时间域航空电磁数据的反演   总被引：3，自引：0，他引：3  

黄皓平  王维中 《地球物理学报》1990,33(1):87-97

本文用广义逆矩阵理论讨论了时间域航空电磁数据的反演方法.以水平二层大地和球体模型为例进行了计算,结果表明这种方法对时间域电磁数据的反演是行之有效的.对于理论数据,一般仅需迭代数次即可稳定地收敛到真值.通过奇异值分析,可以确定一个模型中的相对重要参数和无关紧要参数;对于求解某一特定参数,可确定哪些数据起决定性的作用.由奇异值分解而得出的信息密度矩阵、模型分辨矩阵,分别给出了模型响应拟合数据和模型参数分辨率的度量.这些信息对于时间域航空电磁系统的设计、野外测量和资料解释都具有重要的参考价值.最后给出了实例.  相似文献   

Processes controlling 234U and 238U isotope fractionation and helium in the groundwater of the St. Lawrence Lowlands,Quebec: The potential role of natural rock fracturing     

《Applied Geochemistry》2016

The goal of this study is to explain the origin of ²³⁴U–²³⁸U fractionation in groundwater from sedimentary aquifers of the St. Lawrence Lowlands (Quebec, Canada), and its relationship with ³He/⁴He ratios, to gain insight regarding the evolution of groundwater in the region. (²³⁴U/²³⁸U) activity ratios, or (²³⁴U/²³⁸U)_act, were measured in 23 groundwater samples from shallow Quaternary unconsolidated sediments and from the deeper fractured regional aquifer of the Becancour River watershed. The lowest (²³⁴U/²³⁸U)_act, 1.14 ± 0.01, was measured in Ca–HCO₃-type freshwater from the Quaternary Shallower Aquifer, where bulk dissolution of the carbonate allows U to migrate into water with little ²³⁴U–²³⁸U isotopic fractionation. The (²³⁴U/²³⁸U)_act increases to 6.07 ± 0.14 in Na–HCO₃–Cl-type groundwater. Preferential migration of ²³⁴U into water by α-recoil is the underlying process responsible for this isotopic fractionation. An inverse relationship between (²³⁴U/²³⁸U)_act and ³He/⁴He ratios has been observed. This relationship reflects the mixing of newly recharged water, with (²³⁴U/²³⁸U)_act close to the secular equilibrium and containing atmospheric/tritiogenic helium, and mildly-mineralized older water (¹⁴C ages of 6.6 kyrs), with (²³⁴U/²³⁸U)_act of ≥6.07 and large amounts of radiogenic ⁴He, in excess of the steady-state amount produced in situ. The simultaneous fractionation of (²³⁴U/²³⁸U)_act and the addition of excess ⁴He could be locally controlled by stress-induced rock fracturing. This process increases the surface area of the aquifer matrix exposed to pore water, from which produced ⁴He and ²³⁴U can be released by α-recoil and diffusion. This process would also facilitate the release of radiogenic helium at rates greater than those supported by steady-state U–Th production in the rock. Consequently, sources internal to the aquifers could cause the radiogenic ⁴He excesses measured in groundwater.  相似文献   

Petrology of Medicine Lake Highland volcanics: Characterization of endmembers of magma mixing     

David C. Gerlach  Timothy L. Grove 《Contributions to Mineralogy and Petrology》1982,80(2):147-159

Lavas from Medicine Lake volcano, Northern California have been examined for evidence of magma mixing. Mixing of magmas has produced basaltic andesite, andesite, dacite and rhyolite lavas at the volcano. We are able to identify the compositional characteristics of the components that were mixed and to estimate the time lag between the mixing event and eruption of the mixed magma. Compositional data from pairs of phenocrysts identify a high alumina basalt (HAB) and a silicic rhyolite as endmembers of mixing. Mg-rich olivine or augite and Ca-rich plagioclase are associated with the HAB component, and Fe-rich orthopyroxene and Na-rich plagioclase are associated with the rhyolitic component. Some lavas contain multiple phenocryst assemblages suggesting the incorporation of several magmas intermediate between the HAB and silicic components. Glass inclusions trapped in Mg-rich olivine and Na-rich plagioclase are similar in composition to the proposed HAB and rhyolite end members and provide supportive evidence for mixing. Textural criteria are also consistent with magma mixing. Thermal curvature of the liquidus surfaces in the basalt-andesite-rhyolite system allows magmas produced by mixing to be either supercooled or superheated. Intergranular textures of basaltic andesites and andesites result from cooling initiated below the liquidus. The trachytic textures of silicic andesites form from cooling initiated above the liquidus. Reversed compositional zoning profiles in olivine crystals were produced by the mixing event, and the homogenization of the compositional zoning has been used to estimate the time interval between magma mixing and eruption. Time estimates are on the order of 80 to 90 h, suggesting that the mixing event triggered eruption.  相似文献   

Real-time seismic signal enhancement utilizing a hybrid Rao-Blackwellized particle filter and hidden Markov model filter   总被引：3，自引：0，他引：3  

