applied on a 3D shear wave seismic tomography model of the central part of the East African Rift System. Subsequently, the extracted 3D objects from the tomography model were reconstructed in the 3D interactive modelling environment IGMAS+, and their density contrast values were calculated using an object-based inversion technique to calculate the forward signal of the objects and compare it with the measured satellite gravity. Thus, a new object-based approach was implemented to interpret and extract the 3D subsurface objects from 3D geophysical data. We also introduce a new approach to constrain the interpretation of the satellite gravity measurements that can be applied using any 3D geophysical model.

Subsurface geometry and structural evolution of La Gomera island based on gravity data

We hereby present a new Bouguer gravity map of the La Gomera island (Canarian Archipelago), which is analysed and interpreted by means of a 3-dimensional inversion, in order to contribute to the knowledge of the structural setting of this volcanic island and its evolutionary history. A land gravity data set covering the whole island of La Gomera is used in combination with offshore measurements to achieve a better determination of the gravity field in areas near the coasts. The study of this map let us to shed some light on the hypothesis established about the volcanism of this island. Moreover, it shows the information that is hidden from a geological surface exploration, modelling deep sections of the crust in La Gomera, which have been unknown until now. A first interpretation of the Bouguer gravity anomaly is achieved from 1) the residual gravity map calculated by removing a regional component and 2) the total horizontal gradient of the gravity. These residual and derivative maps allow us to identify the horizontal location and borders of the shallowest gravity sources. This provides a useful tool to study the structures associated to the latest periods of the volcanism in the area. Moreover, the information so obtained supports the hypothesis about the migration of volcanic activity towards the south of the island. Subsequently, an inversion process is carried out looking for the 3D-modelisation of the sources of the observed gravity field, which provides a comprehensive view of the structures in volcanic environments. The inversion technique used is based on a genetic algorithm (GA) applied upon a prismatic partition of the subsoil volume, and adopting a priori values of density contrast (positive and negative). The main advantage of this method is that let us to model deep and shallow bodies which exhibit very different geometries and density contrasts. So, results indicate that this inversion strategy can be very effective for characterization of volcanic structures, improving the information from previous geologic and volcanologic studies. The inversion model obtained shows correlation between several sources of the gravity field and the volcanic units associated with the growth of La Gomera Island. The main gravity source of this model is associated with the oldest unit, called the Basal Complex. This unit corresponds to the first submarine growth stage and it is modelled as the most important and deepest high density structure. According to previous geological studies, the following edifice (Old Edifice) was also submarine in its initial phases, later being represented by a wide basaltic shield volcano. The original location and morphology of this Old Edifice is deduced from the distribution of positive density contrasts that appears in the model. Moreover, other gravity field sources are identified and associated to several feeding systems of this stage of the volcanism in La Gomera. The shallowest sections of the model let us recognise the distribution of light material inside the Vallehermoso caldera, surrounded by high density structures. This gives us some insight into the internal structure and morphology of the caldera, pointing to a vertical collapse origin followed by erosion and other destructive processes. Finally, other conclusions are obtained from the correlation found between the sources of the gravity field and the migration of the volcanic activity towards the southern area of the island.

Material properties of euphausiids and other zooplankton from the Bering Sea

Acoustic assessment of Bering Sea euphausiids and their predators can provide useful data for ecosystem studies if the acoustic scattering characteristics of these animals are known. The amount of acoustic energy that is scattered by different marine zooplankton taxa is strongly affected by the contrast of the animal's density (g) and sound speed (h) with the surrounding seawater. Density and sound speed contrast were measured in the Bering Sea during the summer of 2008 for several different zooplankton and nekton taxa including: euphausiids (Thysanoessa inermis, Thysanoessa raschii, and Thysanoessa spinifera), copepods, amphipods, chaetognaths, gastropods, fish larvae, jellyfish, and squid. Density contrast values varied between different taxa as well as between individual animals within the same species. Sound speed contrast was measured for monospecific groups of animals and differences were found among taxa. The range, mean, and standard deviation of g and h for all euphausiid species were: g = 1.001-1.041; 1.018 ± 0.009 and h = 0.990-1.017; 1.006 ± 0.008. Changes in the relationship between euphausiid material properties and animal length, seawater temperature, seawater density, and geographic location were also evaluated. Results suggest that environmental conditions at different sample locations led to significant differences in animal density and material properties.

