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Seismic Frequency Component Inversion for Elastic Parameters and Maximum Inverse Quality Factor Driven by Attenuating Rock Physics Models

Surveys in Geophysics - Wed, 07/01/2020 - 00:00
Abstract

Attenuation exists in seismic wave propagation in subsurface layers, and relatively high attenuation occurs in oil-bearing reservoirs. Inversion of frequency components of observed seismic data generates values of attenuation factor 1/Q, which produces potential results for determining oil-bearing reservoirs. Beginning with expressions of seismic wave velocity in attenuating media, we involve P-wave maximum attenuation factor to rewrite P-wave velocity driven by an attenuating rock physics model, and we also employ an empirical relationship between P-wave attenuation factor and S-wave attenuation factor to express S-wave velocity in terms of P-wave maximum attenuation factor. Using the derived P- and S-wave velocities, we extend Zoeppritz equations to compute reflection coefficient for an interface separating two attenuating media. Under the assumption that contrasts in elastic properties of two media across the interface are small and the background attenuation is weak, we propose a linearized reflection coefficient of PP-wave as a function of contrasts in elastic parameters (i.e., P-wave velocity, S-wave velocity and density) and attenuation factor, and expression of elastic impedance (EI) is also presented. Based on the EI, we demonstrate an approach of estimating elastic parameters and attenuation factor from frequency components of partially incidence-stacked seismic data, which is implemented as a two-step inversion involving the prediction of EI datasets using a model-based damping least-squares algorithm and nonlinear inversion for elastic parameters and attenuation factor. Noisy synthetic seismic data generated using the extended Zoeppritz equations are employed to verify the robustness and stability of the proposed inversion approach. Applying the proposed approach to a real dataset acquired over an oil-bearing reservoir, we obtain convincing results of P-wave velocity, S-wave velocity, density and attenuation factor, which can reasonably match corresponding well log data.

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The Santa Fe Intrusion and Other Magmatic Bodies Under the Chichón Volcano Area (Mexico): Inferences from Aeromagnetic and New Petrologic-Geochronologic Data

Surveys in Geophysics - Wed, 07/01/2020 - 00:00
Abstract

We review the current knowledge of the Pleistocene Modern Chiapanecan Volcanic Arc (MCVA). This arc is related to the subduction of the Cocos plate beneath the North American plate in the State of Chiapas, southeastern Mexico. The MCVA consists of large intrusive bodies, domes, eroded volcanic landforms, and the active El Chichón, which produced the disastrous 1982 eruption, the deadliest in Mexico’s recorded history. The available geological knowledge, and new geological and aeromagnetic data on the arc, reveals a system composed of a sizeable intrusive body called the Santa Fe diorite, and small-size volcanoes such as El Chichón and Catedral, and extinct volcanoes associated with volcaniclastic deposits. A 3D-inversion of the aeromagnetic anomalies indicates that the Santa Fe diorite is a large intrusive body (27 km long, 4 km wide with a minimum volume of 1662 km3) while small volcanoes such as El Chichón have small-size magma chambers (~ 7 km3). Interestingly, our models of the causative bodies for the aeromagnetic anomalies suggest that the El Chichón volcano, as well as of other volcanic areas in the region, are not linked directly to the Santa Fe intrusive. However, new 40Ar/39Ar dates for samples from the Santa Fe intrusive (2.2 Ma), the Catedral volcano (1.6 Ma), and a mafic enclave (1.09 Ma) hosted in 1982 Chichón deposits, along with the aeromagnetic anomalies and geochemical data confirm that these extrusive and intrusive structures belong to the MCVA. The chemistry of these structures suggests that magmas generated in the upper mantle by the subduction system evolved through different processes, such as crustal contamination for the Santa Fe diorite and Catedral volcano, and crystal fractionation for El Chichón volcano.

