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Sample records for magnetotelluric method mmt

  1. Magnetotellurics as a multiscale geophysical exploration method

    NASA Astrophysics Data System (ADS)

    Carbonari, Rolando; D'Auria, Luca; Di Maio, Rosa; Petrillo, Zaccaria

    2016-04-01

    Magnetotellurics (MT) is a geophysical method based on the use of natural electromagnetic signals to define subsurface electrical resistivity structure through electromagnetic induction. MT waves are generated in the Earth's atmosphere and magnetosphere by a range of physical processes, such as magnetic storms, micropulsations, lightning activity. Since the underground MT wave propagation is of diffusive type, the longer is the wavelength (i.e. the lower the wave frequency) the deeper will be the propagation depth. Considering the frequency band commonly used in MT prospecting (10-4 Hz to 104 Hz), the investigation depth ranges from few hundred meters to hundreds of kilometers. This means that magnetotellurics is inherently a multiscale method and, thus, appropriate for applications at different scale ranging from aquifer system characterization to petroleum and geothermal research. In this perspective, the application of the Wavelet transform to the MT data analysis could represent an excellent tool to emphasize characteristics of the MT signal at different scales. In this note, the potentiality of such an approach is studied. In particular, we show that the use of a Discrete Wavelet (DW) decomposition of measured MT time-series data allows to retrieve robust information about the subsoil resistivity over a wide range of spatial (depth) scales, spanning up to 5 orders of magnitude. Furthermore, the application of DWs to MT data analysis has proven to be a flexible tool for advanced data processing (e.g. non-linear filtering, denoising and clustering).

  2. Quadratic function approaching method for magnetotelluric soundingdata inversion

    SciTech Connect

    Liangjun, Yan; Wenbao, Hu; Zhang, Keni

    2004-04-05

    The quadratic function approaching method (QFAM) is introduced for magnetotelluric sounding (MT) data inversion. The method takes the advantage of that quadratic function has single extreme value, which avoids leading to an inversion solution for local minimum and ensures the solution for global minimization of an objective function. The method does not need calculation of sensitivity matrix and not require a strict initial earth model. Examples for synthetic data and field measurement data indicate that the proposed inversion method is effective.

  3. A new method to compensate for bias in magnetotellurics

    NASA Astrophysics Data System (ADS)

    Müller, A.

    2000-07-01

    Error estimates from statistical regression analysis are often obviously too small, leading to doubts about the given equations, the statistical method itself and finally, with resignation, to the conclusion that mathematical equations and reality never agree. However, for magnetotelluric data we have found an almost perfect fit between observed scattering and predicted confidence limits of regression coefficients after accounting for a systematic error-the bias. Different methods to compensate for bias in magnetotelluric impedance estimation have been described using additional data from a reference station. However, sufficiently accurate reference data are often not available. A new method has been developed that enables bias compensation without additional data. For the new method we derive a linear relationship between the effect of bias and an expression depending on the data fit. From this we extrapolate the solution for the unbiased impedance. The new method assumes a special model of uncorrelated noise as well as an approximation for the structure of the impedance tensor. From each pair of components of the unrotated impedance tensor corresponding to the same output channel, one of the pair can be compensated if its magnitude is large compared to that of the other. The method has been successfully applied in many cases. We claim that the solution is closer to the true impedance than any solution based on the selection of events. It gives a measure of the partitioning of noise between the electric and magnetic channels. We applied the method to measurements from the North Anatolian Fault Zone (Turkey) and from the Merapi volcano (Central Java) in the period range 10-2500s. Different instrumentation was used for the two sets of measurements, but in both cases we used fluxgate magnetometers to measure the magnetic variations.

  4. On resolution of the method of directional magnetotelluric soundings

    NASA Astrophysics Data System (ADS)

    Savin, Mihail

    2015-12-01

    The problem is to examine the resolution of directional magnetotelluric soundings (DMTS). Abrupt changes of impedances Z^e,h of electrical and magnetic types in critical region of parameters R 0, Jωμσ where R=Re[(K_x)2+(K_y)2], J=Im[(K_x)2+(K_y)2] are shown to result in significantly higher resolution of the method as compared with the traditional interpretation using Tikhonov-Cagniard impedance Z^0. The stability of solution of DMTS method inverse problem is considered subject to field measurement errors limited the resolution. The minimum of the limits is determined for the conductivity Δσ/σ small variations. For studying DMTS resolution as applied to MT monitoring of earthquake site the mathematical experiment for three-layer geoelectric model was carried out. When changing the earthquake site conductivity of Δσ ∼ ±10 variations of reflection coefficient of electric mode ΔQe are in the range of 20% that is significantly more than the field measurement error. The possibility for prediction modeling in the context of obtained results is discussed.