The crustal structure of El Hierro (Canary Islands) from 3-D gravity inversion

El Hierro is the youngest and westernmost island of the Canarian Archipelago. Due to its singular and interesting characteristics, with extensive landsliding, studying its crustal structure can provide very useful information about its origin and evolution. With this aim, we use the gravity inversion methodology obtaining a crustal model of mass distribution. We performed a gravity survey of the entire island, completing the gravity anomaly map of this area with marine data from the United States Geological Survey. The calculated Bouguer gravity anomaly map was studied using a covariance analysis and the least squares technique. To obtain crustal information from these data, we used a 3D gravity inversion based on genetic algorithms (GA). Thus, our inversion technique aims to determine the geometry of the sources of the observed gravity field, upon a prismatic partition of the subsoil volume, and adopting a priori density contrast values. The results of this gravity study of El Hierro Island show the correlation of several volcanic structures with the distribution of the gravity field sources. The characteristic triple rift system of the island is associated with low-density areas, and the older volcanic stages with high-density structures. We also found differences among the structures related to the several landslides, which helped the island takes shape.

The X-ray emission mechanism in the protostellar jet HH 154

We study the mechanism causing the X-ray emission recently detected in protostellar jets, by performing a detailed modeling of the interaction between a supersonic jet originating from a young stellar object and the ambient medium, for various values of density contrast, ν, between the ambient density and the jet, and of Mach number, M; radiative losses and thermal conduction have been taken into account. Here we report a representative case which reproduces, without any ad hoc assumption, the characteristics of the X-ray emission recently observed in the protostellar jet HH 154. We find that the X-ray emission originates from a localized blob, consistent with observations, which moves with velocity v ∼ 500 km s −1 ; we therefore predict the X-ray source to have a detectable proper motion.

Monostatic and bistatic scattering from a density contrast surface

Chu’s formalism for the impulse response of a point source to a density contrast isovelocity wedge [J. Acoust. Soc. Am. 86, 1883–1896 (1989)] is of significant practical importance, since it facilitates the extension of wedge diffraction boundary scattering models to rough penetrable surfaces. The method is used here to study scattering from an experimental surface described by Li et al. [J. Acoust. Soc. Am. 96, 3715–3720 (1994)]. The geometry contains both interior and exterior wedges, and allows the diffracted scattering component to be studied independently of the reflected component. For density contrast values which emulate rigid boundary conditions, the formalism correctly models the experimental results, and duplicates predictions of the Biot–Tolstoy solution for a rigid wedge [J. Acoust. Soc. Am. 29, 381–391 (1957)]. The formalism is then used to investigate an assumption commonly made in boundary scattering work, i.e., that scattering levels can be effectively estimated by scaling the predictions of a rigid surface scattering model by the reflectivity of the surface. The results suggest that the assymption is most valid for monostatic (backscattering) configurations, and less good for bistatic cases, with increasing differences occurring between interior and exterior wedge geometries. [Work supported by ONR.]

Gravity anomalies of a vertical cylinder of polygonal cross-section and their inversion

The equation for the gravity anomaly of a vertical cylinder with a polygonal cross-section is derived. An algorithm for inverting the gravity anomalies of the model is developed and the related software, coded in FORTRAN 77, is presented in the program GPCYLNIN. The input to the computer consists of anomaly values, their distance coordinates, and initial values of horizontal coordinates of the edges of the cylinder. Initial values of density contrast and coefficients defining linear regional gradient are generated by the computer. Then all initial parameters of the model are revised iteratively, based on an optimization technique.

