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1.
The founder of the Russian school of direct interpretation of potential fields (with minimal prior geological‐geophysical information) was V.M. Berezkin, who introduced the operator of total normalized gradient for the 2D interpretation of profile gravity data sets. This operator was successfully applied in searches of hydrocarbon reservoirs. The further development of this approach (the so‐called quasi‐singular points method) has allowed solution also to various structural problems, using mathematical criteria for the transition from extremes of total normalized gradient fields to coordinates of anomalous sources. The main numerical evaluation strategy is based on stabilized downward continuation of field derivatives and specific use of the filtration properties of Fourier series approximation. The characteristic properties of the quasi‐singular points method are: 1) presentation of a more general total normalized gradient function through additional parameters (derivative order m, form of smoothing function Q, number of Fourier coefficients N* with maximal N), optimum values being chosen during a peak‐spectrum analysis of the interpreted function; 2) calculation of the set of total normalized gradient fields for various values of N*/N, representing coordinate systems {x,N*/N} as an ‘axes tree’ of extrema, where each 2D total normalized gradient field is representationally compressed in a 1D line, permitting a) immediate overview of the positions of the axes in all variants of the calculated fields and b) reduction of the retained information, as required in subsequent interpretation; 3) development of two criteria for transition from extrema of total normalized gradient fields to the coordinates of anomaly sources. The quasi‐singular points method is intended for tracing limiting gently‐sloping boundaries, if their micro‐relief features are sources of the interpreted anomaly but sub‐vertical contacts may also be traced. The method has been tested in delineating various geological structures. One of the most challenging, successfully achieved, was tracing of the Moho discontinuity and study of the upper mantle, using only Bouguer anomaly data along interpretation profiles. This is attested in an example of two regional profiles intersecting the European part of Russia. The central part of one of them coincides with the results from a deep seismic profile. 相似文献
2.
Stepanova I. E. Shchepetilov A. V. Mikhailov P. S. 《Izvestiya Physics of the Solid Earth》2022,58(3):406-419
Izvestiya, Physics of the Solid Earth - Abstract—The regional version of the method of linear integral representations is used to interpret the data on the anomalous physical fields of the... 相似文献
3.
陆地水储量是赋存在陆地上各种形式水的综合体现,研究其时空变化对认识区域水循环过程和水资源调控等具有重要意义。然而现有陆地水储量变化数据实际分辨率较低,限制了其在中小流域或地区中的应用。针对这一问题,本文基于GRACE重力卫星和其后续卫星GRACE-FO反演的陆地水储量变化数据,首先采用随机森林模型,分别基于格点、区域(流域)和区域(全国)3种空间降尺度思路将GRACE数据降尺度至0.25°×0.25°,后结合GLDAS模型数据,基于水量平衡原理计算得到地下水储量变化数据,最后基于降尺度模型模拟效果和实测地下水位数据评估3种降尺度思路在全国的适用性。结果表明:随机森林模型能够较好地模拟驱动数据(降水、气温、植被条件指数和土壤水储量)与GRACE数据的统计关系,验证期格点降尺度思路的平均相关系数总体在0.6左右,区域降尺度思路的平均纳什效率系数、相关系数和均方根误差分别>0.5、>0.75和<6.6 cm,3种空间降尺度思路的模拟精度均满足基本要求;2003—2021年间,GRACE数据、格点降尺度、区域降尺度(流域)和区域降尺度(全国)得到的我国陆地水储量亏缺量分别约为... 相似文献
4.
V. V. Spichak 《Surveys in Geophysics》1990,11(2-3):271-301
Two large groups of methods used to transform electromagnetic fields are discussed. The first of them includes methods based on the linear relations between the components of the MT-fields measured at a single or several points at the earth's surface. In this context special attention is paid to the consideration of impedance transformations, apparent resistivity and inductive operators, most frequently used in interpretation.The second group of methods concerns integral transformations of data. Firstly techniques are considered which are used for the division of the EM-fields into external and internal, normal and anomalous, surface and deep parts. Finally electromagnetic analogs of seismic methods are mentioned briefly.All transformations discussed are accompanied by examples of their use in data interpretation. 相似文献
5.
