Acta Geodaetica et Geophysica最新文献

Amplitude Versus Offset (AVO) analysis has been successfully applied in the hydrocarbon industry for more than three decades. This effective tool of the joint seismic and well-log data processing enables to predict and analyze fluid saturated porous geological formations. AVO methodology is based on the anomalous behavior of the pre-stack reflected amplitudes observed from fluid bearing rocks. However, the potential of AVO methodology is still unexploited in geothermal exploration, although the lithology and rock physical properties are very similar. In this study, we summarize the theoretical backgrounds and calculate synthetic AVO responses of a known geothermal reservoir located in the fractured carbonates of the Mesozoic basement. We demonstrate that the AVO response of a deep geothermal reservoir can be quite different from the amplitude response observed from a hydrocarbon bearing clastic formation. AVO attributes of the investigated geothermal reservoir are presented, and the potential of its detection by seismic amplitude data are discussed.

Aseismic dip-slip normal fault displacement related to numerous fast-slipping active faults was recently observed in several localities in the western Anatolia extensional province. Still, the characteristics of displacements along with the behavior of individual fault segments are poorly known. Here we analyze an aseismically active normal fault affecting the settlement area of the Sarıgöl district, Turkey, at the surface rupture area of the 1969 magnitude 6.5 Alaşehir earthquake. A precise leveling method was implemented in this area between July 2017 and 2020, to determine the vertical movements of the hanging wall relative to the footwall of the Sarıgöl fault. The yearly vertical movement on the surface along Profile 1 was − 7.0, − 7.3, and − 7.0 cm, respectively, for the three years starting in July 2017, and on Profile 2 it was − 7.7, − 8.7, and − 7.8 cm for the same time period. This persistent deformation, especially in the summer and fall seasons, suggests that may be related to groundwater level changes. Intensive agriculture is conducted in the region and a high level of irrigation activity in the summer period causes a decrease in groundwater levels. In addition, the continued deformation together with intensive precipitation in winter and spring despite high groundwater levels leads to the idea that tectonic creep movement could be a second reason for the deformation in the area. In the current study, the most important result is that the aseismic deformation starting after the 1969 Mw6.5 Alaşehir earthquake still continues rapidly today with a velocity of 70–80 mm/year down-dip. This indicates that the damage zone of the Sarıgöl fault is not appropriate for settlements in the Sarıgöl district due to continuous high amounts of vertical displacement, and that appropriate building policy and awareness campaigns are needed.

Multipath effect is a main source of error in relative positioning, which cannot be eliminated or mitigated by differential algorithm. We discuss the topic of mitigating multipath at a static station in observation domain with GPS and BDS systems. At present, the sidereal filtering as one of the most commonly used multipath mitigating methods relies on the repetition period of multipath, which cannot be accurately estimated influenced by the maneuver of satellite orbit and the time interval of satellite ephemeris. The window matching method as a real-time method was proposed to reduce this effect. However, this method is affected by similarity measures in the process of real-time window matching. We propose a near real-time window matching method based on sidereal filtering. In the modified method, the satellite single difference residual is divided into segments and the cross-correlation method is used to obtain the multipath repeat time. At the same time, the second segment series overlaps with the previous segment to ensure a near real-time performance. Based on the obtained repeat time, the template window and matched window are formed by epochs in the segment and then an affine transformation is applied to determine the value of multipath correction between the two windows. Tests were conducted for GPS and BDS systems respectively using the baseline observations at static stations in the Ha-Jia high-speed railway. The experimental results show that the modified method can mitigate the multipath error in double difference observation, and finally provide higher positioning results than methods without model and traditional model. In practice, application of the modified method in near real-time baseline positioning can effectively mitigate the multipath error.

Liquid nitrogen (LN₂) ultra-low temperature fracturing presents a broad application range for geothermal energy development. Therefore, studying the effect of LN₂ cooling on the pore characteristics of high-temperature limestone is critical. In this study, Rizhao limestone obtained from Shandong Province was selected as the test object and subjected to heat treatment at different temperatures (25–600 °C) to investigate the changes in the pore characteristics of limestone after rapid LN₂ cooling based on nuclear magnetic resonance. The total porosity of limestone continuously increases due to the continuous expansion of original fractures in the limestone and the generation of new fractures caused by thermal stress resulting from high temperatures and the rapid LN₂ cooling. For heat treatment of 600 °C, no high amplitude is observed in the damage process. The fractal dimension of permeable pores (D_P) initially decreases and then increases with an increase in the quenching temperature difference, and the fractal dimension of total pores (D_T) shows a general decreasing trend. The compressive strength increases with an increase in D_T. Acoustic emission (AE) technology was used to monitor the deformation and failure of rocks. The low amplitude of AE is mainly distributed in the low-frequency band.

We show in this note a simple exercise to overcome a common preconception among Geodesy students about the “best” reference ellipsoid. This helps students to overcome their previous ideas based on a purely geometric vision of the reference ellipsoids and advance to a more physical point of view, where the Earth’s gravity plays a fundamental role.