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Forward Gravity Modelling to Augment High-Resolution Combined Gravity Field Models

Surveys in Geophysics - Wed, 07/01/2020 - 00:00
Abstract

During the last few years, the determination of high-resolution global gravity field has gained momentum due to high-accuracy satellite-derived observations and development of forward gravity modelling. Forward modelling computes the global gravitational field from mass distribution sources instead of actual gravity measurements and helps improving and complementing the medium to high-frequency components of the global gravity field models. In this study, we approximate the global gravity potential of the Earth’s upper crust based on ellipsoidal approximation and a mass layer concept. Such an approach has an advantage of spectral methods and also avoids possible instabilities due to the use of a sequence of thin ellipsoidal shells. Lateral density within these volumetric shells bounded by confocal lower and upper shell ellipsoids is used in the computation of the ellipsoidal harmonic coefficients which are then transformed into spherical harmonic coefficients on the Earth’s surface in the final step. The main outcome of this research is a spectral representation of the gravitatioal potential of the Earth’s upper crust, computed up to degree and order 3660 in terms of spherical harmonic coefficients (ROLI_EllApprox_SphN_3660). We evaluate our methodology by comparing this model with other similar forward models in the literature which show sub-cm agreement in terms of geoid undulations. Finally, EIGEN-6C4 is augmented by ROLI_EllApprox_SphN_3660 and the gravity field functionals computed from the expanded model which has about 5 km half-wavelength spatial resolution are compared w.r.t. ground-truth data in different regions worldwide. Our investigations show that the contribution of the topographic model increases the agreement up to ~ 20% in the gravity value comparisons.

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Analysis of Plasma Bubble Signatures in Total Electron Content Maps of the Low-Latitude Ionosphere: A Simplified Methodology

Surveys in Geophysics - Wed, 07/01/2020 - 00:00
Abstract

The ionosphere over the Brazilian region has particular characteristics due to the large geomagnetic declination angle over most of the territory. Furthermore, the equatorial ionization anomaly southern crest is located over the Brazilian territory. In this region, plasma irregularities may arise in the post-sunset hours. These ionospheric irregularities develop in the form of magnetic field-aligned plasma depletions, known as equatorial plasma bubbles, which may seriously affect radio signals that propagate through them. These irregularity structures can cause amplitude and phase scintillation of the propagating signals, thereby compromising the availability, performance, and integrity of satellite-based communication and navigation systems. Additionally, the total electron content (TEC) introduces propagation delays that can contribute to range measurement errors for global positioning system (GPS) users. The ionospheric characteristics change significantly according to the time of day, season, as well as the solar and geomagnetic activities, among other factors. Indeed, the ionosphere is one of the most significant sources of errors in the positioning and navigation systems based on the GPS satellites. Due to these features, there is a strong interest by the scientific community in better understanding and characterizing the ionospheric behavior. In this context, the TEC analysis has wide applicability for space plasma studies and is a well-established tool for investigating the ionospheric behavior and its potential impact on space-based navigation systems. One of the goals of these studies is the generation of TEC maps for a geographic region based on GPS observations. In the present work, some electrodynamic processes of the low-latitude ionosphere are reviewed and the TEC estimation based on GPS measurements is revisited in detail. A methodology aimed at creating the TEC maps is presented and validated by comparison with results from other geophysical instruments, such as all-sky imagers and ionosondes. Finally, examples of the ionospheric behavior displayed by TEC maps during equatorial plasma bubble events and a geomagnetic storm are fully described and discussed.

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Gravity Field Modeling Using Tesseroids with Variable Density in the Vertical Direction