Yu. A. Kugaenko N. M. Kravchenko V. A. Saltykov 《Journal of Volcanology and Seismology》2009,3(3):168-178
We report extensive anomalies identified in seismicity parameters at different energy levels which were observed during the precursory process of the Karymskii seismovolcanic crisis of January 1–2, 1996. The seismicity of different energies includes earthquakes contained in the Kamchatka regional catalog and seismic noise (amplitudes of 10?9–10?12 m, frequencies of a few tens of hertz), which is a manifestation of the seismic process in the lowest energy range. The parameters of background seismicity are considered in retrospect using techniques for analyzing the dynamics of the seismic process: RTL and the Z function. Microseismicity is examined using these authors’ own method based on monitoring the response of high frequency seismic noise to tidal excitation 相似文献
6.
The airwave effect greatly influences the observational data from controlledsource electromagnetic exploration in shallow seas, which obscures the abnormal effects generated by exploration targets and, hence, affects the accuracy of the late exploration data interpretation. In this study, we propose a method to separate the main part from the anomalous field of marine controlled-source electromagnetic method (MCSEM) data based on Stratton–Chu integral transforms to eliminate the airwave effect, which dominates observed electromagnetic (EM) response in shallow seawater. This method of separating the main part from the anomalous field is a type of finite impulse response filter based on a discrete data set. Theoretical analysis proved that the method is stable and able to effectively depress noise. A numerical test indicated that the method could successfully eliminate the airwave effect from the observed EM signals generated by an air–water interface and a seawater layer. This technique is applicable for seawater models with either flat or rough seabeds. 相似文献
7.
Time domain electromagnetic (TDEM) response is usually associated with eddy currents in conductive bodies, since this is the dominant effect. However, other effects, such as displacement currents from dielectric processes and magnetic fields associated with rock magnetization, can contribute to TDEM response. In this paper we analyze the effect of magnetization on TDEM data. We use a 3-D code based on finite-difference method, developed by Wang and Hohmann [Geophysics 58 (1993) 797], to study transient electromagnetic field propagation through a medium containing bodies with both anomalous conductivity and anomalous magnetic permeability. The remarkable result is that the combination of anomalous conductivity and permeability within the same body could increase significantly the anomalous TDEM response in comparison with purely conductive or purely magnetic anomalies. This effect has to be taken into account in interpretation of TDEM data over electrical inhomogeneous structures with potentially anomalous magnetic permeability. 相似文献
8.
CHEN Po-fang 《地震学报(英文版)》2000,13(3):316-324
The geomagnetic night-time values were used to estimate the electromagnetic response function Q1 for half-year period. If the spatial structure of the source field can be described by the approximation, one can estimate the Q1 value using the single-station Z/H method. This technique enables us to carry out regional deep geomagnetic sounding by the method. The data used for analyses are geomagnetic night-time values for about, typically, 26 years from 5 good-quality stations and for several years from 34 stations distributed over the globe. The results indicate that the night-time values yield more reliable response estimates for half-year period compared to the usual estimates obtained from daily means. It implies that the approximation for the night-time fields holds good for the half-year period, but the daily means are not suitable for estimating the response function of the semi-annual variations by using the single-station method. Source field analyses for daily means data and night-time means data have also been carried out in this paper. 相似文献
9.
Based on spectral ratio method, a joint inversion method was used to obtain parameters of Lg wave attenuation and site response. The inversion method allows simple and direct (two-parameter) determination of Lg wave attenua- tion and site response from sparse spectral data, which are not affected by radiation pattern factor and different response of same instrument after geometrical spreading. The method was used successfully for estimating site re- sponse of stations of Zhejiang Seismic Network and measuring Lg wave attenuation. The study is based on 20 earth- quakes occurred in northeast of Taiwan with magnitude MS5.0~6.7 and 960 seismic wave records from 16 stations in Zhejiang area from 2002 to 2005. The parameters of site response and Lg attenuation were calculated with a fre- quency interval of 0.2 Hz in the range of 0.5 Hz to 10 Hz. Lg wave attenuation coefficient corresponding to U-D, E-W and N-S components are γ ( f )=0.00175 f 0.43485, γ ( f )=0.00145f 0.48467 and γ ( f )=0.0021f 0.41241, respectively. It is found that the site response is component-independent. It is also found that the site response of QIY station is significant above the frequency of 1.5 Hz, and that the site response of NIB station is low for most frequency 相似文献
10.
