A study of the Earth's crust near Gauribidanur in Southern India

1971 ◽  
Vol 61 (3) ◽  
pp. 671-683
Author(s):  
S. K. Arora

abstract A hypothetical two-layered model has been evolved for the Earth's crust near Gauribidanur. The model is found to be consistent with the local earthquake and rockburst data obtained at Gauribidanur seismographic array. Sixty-seven well-recorded seismic events have been studied for this purpose. First arrival conditions for some of the phases in a “near-source” (epicentral distance Δ ≦ 10°) seismogram have been derived and subsequently made use of in establishing the nature of the first arriving phases pertaining to the available data. Thickness of the top granitic layer and the depth of Moho below this layer are found to be about 16 km and 19 km, respectively. Observed velocities are 5.67, 6.51 and 7.98 km/sec for P phases, and 3.46, 3.96 and 4.61 km/sec for the corresponding S phases. Values of the crustal parameters given by this study have been used in estimating the relative differences in travel times corresponding to various observed phases. These travel times may improve the precision with which earthquakes in this region could be located. Typical geographical and geological features of the region are also briefly described.

1970 ◽  
Vol 60 (6) ◽  
pp. 1921-1935
Author(s):  
B. M. Gurbuz

Abstract The aim of this paper is to investigate the velocity distribution and structure of the Earth's crust and upper mantle from the close collaboration of theory and experimental results of travel times and spectrum characteristics of body waves. The interpretation was based on 38 seismic records which were obtained from the “Project Early Rise” experiment during July 1966. The results refer to the area bounded by latitudes 49°W and 51°30′ and longitudes 93°W and 98°W. A least-squares analysis of the travel-time data was made and the uncertainties of the slopes, intercept times, and corresponding velocities were determined. The observed wide-angle reflections were used to calculate the root mean square velocities applying the T2 - X2 method. Depth calculations for the velocity discontinuities and seismic depth contour maps were made. A model was constructed, and the validity of the proposed new model was tested by comparing the observed travel times, spectrum-amplitude ratios, and relative phase shifts of body waves with theoretically expected values. Evidence is given for three discontinuities in the Earth's crust with velocities of 6.11 ± 0.01 km/sec, 6.8 ± 0.08 km/sec, and 7.10 ± 0.04 km/sec at average depths 18 ± 2 km and 25.5 ± 0.9 km. Velocities in the uppermost part of the mantle were determined as 7.90 ± 0.05 km/sec and 8.48 ± 0.05 km/sec with interfaces at the average depths of 34 ± 1 km, and 47 ± 1 km, respectively.


2018 ◽  
Vol 56 ◽  
pp. 04019
Author(s):  
Nikolay Grib ◽  
Valery Imaev ◽  
Galina Grib ◽  
Lyudmila Imaeva ◽  
Igor Kolodeznikov

Impulse loads, arising due to the high natural seismicity of the South Yakutia region, exercise both direct and indirect effects on the upper part of the Earth's crust during industrial explosions. The direct effects result from nonlinear displacements caused by the blast wave and the subsequent formation of new disturbances. The indirect effects arise due to the activation of structural elements along geological contacts, leading to the emergence of technogenic seismicity foci. The foci of induced seismicity are either confined to the blast points, or located along the tectonic structures crossing quarry fields. The technogenic impact on the geological environment transforms the independent local seismic process, since explosions trigger a chain of local seismic events. The near-surface layers of the Earth's crust become activated in the area of dynamic influence of active faults. Under the influence of explosions, both the number of seismic events and the average level of released energy alter. Impulse loads on the geological environment lead to a spatial redistribution of the foci of low-energy (K <7) earthquakes. The main form of the geodynamic development of seismogenic faults is the movement of their sides in the form of mutual “slippage”. Seismic events are manifested only when the aforementioned form of deformation is impossible or difficult to develop, in other words, when the stress-state areas of the Earth's crust develop. Therefore, the shaking impact of blasts can be considered as a factor contributing to the predominance of aseismic forms of fault motion in the form of smooth slippage of their sides. In conclusion, the impact of industrial blasts can not only activate faults around the mining area, but also have an unloading effect on the foci of seismic hazard forming in the interior, i.e. the redistribution of earthquake energy in terms of reducing earthquake energy class.


2017 ◽  
Vol 50 (3) ◽  
pp. 1545 ◽  
Author(s):  
S. Bitharis ◽  
A. Fotiou ◽  
C. Pikridas ◽  
D. Rossikopoulos ◽  
S. Pavlides ◽  
...  

The contribution of GPS networks in monitoring seismic events is important because they can provide a direct geometrical information on the Earth's crust using satellite observations In this study position displacements of permanent GPS stations are determined due to intense seismic events in the North Aegean area after the strong earthquake on May 24, 2014. The horizontal coseismic displacements for the Samothrace Island were estimated at 9.4 cm and for Lemnos Island at 5.2 cm respectively. A study period of seven days was enough to show that the deformation evolved into two days.