Surveys in Geophysics - Wed, 07/01/2020 - 00:00
Abstract

We present an accurate method for the calculation of gravitational potential (GP), vector (GV), and gradient tensor (GGT) of a tesseroid, considering a density model in the form of a polynomial up to cubic order along the vertical direction. The method solves volume integral equations for the gravitational effects due to a tesseroid by the Gauss–Legendre quadrature rule. A two-dimensional adaptive subdivision technique, which automatically divides the tesseroids near the computation point into smaller elements, is applied to improve the computational accuracy. For those tesseroids having small vertical dimensions, an extension technique is additionally utilized to ensure acceptable accuracy, in particular for the evaluation of GV and GGT. Numerical experiments based on spherical shell models, for which analytical solutions exist, are implemented to test the accuracy of the method. The results demonstrate that the new method is capable of computing the gravitational effects of the tesseroids with various horizontal and vertical dimensions as well as density models, while the evaluation point can be on the surface of, near the surface of, outside the tesseroid, or even inside it (only suited for GP and GV). Thus, the method is attractive for many geodetic and geophysical applications on regional and global scales, including the computation of atmospheric effects for terrestrial and satellite usage. Finally, we apply this method for computing the topographic effects in the Himalaya region based on a given digital terrain model and the global atmospheric effects on the Earth’s surface by using three polynomial density models which are derived from the US Standard Atmosphere 1976.

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Recursive Analytical Formulae of Gravitational Fields and Gradient Tensors for Polyhedral Bodies with Polynomial Density Contrasts of Arbitrary Non-negative Integer Orders

Surveys in Geophysics - Wed, 07/01/2020 - 00:00
Abstract

Exact computation of the gravitational field and gravitational gradient tensor for a general mass body is a core routine to model the density structure of the Earth. In this study, we report on the existence of closed-form solutions of the gravitational potential, gravitational field and gravitational gradient tensor for a general polyhedral mass body with a polynomial density function of arbitrary non-negative integer orders that can simultaneously vary in both horizontal and vertical directions. Our closed-form solutions of the gravitational potential and the gravitational field are singularity-free, which implies that the observation sites can have arbitrary geometric relationships with polyhedral mass source bodies. However, weak logarithmic singularities exist on the edges of polyhedra for the gravitational gradient tensor. A simple prismatic mass body with polynomial density contrast varying in the vertical direction and a complicated dodecahedral mass body with quartic-order density contrasts were tested to verify the accuracy of the newly derived closed-form solutions. For the gravitational potential, gravitational fields and gradient tensors, our closed-form solutions are in excellent agreement with previously published analytical solutions and Gaussian numerical quadrature solutions.

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Correction to: Diffusion and Thermodiffusion of Atmospheric Neutral Gases: a Review

Surveys in Geophysics - Wed, 07/01/2020 - 00:00

The original version of this article unfortunately contained misprints. The corrections of these misprints are given below.

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Elastic Least-Squares Imaging in Tilted Transversely Isotropic Media for Multicomponent Land and Pressure Marine Data

Surveys in Geophysics - Wed, 07/01/2020 - 00:00
Abstract

Traditional elastic reverse-time migration (RTM) involves P-/S-wave separation for the source and receiver wavefields, followed by applying the zero-lag cross-correlation imaging condition to produce PP and PS images. In anisotropic media, P-/S-wave decomposition requires a higher memory and computational cost than that in isotropic media. In addition, finite acquisition apertures and band-limited source functions result in unsatisfactory resolutions and amplitudes. To mitigate these problems, we present an elastic least-squares imaging method for tilted transversely isotropic media and apply it to land multicomponent and marine pressure data. Unlike traditional RTM, we use the relative perturbations to the product of density and squared axial (compressional/shear) velocities as reflectivity models (\(\Delta \ln{C}_{33}\) and \(\Delta \ln{C}_{55}\)), and estimate them by solving a linear inverse problem. Numerical experiments illustrate that subsurface reflectors can be well resolved in adjoint images for land multicomponent data, because of the presence of both P- and S-waves in seismograms. Least-squares migration helps to further improve spatial resolution and image amplitudes. Since there are no direct S-waves in marine streamer data, adjoint RTM images of \(\Delta \ln{C}_{55}\) are mainly resolved with the converted S-waves and are not as good as those in \(\Delta \ln{C}_{33}\) images. By approximating the Hessian inverse, least-squares migration allows us to take advantage of the weak converted P–S–P-waves and improve the \(\Delta \ln{C}_{55}\) image quality. Numerical experiments for synthetic and field data demonstrate the feasibility and advantage of the proposed least-squares TTI RTM compared with wave-mode separation-based elastic RTM. In field data experiments, we observe that since there are no strong P–S–P converted waves in streamer pressure records from the marine survey, the reflectors in \(\Delta \ln{C}_{55}\) image might be mainly imaged from P-waves due to the amplitude versus offset (AVO) effects.