George R. Jiracek 《Surveys in Geophysics》1990,11(2-3):163-203
11.
A method is presented for determining bounds of the properties of axial symmetric bodies from a finite number of gravity and magnetic observations based on Parker's theory of ideal bodies. Bounds on the density contrast and the intensity of magnetization are calculated as a function of depth to the top of the anomalous source, restricting the range of smallest possible solutions to fit the data. The model studied is approximated by an array of vertical annuli cylinders, each of uniform density and magnetization. Linear programming algorithms based on the ideal body theory were used to calculate the distribution of these parameters within the body. Simultaneous inversion of gravity and magnetic data is performed assuming a constant ratio between the density contrast and the intensity of magnetization and that a common body is responsible for both observed fields. The parameter k(|J|/δp) provides information about the rock type of the structure. Interpretation of gravity and aeromagnetic data from Darnley Bay, NWT, Canada, indicated the presence of a shallow ultrabasic intrusion. 相似文献
12.
J. Torquil Smith H. Frank Morrison Lawrence R. Doolittle Hung-Wen Tseng 《Journal of Applied Geophysics》2007,61(3-4):227-234
Equivalent dipole polarizabilities are a succinct way to summarize the inductive response of an isolated conductive body at distances greater than the scale of the body. Their estimation requires measurement of secondary magnetic fields due to currents induced in the body by time varying magnetic fields in at least three linearly independent (e.g., orthogonal) directions. Secondary fields due to an object are typically orders of magnitude smaller than the primary inducing fields near the primary field sources (transmitters). Receiver coils may be oriented orthogonal to primary fields from one or two transmitters, nulling their response to those fields, but simultaneously nulling to fields of additional transmitters is problematic. If transmitter coils are constructed symmetrically with respect to inversion in a point, their magnetic fields are symmetric with respect to that point. If receiver coils are operated in pairs symmetric with respect to inversion in the same point, then their differenced output is insensitive to the primary fields of any symmetrically constructed transmitters, allowing nulling to three (or more) transmitters. With a sufficient number of receivers pairs, object equivalent dipole polarizabilities can be estimated in situ from measurements at a single instrument sitting, eliminating effects of inaccurate instrument location on polarizability estimates. The method is illustrated with data from a multi-transmitter multi-receiver system with primary field nulling through differenced receiver pairs, interpreted in terms of principal equivalent dipole polarizabilities as a function of time. 相似文献
13.
用地磁夜均值资料研究半年周期变化的电磁响应 (地磁内外场比值 Q1) ,如夜均值半年周期变化的源场分布符合 P01分布模式 ,则可用单台资料进行计算 ,有利于进行地区性深地磁测深的研究 .本文选择了质量较好的 5个台约 2 6年的连续资料 ,又搜集了可用的全球分布的台站资料进行分析计算 .结果表明 ,从夜均值估算的半年周期变化的 Q1更为可靠 .原因可能是源场模式不同 .一般的日均值资料不符合 P01模式 ,而夜均值资料则比较符合 P01模式 .本文对此作了源场分布的研究 . 相似文献
14.
GUO HUA FAN TONG QI YAO KE LI HAN KE JIA ZHU ZUO WEN GU Institute of Geophysics China Seismological Bureau Beijing China 《地震学报(英文版)》1998,11(6):719-727
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15.