Author(s):  
Romela Pashayan ◽  
Levon Harutyunyan ◽  
Kristina Tovmasyan

The geodynamics of the earth’s crust in the territory of Armenia is given according to seismic data, deformographic measurements, hydro geodynamic observations of the groundwater level, and geochemistry of mineral waters in the central part of the region. The map of the epicenters of earthquakes over the past three years includes stressed sections (concentration of earthquake epicenters) of the earth’s crust with increased activity geodynamic processes. Based on the results of the registration of deformations of two directions, the values of areal, volumetric, and vertical deformations are calculated. Variations in the water level in hydro geodynamic wells were obtained due to seismic events; the amplitudes of the variations depend on the magnitude of the earthquake, the distance from the epicenter, and the magnitude of the calculated deformation of the earth’s crust. The main components of the chemical composition of mineral waters (CL, HCO3, SO4, Mg), gas - CO2, and Ph in comparison with seismicity and other geodynamic processes of the earth’s crust.


Author(s):  
Gurban Yetirmishli ◽  
Sabina Kazimova

The methodology of the converted waves, or as it is commonly called, the "Receiver function" method, is well known and is widely used throughout the world to study the deep structure of the Earth up to 800 km. The method is based on the registration and interpretation of converted Ps waves. These studies were carried out as part of the International Seismotomo-graphic Laboratory using a software package developed at the University of Missouri (USA). One of the best regions for studying the early stages of mountain building is the Greater Caucasus, where most of the volcanism and mountain building appears to be 5 million years. Of particular interest is the immersion zone of the Kura Basin beneath the Greater Caucasus, the so-called subduction zone, which has not been sufficiently studied to date. To this end, we began our studies of the depth of the Moho border with this region. Thus, for the first time on the basis of the analysis of the wave characteristics of distant earthquakes recorded at seismic and telemetric stations of the RSSC, within the framework of the international project "Transect", the depths of the Moho border for the Azerbaijan part of the Greater Caucasus were refined by the method of exchange reflected Ps waves ("Receiver function"). Seismo-grams of the selected earthquakes were processed using the Seismic Analysis Code (SAC) software package under the MacOs operating system. The study examined seismological data recorded by a network of telemetry stations (N=20) for 2009-2019. In total, 2428 earth-quakes recorded at an epicenter distance of 35 to 90 degrees were analyzed. At the first stage, frequency filtering was carried out in order to eliminate oscillations that were too high, containing the effects of random scattering on inhomogeneities, and too low frequencies that re-duce the resolution. The working range of the periods ranged from two to 10 seconds. Next, two-dimensional and three-dimensional rotation of the axes was carried out. The summation of all traces was carried out with time shifts relative to some reference epicentral distance, which is assumed to be 60 degrees. On the summarized Q-tracks of the receiving functions, the Moho boundary with a delay time of 4.0 sec is clearly distinguished. Thus, a map of iso-lines of the depths of the Moho surface was constructed and depths were determined for the territory of the Guba-Gusar region 48-50 km, the Zagatala-Balakan region 46-47 km, the Shamakhi-Ismayilli region 48-52 km. As it was said earlier, the first definitions of the depth of the surface of Moho in Azerbaijan were made based on the data from the state earthquake and the gravitational model of the Earth's crust. R.M. Gadzhiev in 1965 and E.Sh. Shikhalibeyli in 1996 built such models. The data obtained are consistent with the available data, but discrepancies have been received. Compared with the map constructed according to the GSZ-KMPV and gravimetric data by R.M. Gadzhiev (1965), the difference in the thickness of the earth's crust was from one to 15 km. Compared with the map constructed according to the FGP and gravimetric data by E.Sh Shikhalibeyli (1996), the difference in the thickness of the earth's crust varied from one to 10 km.


2021 ◽  
Vol 254 ◽  
pp. 02003
Author(s):  
Elena Bataleva

The paper presents the results of experiments carried out at the regime points of magnetotelluric monitoring both on the territory of the Bishkek geodynamic test site (Northern Tien Shan) and on a series of monitoring profiles in various geological conditions. Previous studies indicate the relationship of variations in the electromagnetic and seismic fields, lunisolar tidal effects, seismic regime with the processes of fracturing. The purpose of this work is to establish the features of the relationship between the spatio-temporal distribution of seismicity and the distribution of geoelectric inhomogeneities in the Earth’s crust (fault-block tectonics of the region). Based on the analysis of the results of the interpretation of magnetotelluric data (2D inversion) and new detailed seismotomographic constructions, the verification of geoelectric models was carried out, the analysis of the distribution of hypocenters of seismic events was carried out. Special attention was paid to the confinement of earthquakes to listric fault structures. The relationship between the distribution of the hypocenters of seismic events and the spatial position of the electrical conductivity anomalies is confirmed by the authors explanation of the physical nature of the identified conducting structures, based on hypotheses of fluidization and partial melt of the Earth’s crust.


