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1.
Self-potential anomalies with unexplained high values have been observed in various places. Such anomalies were reported in Peru more than 30 years ago. An explanation is proposed based on the electrokinetic effect obtained when a topographic high occurs above a rock layer through which water filtrates and which itself lies over a highly resistive layer. In such a case a fairly high self-potential may occur. Conversely, when one of these conditions is not met, the self-potential anomaly at the earth's surface resulting from the electrokinetic effect is strongly attenuated. 相似文献
2.
震前电磁场和大地自电位的异常是重要的地震前兆现象．在零磁空间对超低频段的磁场和自电位的变化进行了岩石破裂的实验研究，细致地揭示出电场、磁场出现异常变化的全过程，对深入认识超低频电磁信号的微观机理具有重要的意义．实验发现，岩石受力后应变、电位和磁场的缓慢变化在空间分布上是首先在近破裂源处出现，继而随裂纹的发展而改变位置；在时间序列上先出现自电位异常，然后是超低频磁场的变化；在异常形态上，超低频电磁信号呈现出早期、中期、晚期3个阶段的明显差异．研究表明，岩石微破裂引起裂隙尖端处的电荷分离. 静电荷在局部区域的积累和运移，导致了自电位的脉冲状变化；而在主破裂阶段，积累电荷的急速运动形成瞬间电流，激发了脉冲式的磁场异常．本文详细介绍了这一综合实验的技术步骤和观测结果，并对地震电磁前兆的微观机理进行了探讨． 相似文献
3.
The anomalies of electric-magnetic field and self-potential before earthquakes are important precursory phenom-ena.A simulating experiment study on the variations in ultra-low frequency(ULF)magnetic field and self-poten-tial during rock cracking was carried out in a magnetic field-free space.The results revealing in detail the whole process of the occurrences of electric and magnetic anomalises are significant for understanding the microscopic mechanism of ULF electric and magnetic signals.The experiment indicated that at the initial stage the slow changes in strain.self-potential and magnetic field with small amounts appeared firstly near the source of initial cracking,and then extended as the crack developed on.In the time domain,the self-potential anomaly emerged first and ULF magnetic field changes arose then.The shape of the ULF electric and magnetic anomaly varied ob-viously in early-,mid-and late-term of the test.The authors attributed the pulse-like changes of self-potential to the generationj and movement of the accumulated electric charges during the cracking caused by charge separation on the crack tips within the sample.While the magnetic pulses of shorter-period at the last stage of the test,may be induced by instantaneous electric current of the accumulated charege during the cracking acceleration.The technical method and the observational results of this experiment are given in detail and the microscopic mechanism of elec-tric and magnetic precursors before earthquake are discussd in the present paper as well. 相似文献
4.
Common studies on the static electric field distribution over a conductivity anomaly use the self-potential method. However, this method is time consuming and requires nonpolarizable electrodes to be placed in the ground. Moreover, the information gained by this method is restricted to the horizontal variations of the electric field. To overcome the limitation in the self-potential technique, we conducted a field experiment using a non conventional technique to assess the static electric field over a conductivity anomaly. We use two metallic potential probes arranged on an insulated boom with a separation of 126 cm. When placed into the electric field of the free air, a surface charge will be induced on each probe trying to equalize with the potential of the surrounding atmosphere. The use of a plasma source at both probes facilitated continuous and quicker measurement of the electric field in the air. The present study shows first experimental measurements with a modified potential probe technique (MPP) along a 600-meter-long transect to demonstrate the general feasibility of this method for studying the static electric field distribution over shallow conductivity anomalies.Field measurements were carried out on a test site on top of the Bramsche Massif near Osnabrück (Northwest Germany) to benefit from a variety of available near surface data over an almost vertical conductivity anomaly. High resolution self-potential data served in a numerical analysis to estimate the expected individual components of the electric field vector.During the experiment we found more anomalies in the vertical and horizontal components of the electric field than self-potential anomalies. These contrasting findings are successfully cross-validated with conventional near surface geophysical methods. Among these methods, we used self-potential, radiomagnetotelluric, electric resistivity tomography and induced polarization data to derive 2D conductivity models of the subsurface in order to infer the geometrical properties and the origin of the conductivity anomaly in the survey area. The presented study demonstrates the feasibility of electric field measurements in free air to detect and study near surface conductivity anomalies. Variations in Ez correlate well with the conductivity distribution obtained from resistivity methods. Compared to the self-potential technique, continuously free air measurements of the electric field are more rapid and of better lateral resolution combined with the unique ability to analyze vertical components of the electric field which are of particular importance to detect lateral conductivity contrasts. Mapping Ez in free air is a good tool to precisely map lateral changes of the electric field distribution in areas where SP generation fails. MPP offers interesting application in other geophysical techniques e.g. in time domain electromagnetics, DC and IP.With this method we were able to reveal a ca. 150 m broad zone of enhanced electric field strength. 相似文献
5.