  5. A new magnetotelluric inversion scheme using generalized RRI method

    NASA Astrophysics Data System (ADS)

    Yamane, Kazunobu; Takasugi, Shinji; Lee, Ki Ha

    1996-09-01

    A new two-dimensional (2-D) magnetotelluric (MT) inversion scheme is proposed in this paper. This scheme is based on a locally 2-D analysis in order to minimize computational time and computer memory. The MT governing equation is linearized in terms of the magnetic field and electrical conductivity for the perturbation analysis. The perturbed equation is then multiplied by a test function and integrated over the cross-section. Integrating by parts and then substituting this test function with local magnetic fields, a new equation is obtained that is a 2-D variational integral for the electrical conductivity. The new equation is general in the sense that it can explicitly include the horizontal derivative of the magnetic field. If the horizontal derivative term is eliminated, the new equation becomes identical to the Rapid Relaxation Inversion (RRI) scheme proposed by Smith and Booker (J. Geophys. Res., 96: 3905-3922, 1991).

  6. Numerical solution of 3-D magnetotelluric using vector finite element method

    NASA Astrophysics Data System (ADS)

    Prihantoro, Rudy; Sutarno, Doddy; Nurhasan

    2015-09-01

    Magnetotelluric (MT) is a passive electromagnetic (EM) method which measure natural variations of electric and magnetic vector fields at the Earth surface to map subsurface electrical conductivity/resistivity structure. In this study, we obtained numerical solution of three-dimensional (3-D) MT using vector finite element method by solving second order Maxwell differential equation describing diffusion of plane wave through the conductive earth. Rather than the nodes of the element, the edges of the element is used as a vector basis to overcome the occurrence of nonphysical solutions that usually faced by scalar (node based) finite element method. Electric vector fields formulation was used and the resulting system of equation was solved using direct solution method to obtain the electric vector field distribution throughout the earth resistivity model structure. The resulting MT response functions was verified with 1-D layered Earth and 3-D2 COMMEMI outcropping structure. Good agreement is achieved for both structure models.

  7. Efficient computational methods for electromagnetic imaging with applications to 3D magnetotellurics

    NASA Astrophysics Data System (ADS)

    Kordy, Michal Adam

    The motivation for this work is the forward and inverse problem for magnetotellurics, a frequency domain electromagnetic remote-sensing geophysical method used in mineral, geothermal, and groundwater exploration. The dissertation consists of four papers. In the first paper, we prove the existence and uniqueness of a representation of any vector field in H(curl) by a vector lying in H(curl) and H(div). It allows us to represent electric or magnetic fields by another vector field, for which nodal finite element approximation may be used in the case of non-constant electromagnetic properties. With this approach, the system matrix does not become ill-posed for low-frequency. In the second paper, we consider hexahedral finite element approximation of an electric field for the magnetotelluric forward problem. The near-null space of the system matrix for low frequencies makes the numerical solution unstable in the air. We show that the proper solution may obtained by applying a correction on the null space of the curl. It is done by solving a Poisson equation using discrete Helmholtz decomposition. We parallelize the forward code on multicore workstation with large RAM. In the next paper, we use the forward code in the inversion. Regularization of the inversion is done by using the second norm of the logarithm of conductivity. The data space Gauss-Newton approach allows for significant savings in memory and computational time. We show the efficiency of the method by considering a number of synthetic inversions and we apply it to real data collected in Cascade Mountains. The last paper considers a cross-frequency interpolation of the forward response as well as the Jacobian. We consider Pade approximation through model order reduction and rational Krylov subspace. The interpolating frequencies are chosen adaptively in order to minimize the maximum error of interpolation. Two error indicator functions are compared. We prove a theorem of almost always lucky failure in the

  8. Polarisation analysis of magnetotelluric time series using a wavelet-based scheme: A method for detection and characterisation of cultural noise sources

    NASA Astrophysics Data System (ADS)

    Escalas, M.; Queralt, P.; Ledo, J.; Marcuello, A.