Author(s):  
S.E. Kazimova

In the last decade, significant advances have been made in the theory and application of seismic tomography. These include refinements in model parameterization, 3D ray tracing, an inversion algorithm, sharing local, regional, and teleseismic data, and adding transformed and reflected waves to tomographic inversion. Explorations have shown that with the help of seismotomography it is possible to obtain reliable data on the deep structure of the Earth, its thickness, the mutual arrangement of layers, as well as tectonic structures identified in the earth’s crust. Due to a significant increase in the number of seismic stations in the Republican Seismic Survey Center and equipping them with modern instruments of the MacOs system (made by “Kinemetrics”), it was possible to obtain a large volume of observed seismic material and solve rather complex methodological issues, which is relevant today. The aim of this article is to redefine the data of the hypocenters of earthquakes that occurred on the territory of Azerbaijan for the period 2010‑2019 (ml>2.0) and calculate the velocity model of the earth’s crust using algorithms that are not included in the mandatory processing when compiling a catalog of seismic events. The catalog data were taken from the “Bureau of Earthquake Research” of the Republican Seismic Survey Centerof Azerbaijan National Academy of Sciences. Research methods. Within the framework of present work, using the double difference method, we redefined the location of seismic events, showing that the obtained positions of the epicenters are lined up in systems of linear chainsalong the main and feathering faults, which is consistent with the relief and geological concepts. Results. Comparing the values of the velocities with the values of the one-dimensional velocity model, it was found that at depths of 5‑10 km, there is good convergence in the regions of the Greater Caucasus. The middle Kura depression is mainly characterized by low velocities compared to the one-dimensional velocity model. At a depth of 15 km, the eastern part of the Middle Kura depression is characterized by good convergence, but in the western part high velocities are noted. The maximum convergence of velocities was noted at a depth of 35 km В последнее десятилетие были достигнуты значительные успехи в теории и применении сейсмотомографии. К ним относятся уточнения в параметризации модели, трас- сировка трехмерных лучей, алгоритм инверсии, совместное использование локальных, региональных и телесейсмических данных, а также добавление преобразованных и отраженных волн в томографическую инверсию. Исследования показали, что с помощью сейсмотомографии можно получить достоверные дан- ные о глубинном строении Земли, ее толщине, взаимном расположении слоев, а также о тектонических структурах, выявленных в земной коре. Благодаря значительному увеличению числа сейсмических стан- ций в РЦСС, оснащению их современными приборами системы MacOs (фирсы «Кинеметрикс»), удалось получить большой объем наблюденного сейсмического материала и решить довольно сложные методи- ческие вопросы, что является актуальным на сегодняшний день. Целью данной статьи является пере- определение данных гипоцентров землетрясений произошедших на территории Азербайджана за период 2010‑2019 гг. (ml>2,0) и вычислению скоростной модели земной коры с использованием алгоритмов, не входящих в обязательную обработку при составлении каталога сейсмических событий. Данные каталога были взяты в «Бюро исследований землетрясений» РЦСС при НАНА. Методы исследования. В рамках дан- ной работы методом двойных разностей мы переопределили положения сейсмических событий, показав, что полученные положения эпицентров выстраиваются в системы линейных цепочек, положение которых согласуется с рельефом и геологическими представлениями, располагаясь вдоль главного и оперяющих разломов. Результаты работы. Сопоставляя значения скоростей со значениями одномерной скоростной модели, установлено что на глубинах 5‑10 км наблюдается хорошая сходимость в областях Большого Кавказа. Среднекуринская депрессия в основном характеризуется малыми скоростями по сравнению с одномерной скоростной моделью. На глубине 15 км восточная часть Среднекуринской депрессии характе- ризуется хорошей сходимостью, однако в западной части отмечены завышенные скорости. Максимальная сходимость скоростей отмечена на глубине 35 км


1972 ◽  
Vol 9 (4) ◽  
pp. 339-352 ◽  
Author(s):  
Maurice K. Seguin

The author completely reviews previous geophysical work related to the nature and structure of the earth's crust in Fennoscandia. He explains the analytical procedure used for the seismic data and the method used to locate seismic events in Fennoscandia. Having described the method of analysis, the procedure for the calculation of the velocity of the seismic waves, and the location of seismic events which originate from Fennoscandia as well as the characteristics of the seismic waves registered, the author calculates the thickness of 3 layers which constitute the earth's crust at various localities in Fennoscandia and drafts a spatial distribution for the thickness of each of these layers. The first order variations, which agree with the relative thickness of the layers, indicate the presence of a generally east-west gradient. A general thinning of the crust was observed to the west in Fennoscandia. In view of the results obtained, the author draws conclusions relative to the tectonic activity and the global geodynamics in Fennoscandia.


1968 ◽  
Vol 5 (4) ◽  
pp. 1037-1043 ◽  
Author(s):  
Yu. P. Neprochnov

Comparison of crustal structure of the deep basins of the Caspian, Black, and Mediterranean Seas indicates the similarities of the main characteristics: great Bouger anomalies, the absence of a 'granitic' layer, a thick sedimentary layer with a relatively smooth interface, aseismicity. However, each of the above-mentioned basins (or even different parts of one deep basin) has its peculiarities, which indicates a very complicated tectonic development of the entire Caspian–Mediterranean zone.


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