Baziw  E. 《Geoscience and Remote Sensing Letters, IEEE》2005,2(4):418-422

This letter outlines a novel and robust algorithm for identifying seismic events within low signal-to-noise ratio (SNR) passive seismic data in real time. Since the event detection problem is a continuous, real-time process which has nonlinear mathematical representations, a Rao-Blackwellized particle filter (RBPF) is utilized. In this algorithm, a jump Markov linear Gaussian system (JMLGS) is defined where changes (i.e., jumps) in the state-space system and measurement equations are due to the occurrences and losses of events within the measurement noise. The RBPF obtains optimal estimates of the possible seismic events by individually weighting and subsequently summing a bank of Kalman filters (KFs). These KFs are specified and updated by samples drawn from a Markov chain distribution which defines the probability of the individual dynamical systems which compose the JMLGS. In addition, a hidden Markov model filter is utilized within the RBPF filter formulation so that real-time estimates of the phase of the seismic event can be obtained. The filter is demonstrated to provide up to an 80-fold improvement in the SNR when processing simulated seismic data with Gauss-Markov measurement noise.  相似文献   

Assessing Ar transport paths and mechanisms in the McClure Mountains hornblende     

I. M. Villa  B. Grobéty  S. P. Kelley  R. Trigila  R. Wieler 《Contributions to Mineralogy and Petrology》1996,126(1-2):67-80

 We have investigated the mechanisms and pathways by which Ar diffuses through the McClure Mountains hornblende (ferroan pargasite), selected as a good example of material normally dated during Ar-Ar studies. A coarse-grained hornblende separated from the same hand specimen as the MMhb-1 age standard was subjected to a hydrothermal cold-seal bomb experiment and characterized by TEM. Heated and unheated crystals were subjected to four different ³⁹Ar/⁴⁰Ar dating extraction techniques: conventional stepwise heating, infra-red laser spot, ultra-violet laser depth profiling, and closed-system stepwise etching. The stepwise heating age spectrum reproduces the features often interpreted as resulting from a concentric diffusive zonation, but the other three techniques yield results that are not compatible with such a simple picture. The IR laser data indicate that the dependence of laboratory Ar loss on grain size, predicted by Fickian diffusion, is at best poor and instead is related mainly to mineralogical variations. The depth profiles show the importance of planar zones (spaced between <1 and >150 μm from TEM evidence) in providing fast pathways for inward diffusion of atmospheric Ar from the capsule, but showed no evidence of diffusive profiles in the bulk of the hornblende lattice. The data from closed system stepwise etching underscore the role of zones rich in planar defects both for Ar loss and for nucleation of etching. The age spectra obtained by stepwise heating suffer from the differential breakdown of impurity phases, whose presence can be diagnosed with several isotope correlation plots; particularly revealing are Cl-Ca-K trends. In addition to the problems of mineral decomposition during in-vacuo laboratory degassing, an equally important decomposition occurs during many hydrothermal experiments which, combined with problems of mineral purity, have led to an overestimation of the rate of argon diffusion in hornblende. The response of hornblende to thermal disturbance in a hydrothermal environment can be every bit as complex as breakdown in vacuo. Laboratory experiments on bulk samples have not succeeded in quantitatively constraining volume diffusion. Received: 12 October 1995 / Accepted: 11 July 1996  相似文献   

Biot理论的唯象修正对S波特性的影响   总被引：5，自引：1，他引：5       下载免费PDF全文

席道瑛  易良坤  田象燕 《地球物理学报》2003,46(6):814-820

将复模量引入Biot方程后，在一维条件下通过S波的波动方程研究了S波的传播特性，S波的数值分析显示在频率域或温度域上都能获得热弛豫衰减峰和Biot衰减峰. 在频率域上由于温度的变化引起两峰相向位移,在温度域上,因频率的变化也发生相对移动. 随着温度和频率的不断提高，两峰发生叠加，叠加后两峰互换位置. 低频或低温段的热弛豫峰移到了高频或高温段，高频或高温段的Biot峰移到了低频或低温段.由于两峰的衰减机制不同，导致S波波速随频率或温度变化规律的复杂性. 这些规律已部分被共振实验所证实，证实该理论模型具有实验基础.  相似文献   

Measuring directional wave spectra using the 3D-ACM WAVE on fixedand taut-wire moorings     

McComb  P. Gorman  R. Black  K. Kun  A.L. 《Oceanic Engineering, IEEE Journal of》2001,26(2):171-180