将线性反演理论与正则化法相结合，提出一个火山地区二维自然电位（ＳＰ）异常反演方法．地下岩浆活动（对流体）是引起自电异常的极化源，反演的目的是计算地下视极化强度分布和极化源中心位置．可以通过用已知的各种资料改变地下极化源区域（简称源区）的方式来进行多次反演，以便获得一个比较合理的地下视极化强度分布模型．最后，分别给出意大利和墨西哥的两个火山地区的自然电位异常分析结果． 相似文献
6.
《Journal of Geodynamics》2003,35(1-2):209-220
The occurrence of swarm earthquakes in the Vogtland/NW-Bohemia area results probably from the physical interactions of fluids, the stress field and the geometry of the geological units. Therefore the present study aims at the development of a 3-D density model of the region with a vertical range of 35 km. A new Bouguer anomaly map is presented containing about 17 000 gravity data points. Prominent Bouguer anomalies are produced by the granites of Eibenstock and Karlovy Vary (low with −75 mGal), the metabasites near Mariánzké Lázně (high with 5 mGal) and the Münchberg Gneiss Massif (gravity high of Hof with 10 mGal). The geometry of the internal model structures correspond to geological units and, thus, the modelled gravity fits well the observed Bouguer anomaly. The 3-D gravimetric modellings indicate detailed geometries of the geological settings. With regard to the periodic occurrence of swarm earthquakes in the Vogtland region the existence of an upwelling mantle or a magmatic body is investigated. Precise information only can be given, if the vertical extension of the near surface bodies is known. 相似文献
7.
《Journal of Volcanology and Geothermal Research》2005,143(4):259-277
We conducted self-potential (SP) surveys sequentially from part to part over the central cones of Aso volcano since August 1998 by December 2001. The compiled SP map revealed large SP anomalies on the central cones. The main feature of the SP map is a ‘W-shaped’ profile along the NS-transect over the central cones. It is probable that this characteristic SP profile is produced by the combination of hydrothermal upwelling in the middle and topographic effect. A positive anomaly showing a large concentric pattern has appeared after correcting the topographic effect.To evaluate this SP anomaly, we implemented a numerical code that calculates electric potential produced by arbitrarily positioned current sources and sinks in any three-dimensional resistivity structure. A layered structure obtained from a time-domain electromagnetic (TDEM) field experiment was used for the resistivity model. The estimated current source is 300 A, being located in a conductive layer around the sea level. Meanwhile, sinks were estimated to sit on a circular area corresponding to the marginal part of the conductive layer.Water and heat budget study gives a lower limit of water mass transfer from depth to the bottom of the crater lake of Nakadake. This value was used to estimate the equivalent current in either case of electro-kinetic (EK) [Mizutani, H., Ishido, T., 1976. A new interpretation of magnetic field variation associated with the Matsushiro earthquakes, J. Geomag. Geoelectr., 28, 179–188.] or rapid fluid disruption (RFD) process [Johnston, M.J.S., Byerlee, J.D., Lockner, D., 2001. Rapid fluid disruption: A source for self-potential anomalies on volcanoes, J. Geophys. Res. 106(B3), 4327-4335.]. This comparison suggests that the former process is preferable to explain the observed SP anomaly. From these results we infer a large-scale hydrothermal system beneath the central cones of Aso volcano, in which the fluid flow initiates from the surrounding area, converging to the central vent to transport the heat and materials up to the crater lake of Nakadake through a vapor-filled conduit. 相似文献
8.
9.
Summary A quantitative method of interpreting self-potential anomaly caused by a spherical ore body using downward continuation method is presented. Master curves to determine the depth, radius and angle of polarization have been prepared. 相似文献
10.
Integrated geophysical surveys using vertical electrical sounding (VES), very low frequency (VLF) EM, radiation counting,
total magnetic field and self-potential (SP) measurements are carried out to characterize the geothermal area around a hot
spring in the Nayagarh district, Orissa, India that lies in the East Indian geothermal province. The study was performed to
delineate the fracture pattern, contaminated groundwater movement and possible heating source. VES interpretations suggest
a three- to four-layer structure in the area. Resistivity survey near the hot spring suggests that weathered and fractured
formations constitute the main aquifer system and extend to 60 m depth. Current flow measured at various electrode separations
normalized by the applied voltage suggests that fractures extend to a greater depth. Detailed VLF study shows that fractures
extend beyond 70 m depth. VLF anomaly has also very good correlation with the total magnetic field measured along the same
profiles. Study results suggest that a gridded pattern of VLF survey could map the underground conductive fracture zones that
can identify the movement of contaminated groundwater flow. Therefore, precautionary measures can be taken to check further
contamination by delineating subsurface conducting structures. Self potential (SP) measured over the hot spring does not show
a large anomaly in favor of the presence of a sulphide mineral body. A small positive (5–15mV) SP anomaly is measured which
may be streaming potential due to subsurface fluid flow. A high radiation is measured about four kilometers from the hot spring,
suggesting possible radiogenic heating. However, the exact nature of the heating source and its depth is not known in the
area. Deep resistivity followed by a magneto-telluric survey could reveal the deeper structures. 相似文献
11.