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Comparative analysis of local and global atmospheric electric field at the Northern Pakistan

Publication date: 15 September 2020

Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 206

Author(s): S.F. Gurmani, N. Ahmad, J. Tacza, T. Hussain, S. Shafaq, T. Iqbal

An effort to study the influence of tides on the longitudinal variation of vertical <strong>E</strong><math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" id="d1e786" altimg="si41.svg" class="math"><mo>×</mo></math><strong>B</strong> drif

Publication date: 15 September 2020

Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 206

Author(s): Valence Habyarimana, John Bosco Habarulema, Patrick Mungufeni, Jean Claude Uwamahoro

Modeling Diurnal Land Surface Temperature on a Local Scale of an Arid Environment Using Artificial Neural Network (ANN) and Time Series of Landsat-8 Derived Spectral Indexes

Publication date: 15 September 2020

Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 206

Author(s): Aliihsan Sekertekin, Niyazi Arslan, Mehmet Bilgili

Gravity wave activity in the middle atmosphere from SATI airglow observations at northern mid-latitude: Seasonal variation and comparison with tidal and planetary wave-like activity

Publication date: Available online 2 June 2020

Source: Journal of Atmospheric and Solar-Terrestrial Physics

Author(s): M.J. López-González, M. García-Comas, E. Rodríguez, M. López-Puertas, I. Olivares, J.M. Jerónimo-Zafra, N.F. Robles-Muñoz, T. Pérez-Silvente, M.G. Shepherd, G.G. Shepherd, S. Sargoytchev

Comparison and evaluation of a bottom-up GPS-RO electron density retrieval for D and E regions using radar observations and models

Publication date: Available online 1 June 2020

Source: Journal of Atmospheric and Solar-Terrestrial Physics

Author(s): N. Swarnalingam, D. Wu, D.R. Themens

On the necessity of using <em>foμEs</em> instead of <em>foEs</em> in estimating the intensity and variability of sporadic E layers

Publication date: 15 September 2020

Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 206

Author(s): Christos Haldoupis, Haris Haralambous, Chris Meek

Westward propagation of substorm by THEMIS and ground-based observations

Publication date: 15 September 2020

Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 206

Author(s): I.V. Despirak, T.V. Kozelova, B.V. Kozelov, A.A. Lubchich

Comparisons and evaluation of aerosol burden and optical depth in CMIP5 simulations over East Asia

Publication date: 15 September 2020

Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 206

Author(s): Ruolin Li, Xiaoyan Ma, Feilin Xiong, Hailing Jia, Tong Sha, Rong Tian

A catalog of prominence eruptions detected automatically in the SDO/AIA 304 Å images

Publication date: 1 September 2020

Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 205

Author(s): S. Yashiro, N. Gopalswamy, S. Akiyama, P.A. Mӓkelӓ

Tidal influence in the determination of long-term trends in the mesosphere-lower thermosphere from LIDAR observations

Publication date: 15 September 2020

Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 206

Author(s): David A. Krueger, Chiao-Yao She, Jens Oberheide

Day-to-day variability of the bottomside ionosphere

Publication date: 1 September 2020

Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 205

Author(s): Kate A. Zawdie, Manbharat S. Dhadly, Sarah E. McDonald, Fabrizio Sassi, Clayton Coker, Douglas P. Drob

Atmospheric phase screen estimation for land subsidence evaluation by InSAR time series analysis in Kurdistan, Iran

Publication date: 1 September 2020

Source: Journal of Atmospheric and Solar-Terrestrial Physics, Volume 205

Author(s): Saeid Haji-Aghajany, Yazdan Amerian

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