    2013-05-01

    The identification and elimination of cultural noise that affects magnetotelluric (MT) time series presents a challenge in the vicinity of industrialised, urban or farming areas. Most noise sources are fixed in space and create a signal with certain polarisation properties. In this paper, we propose a new method for detection and characterisation of cultural noise sources in magnetotelluric time series based on polarisation analysis of the electromagnetic signal in the time-frequency domain using a wavelet scheme. We tested the proposed method with synthetic polarised signals and experimental time series corresponding to a field experiment with a controlled EM source and several MT real cases. The results demonstrated the difference between the polarisation properties of the natural MT signal and the signal contaminated by a controlled source or by cultural noise.

  9. Quasibreathers in the MMT model

    NASA Astrophysics Data System (ADS)

    Pushkarev, A.; Zakharov, V. E.

    2013-04-01

    We report numerical detection of a new type of localized structures in the frame of Majda-McLaughlin-Tabak (MMT) model adjusted for description of essentially nonlinear gravity waves on the surface of ideal deep water. These structures-quasibreathers or oscillating quasisolitons-can be treated as groups of freak waves closely resembling experimentally observed “Three Sisters” wave packets on the ocean surface. The MMT model has quasisolitonic solutions. Unlike NLSE solitons, MMT quasisolitons are permanently backward radiating energy, but nevertheless do exist during thousands of carrier wave periods. Quasisolitons of small amplitude are regular and stable, but large-amplitude ones demonstrate oscillations of amplitude and spectral shape. This effect can be explained by periodic formation of weak collapses, carrying out negligibly small amount of energy. We call oscillating quasisolitons “quasibreathers”.

  10. Method for Simultaneously improving the thermal stability and mechanical properties of poly(lactic acid): effect of high-energy electrons on the morphological, mechanical, and thermal properties of PLA/MMT nanocomposites.

    PubMed

    Wang, De-Yi; Gohs, Uwe; Kang, Nian-Jun; Leuteritz, Andreas; Boldt, Regine; Wagenknecht, Udo; Heinrich, Gert

    2012-08-28

    Nanocomposites derived from poly(lactic acid) (PLA) and organically modified montmorillonite (oMMT) have been cross-linked by high-energy electrons in the presence of triallyl cyanurate (TAC). The morphology of untreated and cross-linked PLA/MMT nanocomposites was characterized by wide-angle X-ray scattering (WAXS) and transmission electron microscopy (TEM). This treatment can improve both the thermal stability and the glass-transition temperatures of the PLA nanocomposites (e.g., PLA-MMT-TAC 30kGy, 50kGy, and 70kGy) because of the formation of cross-linking structures in the nanocomposites that will considerably reduce the mobility of polymers. Interestingly, at relatively low irradiation doses (e.g., 30 and 50 kGy) a good balance between tensile strength and elongation at break for the PLA nanocomposites could be achieved. These mechanical properties are superior to those of pure PLA. Therefore, combining nanotechnology and electron beam cross-linking is a promising new method of simultaneously improving the mechanical properties (toughness and tensile strength) and thermal stability of PLA. PMID:22845883

  11. The subsurface cross section resistivity using magnetotelluric method in Pelabuhan Ratu area, West Java, implication for geological hazard mitigation

    NASA Astrophysics Data System (ADS)

    Gaffar, Eddy Z.