Field data were analyzed from a simultaneous deployment of two 3D-ACM WAVE instruments; one on a fixed seabed frame in the nearshore zone, and the other further offshore on a taut-wire mooring. An intercomparison of measurements of vertical and horizontal wave-orbital currents with pressures was used to evaluate the velocity sensor response under field conditions. Results using the fixed frame have validated the measured horizontal wave-orbital velocities, but found the vertical velocities to be less coherent with the pressure time-series. The influence of the instrument mooring system on the velocity measurements was investigated. The oscillation of the taut-wire mooring was found to influence the magnitude of the measured horizontal wave-orbital velocities and induce a phase lag between velocity and sea-surface elevation. Examination of other data from similar taut-wire moorings indicates a systematic relationship between the length of the mooring cable and the measured phase lag, consistent with the behavior of the mooring system considered as a forced, linearly damped oscillator. A comparison was made between the spectra of wave direction derived from both velocity and pressure data with that derived solely from velocity data. The results show a high coherence for the fixed mooring, but significant directional variability in the higher frequencies (>0.13 Hz) on the taut-wire mooring we employed, which we attribute to the mooring oscillation. The analysis further indicates that on taut-wire moorings, the spectra of wave direction should be resolved solely from velocity data. Using these findings, directional wave spectra were produced for the nearshore and offshore sites from 233 coincident events over a two-month period, and these data are presented in a time-averaged spectral format  相似文献   

Provenance of Ordovician clastic sequences of the San Rafael Block (Central Argentina), with emphasis on the Ponón Trehué Formation     

P. Abre  C. Cingolani  U. Zimmermann  B. Cairncross  F. Chemale 《Gondwana Research》2011,19(1):275-290

The Ordovician Ponón Trehué Formation is the only early Palaeozoic sedimentary sequence known to record a primary contact with the Grenvillian-age basement of the Argentinean Cuyania terrane, in its southwards extension named the San Rafael block. Petrographic and geochemical data indicate contributions from a dominantly upper continental crustal component and a subordinated depleted component. Nd isotopes indicate ε_Nd of ? 4.6, ?_Sm/Nd ? 0.36 and T_DM 1.47 Ga in average. Pb-isotope ratios display average values for ²⁰⁶Pb/²⁰⁴Pb, ²⁰⁷Pb/²⁰⁴Pb, and ²⁰⁸Pb/²⁰⁴Pb of 19.15, 15.69 and 38.94 respectively. U–Pb detrital zircon ages from the Ponón Trehué Formation cluster around values of 1.2 Ga, indicating a main derivation from a local basement source (Cerro La Ventana Formation). The Upper Ordovician Pavón Formation records a younger episode of clastic sedimentation within the San Rafael block, and it shows a more complex detrital zircon age population (peaks at 1.1 and 1.4 Ga as well as Palaeoproterozoic and Neoproterozoic detrital grains). Detailed comparison between the two Ordovician clastic units indicates a shift with time in provenance from localized basement to more regional sources. Middle to early Upper Ordovician age is inferred for accretion of the Cuyania terrane to the proto-Andean margin of Gondwana.  相似文献   

Analysis of Decomposed Surface Currents in a Limited Area     

Yukiharu Hisaki 《Oceanic Engineering, IEEE Journal of》2006,31(4):768-778

A method of the Helmholtz decomposition for mapped surface currents on grid points is developed. This method is simple, and decomposed currents are not dependent on the distance from the open boundary. This decomposition is applied to surface currents observed by high-frequency (HF) radars. The observation was conducted from April to May 1998 east of Okinawa Island, Japan. The spectral analysis of decomposed currents reveals that the M₂ tidal peak for rotational components is much smaller than that for divergent components, which suggests that the barotropic tidal components are mainly included in divergent currents. The real-vector empirical orthogonal function (EOF) analysis of decomposed currents reveals an embedded eddy, which is related with the convergence of currents  相似文献   

Solution behavior of reduced COH volatiles in silicate melts at high pressure and temperature     

Bjorn O. Mysen  Marilyn L. Fogel  George D. Cody 《Geochimica et cosmochimica acta》2009,73(6):1696-6003

The solubility and solution mechanisms of reduced COH volatiles in Na₂OSiO₂ melts in equilibrium with a (H₂ + CH₄) fluid at the hydrogen fugacity defined by the iron-wüstite + H₂O buffer [f_H2(IW)] have been determined as a function of pressure (1-2.5 GPa) and silicate melt polymerization (NBO/Si: nonbridging oxygen per silicon) at 1400 °C. The solubility, calculated as CH₄, increases from ∼0.2 wt% to ∼0.5 wt% in the melt NBO/Si-range ∼0.4 to ∼1.0. The solubility is not significantly pressure-dependent, probably because f_H2(IW) in the 1-2.5 GPa range does not vary greatly with pressure. Carbon isotope fractionation between methane-saturated melts and (H₂ + CH₄) fluid varied by ∼14‰ in the NBO/Si-range of these melts.The (C..H) and (O..H) speciation in the quenched melts was determined with Raman and ¹H MAS NMR spectroscopy. The dominant (C..H)-bearing complexes are molecular methane, CH₄, and a complex or functional group that includes entities with CCH bonding. Minor abundance of complexes that include SiOCH₃ bonding is tentatively identified in some melts. There is no spectroscopic evidence for SiC or SiCH₃. Raman spectra indicate silicate melt depolymerization (increasing NBO/Si). The [CH₄/CCH]^melt abundance ratio is positively correlated with NBO/Si, which is interpreted to suggest that the (CCH)-containing structural entity is bonded to the silicate melt network structure via its nonbridging oxygen. The ∼14‰ carbon isotope fractionation change between fluid and melt is because of the speciation changes of carbon in the melt.  相似文献