—?We present a hybrid boundary-element (BE) and generalized screen propagator (GSP) method for the 2-D SH problem to model the combined effects of arbitrarily irregular topography, large-scale crustal variation, and the associated small-scale heterogeneities on regional wave propagation. We develop a boundary connection technique to couple the wave fields calculated by the BE method with those of the GSP method. Its validity is tested by numerical experiments. For a long crustal waveguide, the relatively short sections with severe surface topography can be modeled by the time-consuming BE method to high frequencies, and the exterior field in the relatively weak heterogeneous media of large volume can be calculated by the GSP method. For the waveguide with severe topography, the BE method can be used section by section via the boundary connection technique to model the combined effects of rough topography and large-scale structural variation on Lg wave propagation at extended regional distances.¶Numerical comparisons with independent methods showed that the hybrid method is relatively accurate for Lg simulation. We apply the hybrid method to Lg wave propagation in two real crustal waveguides in the Tibet region; one with Lg blockage and another without blockage. We found that the most characteristic effect from the irregular topography is the strong scattering by the topographic structures. The scattering by local irregular topographies leads to anomalous near-receive effects and tends to remove energy from the guided waves, which causes decay of amplitude and waveform distortion. It can be expected that rough surface topography and random heterogeneities with scale length close to the dominant wavelength will be very efficient in attenuating regional waves. The dramatic lateral variation of the topography-Moho large-scale structure combined with the small-scale rough topography and random heterogeneities could be the cause of Lg anomalous attenuation and blockage observed in this region. More quantitative assessment of the topographic effects must be conducted in the future. 相似文献
16.
The computerized ionospheric tomography is a method for imaging the Earth’s ionosphere using a sounding technique and computing the slant total electron content (STEC) values from data of the global positioning system (GPS). The most common approach for ionospheric tomography is the voxel-based model, in which (1) the ionosphere is divided into voxels, (2) the STEC is then measured along (many) satellite signal paths, and finally (3) an inversion procedure is applied to reconstruct the electron density distribution of the ionosphere. In this study, a computationally efficient approach is introduced, which improves the inversion procedure of step 3. Our proposed method combines the empirical orthogonal function and the spherical Slepian base functions to describe the vertical and horizontal distribution of electron density, respectively. Thus, it can be applied on regional and global case studies. Numerical application is demonstrated using the ground-based GPS data over South America. Our results are validated against ionospheric tomography obtained from the constellation observing system for meteorology, ionosphere, and climate (COSMIC) observations and the global ionosphere map estimated by international centers, as well as by comparison with STEC derived from independent GPS stations. Using the proposed approach, we find that while using 30 GPS measurements in South America, one can achieve comparable accuracy with those from COSMIC data within the reported accuracy (1 × 1011 el/cm3) of the product. Comparisons with real observations of two GPS stations indicate an absolute difference is less than 2 TECU (where 1 total electron content unit, TECU, is 1016 electrons/m2). 相似文献
17.
Dongmei Han Xing Liang Matthew J. Currell Xianfang Song Zongyu Chen Menggui Jin Changming Liu Ying Han 《水文研究》2010,24(22):3157-3176
The conceptual hydrogeological model of the low to medium temperature Daying and Qicun geothermal fields has been proposed, based on hydrochemical characteristics and isotopic compositions. The two geothermal fields are located in the Xinzhou basin of Shanxi, China and exhibit similarities in their broad‐scale flow patterns. Geothermal water is derived from the regional groundwater flow system of the basin and is characterized by Cl·SO4‐Na type. Thermal water is hydrochemically distinct from cold groundwater having higher total dissolved solids (TDS) (>0·8 g/l) and Sr contents, but relatively low Ca, Mg and HCO3 contents. Most shallow groundwater belongs to local flow systems which are subject to evaporation and mixing with irrigation returns. The groundwater residence times estimated by tritium and 14C activities indicate that deep non‐thermal groundwater (130–160 m) in the Daying region range from modern (post‐1950s) in the piedmont area to more than 9·4 ka BP (Before Present) in the downriver area and imply that this water belong to an intermediate flow system. Thermal water in the two geothermal fields contains no detectable active 14C, indicating long residence times (>50 ka), consistent with this water being part of a large regional flow system. The mean recharge elevation estimated by using the obtained relationship Altitude (m) = ? 23·8 × δ2H (‰ ) ? 121·3, is 1980 and 1880 m for the Daying and Qicun geothermal fields, respectively. The annual infiltration rates in the Daying and Qicun geothermal fields can be estimated to be 9029 × 103 and 4107 × 103 m3/a, respectively. The variable 86Sr/87Sr values in the thermal and non‐thermal groundwater in the two fields reflect different lithologies encountered along the flow path(s) and possibly different extents of water‐rock interaction. Based on the analysis of groundwater flow systems in the two geothermal fields, hydrogeochemical inverse modelling was performed to indicate the possible water‐rock interaction processes that occur under different scenarios. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
18.