    2016-02-01

    Pelabuhan Ratu area is located on the south coast of West Java. Pelabuhan Ratu area's rapid development and population growth were partly stimulated by the Indonesian Government Regulation No. 66 the year 1998 that made Pelabuhan Ratu the capital city of the district of Sukabumi. Because of this fact, it is very important to create a geological hazard mitigation plan for the area. Pelabuhan Ratu were passed by two major faults: Cimandiri fault in the western and Citarik fault in the eastern. Cimandiri fault starts from the upstream of Cimandiri River to the southern of Sukabumi and Cianjur city. While Citarik fault starts from the Citarik River until the Salak Mountain. These two faults needs to be observed closely as they are prone to cause earthquake in the area. To mitigate earthquake that is estimated will occur at Cimandiri fault or the Citarik fault, the Research Center for Geotechnology LIPI conducted research using Magnetotelluric (MT) method with artificial Phoenix MT tool to determine the cross-section resistivity of the Pelabuhan Ratu and the surrounding area. Measurements were taken at 40 points along the highway towards Jampang to Pelabuhan Ratu, and to Bandung towards Cibadak with a distance of less than 500 meters between the measuring points. Measurement results using this tool will generate AMT cross-section resistivity to a depth of 1500 meters below the surface. Cross-section resistivity measurement results showed that there was a layer of rock with about 10 Ohm-m to 1000 Ohm-m resistivity. Rocks with resistivity of 10 Ohm-m was interpreted as conductive rocks that were loose or sandstone containing water. If an earthquake to occur in this area, it will lead to a strong movement and liquefaction that will destroy buildings and potentially cause casualties in this area.

  12. A Study of Static Shift Removal Methods in a 3D Magnetotelluric Survey at Pisagua Fault, Chile.

    NASA Astrophysics Data System (ADS)

    Bascur, J.; Comte, D.; Dias, D.; Siripunvaraporn, W.

    2014-12-01

    The static shift is one of the main problems that cause misleads in the magnetotellurics (MT) interpretation. This work presents a study comparing methods for removing the static shift effect from MT data acquired around the Pisagua Fault in Chile (2014). This evaluation considers the methods based on the joint inversion of the subsurface resistivity with the static shift effect and the calibration based on the TDEM data.First, it was developed a formulation in the data space, following the work of W. Siripunvaraporn (2005), that allows the joint inversion of the resistivity model and the static shift effect. That formulation makes it possible to use any linear representation for removing the static shift in the MT stations. This property permits compare the representation proposed by Sasaki (2004) and the static shift tensor, which use a 2x2 matrix to correct the effect. The last one is suggested to be a better model for 3D MT responses, because it can reproduce the distortion on the phase of MT data.Twenty one stations, measuring MT and TDEM methods, were acquired at the east side of the Pisagua town in the North of Chile (figure). In this place, there is an evident scarp on the topography that reveals the existence of an important fault (Pisagua Fault). Also, the Chilean desert at this location is characterized by the presence of shallow nitrate deposits (called "caliche"), whose have an elevated electrical resistance and can produce the static shift effect in the MT stations. For those reasons it was expected that the sector around the Pisagua Fault was an adequate place to evaluate static correction methods, because the data certainly would be distorted by the static shift and a successful correction method should reveal the fault observed at surface.The MT data acquired have mostly a 3D dimensionality (using A. Marti criteria, 2009) and show signs of being static shifted. A 3D inversion of this data, without considering the static shift, results in a poor

  13. MMT and Magellan infrared spectrograph

    NASA Astrophysics Data System (ADS)

    McLeod, Brian A.; Fabricant, Daniel; Geary, John; Martini, Paul; Nystrom, George; Elston, Richard; Eikenberry, Stephen S.; Epps, Harland

    2004-09-01

    We present the preliminary design for the MMT and Magellan Infrared Spectrograph (MMIRS). MMIRS is a fully refractive imager and multi-object spectrograph that uses a 2048x2048 pixel Hawaii2 HgCdTe array. It offers a 7'x7' imaging field of view and a 4'x7' field of view for multi-object spectroscopy. Dispersion is provided by a set of 5 grisms providing R=3000 at J, H, or K, or R=1300 in J+H or H+K.

  14. Parallel three-dimensional magnetotelluric inversion using adaptive finite-element method. Part I: theory and synthetic study

    NASA Astrophysics Data System (ADS)

    Grayver, Alexander V.