A generalized target strength model for euphausiids, with applications to other zooplankton

A hybrid model has been developed that generates predictions of euphausiid target strengths similar to those observed by direct measurement. The controlling variables of the model account for the size, shape, orientation, and stochastic nature of orientation. Sound speed and density contrast values used are within the range of those directly observed. This suggests that it is possible to produce a generalized target strength prediction for euphausiids like those available for fish. Euphausiids appear to be better generalized as a bent cylindrical or bent spheroid targets rather than spherical targets, at least for frequencies greater than 100 kHz. Although the model is based on a single, limited data set, its predictions compare well with the results, of a number of recently published measurements and models of target strength. The model also resolves some puzzling contradictions of target strength frequency dependency previously observed, but unexplained. A number of items were determined to be needed to complete or further refine such hybrid models: Target strength measurements for more sizes, species, and frequencies (especially below 50 kHz and above 420 kHz) are most prominent among these.

Inversion of regional gravity anomalies and main features of the deep crustal geology of India

Long-wavelength gravity field variations provide an important geophysical tool for delineating structural features of the deeper parts of the Earth's interior. Continuous developments in data-processing and inversion techniques have led to refinements in regional- as well as planetary-scale structural models. The present work uses the free-air gravity data of the Indian subcontinent to derive causative density contrast structures. The model obtained by assuming the point mass sources at a constant depth of 40 km (based on Deep Seismic Sounding Studies) reflects the known tectonic and geological provinces of the Indian subcontinent well. Interestingly, more than two-thirds of India exhibits “low”-density contrast values, with the lowest point occurring in the vicinity of the Sarda depression (which possibly hides a broken part of the Tethys trench). In general, the plateaus and uplifts are depicted as density contrast “highs”, while basins and depressions are associated with “lows”. An S-N traverse close to 78° E longitude confirms these findings. Further, the study confirms the postulated Burrard's hidden trough (Belgaum-Nellore) and additionally identifies 1. (1) a new hidden structural ridge running along the Ahmednagar-Hyderabad line, and 2. (2) a trough with an axis along the Mandya-Salem-Tanjavur line. All of these deformations exhibit connections with the seafloor spreading process, as they parallel the Carlsberg ridge in the Indian ocean in the south, and the Himalayan fold axis in the collision zone of the Indian and Eurasian plates.

Formation of Gravitationally Bound Primordial Gas Clouds

The formation of gravitationally bound systems from primordial gas is studied by . means of Tolman's solution for dust-like matter. The critical values of density contrast and its growth rate at an initial epoch are derived, which are necessary for an inhomogeneity to condense into a bound system before the appearance of the oldest stars. The matter distributions in an . isolated inhomogeneity and an inhomogeneity included in a larger one (which will be a cluster of gas clouds) are followed with time by assuming simple models for inhomogeneities, and it is shown how the bound region spreads outwards. Moreover, the minimum mass of fragments into which the gas clouds may break up is examined. The formation of galaxies which are dispersed everywhere at present in the universe has been studied by many authors. Some of them have assumed that small density fluctuations in an early stage of cosmic evolution grow owing to gravitational instability, until they condense into protogalaxies. However, on Lifshitz's assumption!) that the early stage was very quiet and the fluctua­ tions were statistical, gravitational instability was not effective. This is because the density contrasts of the statistical fluctuations corresponding to galaxies are too small (r-J 10- 34 ) to grow to gravitationally bound systems within the cosmic age. The linearized theories were sufficient for the description of such small fluctuations. After Lifshitz, the behavior of the fluctuations has been studied successively in the linear approximation,2) while Lifshitz's assumption was not always used. On the other hand, it has been assumed that an early stage of the UnIverse was very turbulent and density fluctuations were not small. S ) At the stage when radiation density was larger than matter density and matter was wholly ionized, matter was strongly kicked by photon particles and hindered from condensing. But, once matter was neutrarized, density fluctuations condensed promptly into bound systems. However, we do not know at present how quiet or turbulent the early stages were. Accordingly, still we could assume the existence of fluctuations with vari­ ous amplitudes. In the process of their condensation, gravitation would have played the main role, and, as the density contrasts increased to the order o£