A procedure is proposed for geochemical mapping of the water area bottom based on the subdivision of raw data into two components, i.e., systematic (regional) and random (local). The former is used to determine regional characteristic of the spatial radionuclide distributions in bottom sediments to be utilized to identify large radiogeochemical regions, while the latter is used to identify local anomalies and evaluate their characteristics. The systematic component of the radiogeochemical field is determined by trend analysis. Next, cluster analysis, i.e., hierarchic clusterization of the results of trend analysis followed by associative classification, is used for radiochemical zoning of the water area. After that, maps are constructed, showing contour lines of the local component of radiogeochemical fields, represented by deviations of the value in the given point from the trend. The result is a single map showing the radiogeochemical regions with contour lines of normalized anomalous activities of the radionuclides under study. The practical application of the method is illustrated by radiogeochemical mapping of the bed in the Eastern Gulf of Finland. 相似文献
19.
The 2010 boreal summer marked a worldwide abnormal climate. An unprecedented heat wave struck East Asia in July and August 2010. In addition to this, the tropical Indian Ocean was abnormally warm during the summer of 2010. Several heavy rainfall events and associated floods were also reported in the Indian monsoon region. During the season, the monsoon trough (an east–west elongated area of low pressure) was mostly located south of its normal position and monsoon low pressure systems moved south of their normal tracks. This resulted in an uneven spatial distribution with above-normal rainfall over peninsular and Northwest India, and deficient rainfall over central and northeastern parts of India, thus prediction (and simulation) of such anomalous climatic summer season is important. In this context, evolution of vertical moist thermodynamic structure associated with Indian summer monsoon 2010 is studied using regional climate model, reanalysis and satellite observations. This synergised approach is the first of its kind to the best of our knowledge. The model-simulated fields (pressure, temperature, winds and precipitation) are comparable with the respective in situ and reanalysis fields, both in intensity and geographical distribution. The correlation coefficient between model and observed precipitation is 0.5 and the root-mean-square error (RMSE) is 4.8 mm day?1. Inter-comparison of model-simulated fields with satellite observations reveals that the midtropospheric temperature [Water vapour mixing ratio (WVMR)] has RMSE of 0.5 K (1.6 g kg?1), whereas the surface temperature (WVMR) has RMSE of 3.4 K (2.2 g kg?1). Similarly, temporal evolution of vertical structure of temperature with rainfall over central Indian region reveals that the baroclinic nature of monsoon is simulated by the model. The midtropospheric warming associated with rainfall is captured by the model, whereas the model failed to capture the surface response to high and low rainfall events. The model has strong water vapour loading in the whole troposphere, but weaker coherent response with rainfall compared to observations. Thus, strong water vapour loading and overestimation of rainfall are reported in the model. This study put forward that the discrepancy in the model-simulated structure may be reduced by assimilation of satellite observations. 相似文献
20.
Greg Balco Jason Briner Robert C. Finkel John A. Rayburn John C. Ridge Joerg M. Schaefer 《Quaternary Geochronology》2009,4(2):93-107
The major uncertainty in relating cosmogenic-nuclide exposure ages to ages measured by other dating methods comes from extrapolating nuclide production rates measured at globally scattered calibration sites to the sites of unknown age that are to be dated. This uncertainty can be reduced by locating production rate calibration sites that are similar in location and age to the sites to be dated. We use this strategy to reconcile exposure age and radiocarbon deglaciation chronologies for northeastern North America by compiling 10Be production rate calibration measurements from independently dated late-glacial and early Holocene ice-marginal landforms in this region. 10Be production rates measured at these sites are 6–12% lower than predicted by the commonly accepted global 10Be calibration data set used with any published production rate scaling scheme. In addition, the regional calibration data set shows significantly less internal scatter than the global calibration data set. Thus, this calibration data set can be used to improve both the precision and accuracy of exposure dating of regional late-glacial events. For example, if the global calibration data set is used to calculate exposure ages, the exposure-age deglaciation chronology for central New England is inconsistent with the deglaciation chronology inferred from radiocarbon dating and varve stratigraphy. We show that using the regional data set instead makes the exposure age and radiocarbon chronologies consistent. This increases confidence in correlating exposure ages of ice-marginal landforms in northeastern North America with glacial and climate events dated by other means. 相似文献