    2015-07-01

    This paper presents a distributed magnetotelluric inversion scheme based on adaptive finite-element method (FEM). The key novel aspect of the introduced algorithm is the use of automatic mesh refinement techniques for both forward and inverse modelling. These techniques alleviate tedious and subjective procedure of choosing a suitable model parametrization. To avoid overparametrization, meshes for forward and inverse problems were decoupled. For calculation of accurate electromagnetic (EM) responses, automatic mesh refinement algorithm based on a goal-oriented error estimator has been adopted. For further efficiency gain, EM fields for each frequency were calculated using independent meshes in order to account for substantially different spatial behaviour of the fields over a wide range of frequencies. An automatic approach for efficient initial mesh design in inverse problems based on linearized model resolution matrix was developed. To make this algorithm suitable for large-scale problems, it was proposed to use a low-rank approximation of the linearized model resolution matrix. In order to fill a gap between initial and true model complexities and resolve emerging 3-D structures better, an algorithm for adaptive inverse mesh refinement was derived. Within this algorithm, spatial variations of the imaged parameter are calculated and mesh is refined in the neighborhoods of points with the largest variations. A series of numerical tests were performed to demonstrate the utility of the presented algorithms. Adaptive mesh refinement based on the model resolution estimates provides an efficient tool to derive initial meshes which account for arbitrary survey layouts, data types, frequency content and measurement uncertainties. Furthermore, the algorithm is capable to deliver meshes suitable to resolve features on multiple scales while keeping number of unknowns low. However, such meshes exhibit dependency on an initial model guess. Additionally, it is demonstrated

  15. Hydrogeological investigation in Santiago Island (Cabo Verde) using magnetotellurics and VLF methods

    NASA Astrophysics Data System (ADS)

    Monteiro Santos, Fernando A.; Almeida, Eugénio P.; Gomes, Mota; Pina, António

    2006-08-01

    A geoelectromagnetic research was carried out in the Santa Cruz region (Santiago Island, Cabo Verde) during June 2004. The survey comprised MT soundings and VLF profiles. The main purpose of the MT profile, carried out across three important valleys associated with freshwater aquifers, was to study the tectonic structures correlated to seawater infiltration. The VLF method was used inside of the valleys for investigating shallow structures related to the aquifer contamination by seawater. Numerical modelling shows that the ocean effect is not important for MT data collected at periods shorter than 1 s. The MT data were inverted using a two-dimensional approach, to obtain the sub-superficial electrical conductivity distribution. The VLF data were processed applying the Karous-Hjelt filters to obtain the equivalent current distribution and inverted using 2-D approach. The results obtained in one of the most important valleys show anomalous current concentration/low resistivity (<20 Ω m) areas at depths greater than 40 m that may correspond to an increase in seawater content. The MT data modelling show that the deep zones beneath the valley are strongly fractured representing good pathways for seawater circulation. The depth of the conductive zones increases from south to north, suggesting a northward decreasing of the seawater infiltration effect. This observation correlates very well with in situ geochemical observations.

  16. MMT adaptive secondary prototype development

    NASA Astrophysics Data System (ADS)

    Biasi, Roberto; Gallieni, Daniele

    1998-09-01

    We designed and manufacture dan 'Adaptive Secondary Mirror 30 Actuators Prototype' that represents as much as possible the final MMT adaptive optics unit for what concerns mechanical, electronic and cooling system issues. Moreover, different actuator designs have been tested by using the same test bench. The adaptive secondary is based on a thin continuous facesheet mirror moved by electromagnetic actuators. Permanent magnets are glued on the mirror, while voice coils are connected to the support structure by cold fingers. A capacitive sensor co-located with each actuator measures the local gap between the mirror and a reference back plate. Voice coil motors allow to perform chopping and tip-tilt correction by using directly the deformable mirror. Actuators pitch is set to achieve high order correction in the visible wavelength.

  17. Determination of the Lithosphere-Asthenosphere Boundary (LAB) beneath the Nógrád-Gömör Volcanic Field by combined geophysical (magnetotellurics) and geochemical methods

    NASA Astrophysics Data System (ADS)

    Novák, Attila; Klébesz, Rita; Szabó, Csaba; Patkó, Levente; Liptai, Nóra; Kovács, Zoltán; Wesztergom, Viktor; Ádám, Antal; Lemperger, István; Kis, Árpád; Molnár, Csaba; Szendrői, Judit