《Journal of Atmospheric and Solar》2008,70(15):1919-1928
This paper investigates the features of pre-earthquake ionospheric anomalies in the total electron content (TEC) data obtained on the basis of regular GPS observations from the International GNSS Service (IGS) network. For the analysis of the ionospheric effects of the 26 September 2005 Peru earthquake, Global Ionospheric Maps (GIMs) of TEC were used. The possible influence of the earthquake preparation processes on the main low-latitude ionosphere peculiarity—the equatorial anomaly—is discussed. Analysis of the TEC maps has shown that modification of the equatorial anomaly occurred a few days before the earthquake. In previous days, during the evening and night hours (local time—LT), a specific transformation of the TEC distribution had taken place. This modification took the shape of a double-crest structure with a trough near the epicenter, though usually in this time the restored normal latitudinal distribution with a maximum near the magnetic equator is observed. Additional measurements (CHAMP satellite) have also confirmed the presence of this structure. To compare the vertical TEC measurements obtained with GPS satellite signals (GPS TEC), the International Reference Ionosphere, IRI-2001, was used for calculating the IRI TEC. 相似文献
12.
K. T. KILTY 《Geophysical Prospecting》1984,32(1):51-62
The renewed interest in the self-potential method of exploration for mineral deposits gives an understanding of the self-potential mechanism new importance. The cause of SP anomalies in general lies in the interference between simultaneously occurring nonequilibrium phenomena. However, theories of the mechanism of mineral SP anomalies generally relate the SP anomaly to the equilibrium potential of the chemical reaction supposed to occur on the ore body surface. In this paper, I reformulate these equilibrium mechanisms in terms of nonequilibrium thermodynamics. The result is that the SP anomaly depends not on the equilibrium potential alone, but also on the potential resulting from current transferred across the ore body—electrolyte interface. It is not possible to calculate the overpotential theoretically because of the number of complicating factors, and experimental data are not available. This does not imply that SP data are uninterpretable quantitatively. SP data may be interpreted similarly to other potential field data. 相似文献
13.
The self-potential (S.P.) method, often employed in base-metal exploration, has successfully been applied to volcanological problems.Test surveys on the site of Mount Etna (Sicily) have revealed some positive anomalies as high as a few hundred millivolts over recent and old eruptive fissures. The S.P. technique allows one to determine the precise location of the fissures.The interpretation of the geophysical results (including S.P.), taking into account the structure of Mount Etna, has shown two important zones upon which several S.P. investigations have been carried out.Studies of the causes of these S.P. anomalies have shown the importance of the streaming potential as the principal source mechanism. 相似文献
14.
by A. Jardani A. Revil W. Barrash A. Crespy E. Rizzo S. Straface M. Cardiff B. Malama C. Miller and T. Johnson 《Ground water》2009,47(2):213-227
Ground water flow associated with pumping and injection tests generates self-potential signals that can be measured at the ground surface and used to estimate the pattern of ground water flow at depth. We propose an inversion of the self-potential signals that accounts for the heterogeneous nature of the aquifer and a relationship between the electrical resistivity and the streaming current coupling coefficient. We recast the inversion of the self-potential data into a Bayesian framework. Synthetic tests are performed showing the advantage in using self-potential signals in addition to in situ measurements of the potentiometric levels to reconstruct the shape of the water table. This methodology is applied to a new data set from a series of coordinated hydraulic tomography, self-potential, and electrical resistivity tomography experiments performed at the Boise Hydrogeophysical Research Site, Idaho. In particular, we examine one of the dipole hydraulic tests and its reciprocal to show the sensitivity of the self-potential signals to variations of the potentiometric levels under steady-state conditions. However, because of the high pumping rate, the response was also influenced by the Reynolds number , especially near the pumping well for a given test. Ground water flow in the inertial laminar flow regime is responsible for nonlinearity that is not yet accounted for in self-potential tomography. Numerical modeling addresses the sensitivity of the self-potential response to this problem. 相似文献
15.