We analyze theoretically ultra-low frequency electromagnetic noise caused by deformations of seabed and porous coastal rocks subjected to incident long oceanic waves. A variable pressure on the seabed due to propagation of long gravity waves (LGWs) gives rise to variations in pore pressure gradient followed by groundwater filtration in pores and channels of porous rocks. These processes result in the generation of telluric electric currents in water-saturated porous rock of the seashore due to electrokinetic effect. In the model a displacement of the sea surface in LGWs is described in the "shallow water" approximation. A set of basic equations describing rock strain and electrokinetic effect is solved in quasi-static approximation. The telluric electric field in the porous rocks of coastal zone are found as a function of depth and distance to the coastline at different frequencies of LGWs. The theoretical analysis has shown that telluric electric noise produced by the LGW can exceed the level of natural electric noise during geomagnetically quiet period in a coastal strip about several tens of meters.

The present paper introduces a Legendre polynomials based interval inversion method for processing multi-borehole logging data. The method allows the determination of lateral changes of the layer-thicknesses together with the vertical and lateral variations of petrophysical parameters along a 2D cross-section of several boreholes. The method is assessed using noisy synthetic measurements of a petrophysical model made of two-layers structure related to hydrocarbon bearing formations. The numerical experiments aided to investigate the stability and convergence of the 2D interval inversion procedure. To ensure the accuracy and reliability of the inversion results, the misfit of data and model distance are tested, beside the calculation of estimation errors and correlation coefficients. A large amount of input data relative to the number of unknowns results in a high overdetermined ratio, consequently more precise estimates are obtained in stable and convergent procedure than in conventional local (1D) inversion schemes. The feasibility of the 2D interval inversion method is shown by analysing in-situ well logging data acquired in four wells situated in an Egyptian hydrocarbon field.

Works on establishment of the spirit levelling network in the Balkan countries were ruled by the political and economic circumstances. This was subject to the analysis since the Austro-Hungarian Monarchy period, over former Yugoslavia in all of its political forms, down to the present countries of the Balkan Peninsula. Heights differences and heights are part of the II Levelling Network of High Accuracy (II.NVT network). The works on establishment of II.NVT network have been organized and performed by the Federal Geodetic Administration of former Yugoslavia and the Geodetic Administrations of the accompanying Republics. The Military-Geographic Institute from Belgrade had performed gravity measurements over one part of the levelling network. “The II.NVT network data are the subject of computer processing, modern analyses, fundamental and applied scientific researches and application in solving some practical tasks” (Rožić in Acta Geodaetica et Geophysica Hungarica 36(2):231–243, 2001). Calculations of accuracy of corrections in different height systems will be presented in this paper. The subject of this analysis is the error sources in the corrections for the orthometric, normal, and normal orthometric heights. The error sources that accompany the spirit levelling procedure are, for the most part, examined with the assumption that the height difference may be determined with the accuracy of 1.0 mm/km. The corrections in different height systems will be made through the function of a link to the directly/indirectly measured values. The accuracy of the correction will be presented by applying the law of error propagation on the data collected in the II.NVT network for the territory with the characteristic relief. The reason for writing this paper is noted deviation from theoretical assumptions on the shape of reference surfaces in the various height systems. The deviation noted are in the part of relief characteristic over the deep karst and high mountains in one polygon of the II.NVT network, over the distance of 40 km.

Geoelectric surveys are among popular subsurface geophysical imaging techniques that provide significant insights into the electrical properties of subsurface targets. In this research, geoelectric modeling of travertine deposits at the Atashkohe region in Iran is performed through discretizing the physical model domain through structured (quadrilateral) and unstructured (triangular) meshes. This meshing tool captures the accurate borders of a rugged topography area along with any complex-shaped travertine sources. The modeling process was accomplished through utilizing an open-source python-based software called “ResIPy”, which handles all processing steps necessary for reliable forward and inversion of geoelectrical data (i.e., electrical resistivity and induced polarization). Three synthetic electrical models according to the geological background of the studied area were simulated to examine the efficiency of the 2D electrical survey in imaging the travertine building stone. Two types of structured and unstructured meshing were designed to cope with the rough topography surface and any intricate geometry of subsurface target. The inversion results of the synthetic models approved the accuracy and efficiency of both geoelectrical survey and data modeling in travertine exploration. Finally, as a case study, tomography data of electrical resistivity and chargeability taken from the Atashkohe travertine mine were geophysically modeled to infer geological sections along three 2D profiles surveyed in the region. Data were collected with an electrode spacing of 15 or 10 m through a combination of dipole-dipole and pole-dipole arrays. The results of inverse modeling indicated that the provided geological and electrical sections at depth could be related to travertine lenses and further survey can help delineation of these building rocks. Comparison of electrical models and stratigraphic column obtained from two drillings along one profile showed a relatively good agreement as well.

The Aegean is tectonically the most active and complex area in the Mediterranean region, including numerous active structures of all types of kinematics, often related to destructive seismic events. In such a tectonic environment, the estimation of rotational regime is decisive in the determination of the geodynamic and geotectonic evolution of this region. Satellite geodesy is a reliable way of estimating the rotation rate, while its comparison with palaeomagnetic data can lead to the identification of well-established patterns. To this direction, we use geodetic datasets recorded by permanent GPS/GNSS stations and we apply the triangulation methodology by combining three stations each time. Consequently, for each and every point of the 4733 extracted ones, the rotation rate and its pattern are calculated. Using the above results, two rotation models are proposed: one for the past 1 Myr and one for the past 5 Myr. In addition, the geostatistical analysis of the geodetically extracted results was carried out, in order to determine their spatial distribution. The comparison and combination of these two geodetically induced models with palaeomagnetic data, led to the delineation of distinct upper crust areas of uniform rotation within the Aegean region.