Indrajit G. Roy 《Geophysical Prospecting》2020,68(3):1041-1056
We propose a strategy in designing an optimal set of filter parameters, such as the order of interpolating polynomial and the filter length for a Savitzky–Golay derivative filter. The proposed strategy is based on the ‘principle of parsimony’ while satisfying the optimality conditions. The optimality conditions are based on the Durbin–Watson lag-1 test statistic and the Derringer–Suich desirability function. While the former checks for an appropriate data fitting, the latter, on the other hand, ensures minimal shape distortion of the reconstructed response. The proposed strategy of designing filter parameters is developed and validated through numerical experiments using Gaussian pulse as a test function which is contaminated with additive white Gaussian noise. In the numerical tests, the polynomial orders used were 3, 5 and 7, but the filter length for each polynomial was varying until the optimality conditions were satisfied. The Savitzky–Golay derivative filtering is used in obtaining the robust reconstruction of noisy geophysical anomaly and the robust estimation of its first- and second-order derivatives. We validated the proposed technique on the published self-potential anomaly data using a data-based interpretation technique where the reconstructed anomaly and its first- and second-order derivatives were used in estimating model parameters. The data-based interpretation using the proposed technique of Savitzky–Golay derivative filtering provides a close agreement with the published results. 相似文献
16.
v--vUsing Frank and Wolfe's algorithm, a new interesting nonlinear programming technique has been developed in an attempt to estimate the geometric shape factor of a buried polarized body from a residual self-potential anomaly. Furthermore, the depth, the polarization angle and the electrical dipole moment have also been derived. This algorithm is noted to be robust and its application to SP data converges rapidly towards the optimal solution. The developed technique is tested through studying synthetic data with and without random noise. As a result, the near agreement between the model geometric shape factor and the evaluated one is well recognized. The validity of this proposed technique is tested on a field example from the Ergani Copper district, Turkey. The superiority of the nonlinear programming technique over other recently published methods is shown. 相似文献
17.
B. S. R. Rao I. V. Radhakrishna Murthy S. Jeevananda Reddy 《Pure and Applied Geophysics》1970,78(1):66-77
Summary An entirely new procedure for interpreting selfpotential anomalies of spheres, rods and dipping sheets is presented. The anomaly of a sphere is divided into two parts — the anomaly of odd symmetry and the anomaly of even symmetry — from which the depth can be obtained by fitting them with the master curves. The self-potential anomalies of a finite rod are transformed to the anomalies of a veritcal sheet, for which standard curves are presented. The case of a sheet was divided into three parts; (a) finite line of poles; (b) infinite double line of poles and (c) finite double line of poles. For the first case logarithmic curves were prepared and presented; by their comparison with the field profile, different parameters can be obtained. In the second case, a geometrical construction is provided to obtain the various values. In the third case, the anomalies of finite sheet (finite double line of poles) are transformed into those due to an infinite double line of poles for interpretation. 相似文献
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19.
A nomogram has been devised for situations, in which the source of a self-potential anomaly can be approximated by an obliquely polarized sphere or horizontal cylinder embedded in a homogeneous half space. The nomogram can be used for rapid determination of three parameters of the target: (1) depth to the centre, (2) angle between the axis of polarization and the horizontal, (3) shift of the point vertically above the centre of the body from zero potential value. The nomogram has been tested and the parameters determined for SP results obtained over ore bodies Weiss and Süleymanköy in the Ergani Copper district, Turkey. The curves computed for the estimated parameters match the field curves well. 相似文献
20.
为了研究五大连池火山区尾山火山锥浅层三维波速结构特征,在尾山火山锥附近区域布设了无线地震检波器密集台阵,记录连续地震背景噪声波形数据.基于微动方法(拓展空间自相关方法)提取了台站间2~5 Hz频率范围的Rayleigh面波相速度频散曲线.利用面波层析成像方法反演获得2~5 Hz Rayleigh面波二维相速度图像,基于每一个网格节点的频散曲线,进一步反演获得了尾山火山锥附近区域地表至700m深度的三维剪切波速度结构.成像结果显示:在0~150m较浅深度,靠近尾山火山锥区域显示为相对高速异常,远离火山锥区域则显示为相对低速异常.而至150~700m较深深度,波速异常特征与浅部相反,靠近尾山火山锥的区域显示为相对低速异常,远离火山锥的区域显示为相对高速异常.在远离尾山火山锥区域,浅层的相对低速异常可能与松散沉积层有关,深部的高速异常则反映了结晶变质岩的影响.在靠近尾山火山锥区域,浅部的相对高速异常应该反映了出露地表的玄武岩,而深部的相对低速异常则可能反映了火山通道周围广泛发育的破碎裂隙结构及其火山喷发后孔隙流体填充的影响. 相似文献