    2014-05-01

    Understanding the fundamental role of LAB is substantial for the investigation of the geodynamic evolution of the Earth. The LAB depths can be estimated by different geophysical methods (seismology, magnetotellurics), however these depths are controversial. It has been emphasized in the literature that combined geophysical and geochemical approach may lead to better understanding of these depths. The magnetotellurics (MT) is very powerful method because it indicates the sudden increase in conductivity at the LAB. The mantle xenoliths (small fragments of the lithospheric mantle) provide the information to reconstruct their P-T paths. In the Carpathian-Pannon region (CPR) five, well-studied occurrences of mantle xenoliths-bearing Plio-Pleistocene alkali basalts are known, which makes the CPR a very promising area for investigating the inconsistency in the LAB estimates. As a test area Nógrád-Gömör Volcanic Field (NGVF) has been chosen. The host basalt erupted at the NGVF collected mantle xenoliths from a small volume of the upper mantle in a depth of about 40-50 km. The major element geochemistry of the studied xenoliths indicates that most of them represent common lherzolitic mantle, whereas others show strong wehrlitisation process. This metasomatism is supposed to be caused by a migrating mafic melt agent, resulting in the transformation of a large portion of lherzolite to wehrlite beneath the NGVF, possibly just below the crust mantle boundary. In aim to detect the LAB at the research area and find the correlation with petrologic and geochemical results we carried out MT deep soundings. The campaign contained 12 long period MT stations with 3-5 km average spacing along 60 km long profile SSE to NNW direction. This presentation summarizes the preliminary results of the combined geophysical and geochemical approaches to determine the LAB depths.

  18. Characterizing a large shear-zone with seismic and magnetotelluric methods: The case of the Dead Sea Transform

    USGS Publications Warehouse

    Maercklin, N.; Bedrosian, P.A.; Haberland, C.; Ritter, O.; Ryberg, T.; Weber, M.; Weckmann, U.

    2005-01-01

    Seismic tomography, imaging of seismic scatterers, and magnetotelluric soundings reveal a sharp lithologic contrast along a ???10 km long segment of the Arava Fault (AF), a prominent fault of the southern Dead Sea Transform (DST) in the Middle East. Low seismic velocities and resistivities occur on its western side and higher values east of it, and the boundary between the two units coincides partly with a seismic scattering image. At 1-4 km depth the boundary is offset to the east of the AF surface trace, suggesting that at least two fault strands exist, and that slip occurred on multiple strands throughout the margin's history. A westward fault jump, possibly associated with straightening of a fault bend, explains both our observations and the narrow fault zone observed by others. Copyright 2005 by the American Geophysical Union.

  19. A MATLAB GUI based algorithm for modelling Magnetotelluric data

    NASA Astrophysics Data System (ADS)

    Timur, Emre; Onsen, Funda

    2016-04-01

    The magnetotelluric method is an electromagnetic survey technique that images the electrical resistivity distribution of layers in subsurface depths. Magnetotelluric method measures simultaneously total electromagnetic field components such as both time-varying magnetic field B(t) and induced electric field E(t). At the same time, forward modeling of magnetotelluric method is so beneficial for survey planning purpose, for comprehending the method, especially for students, and as part of an iteration process in inverting measured data. The MTINV program can be used to model and to interpret geophysical electromagnetic (EM) magnetotelluric (MT) measurements using a horizontally layered earth model. This program uses either the apparent resistivity and phase components of the MT data together or the apparent resistivity data alone. Parameter optimization, which is based on linearized inversion method, can be utilized in 1D interpretations. In this study, a new MATLAB GUI based algorithm has been written for the 1D-forward modeling of magnetotelluric response function for multiple layers to use in educational studies. The code also includes an automatic Gaussian noise option for a demanded ratio value. Numerous applications were carried out and presented for 2,3 and 4 layer models and obtained theoretical data were interpreted using MTINV, in order to evaluate the initial parameters and effect of noise. Keywords: Education, Forward Modelling, Inverse Modelling, Magnetotelluric

  20. Magnetotelluric Data, Stable Distributions and Stable Regression

    NASA Astrophysics Data System (ADS)

    Chave, A. D.

    2013-12-01

    The author has noted for many years that the residuals from robust or bounded influence estimates of the magnetotelluric response function are systematically long tailed compared to a Gaussian or Rayleigh distribution. Consequently, the standard statistical model of a Gaussian core contaminated by a fraction of outlying data is not really valid. However, the typical result is an improvement on ordinary least squares, and has become standard in the electromagnetic induction community. A recent re-evaluation of the statistics of magnetotelluric response function estimation has shown that, in almost all cases, the residuals are alpha stable rather than Gaussian. Alpha stable distributions are characterized by four parameters: a shape parameter lying on (0, 2], a skewness parameter, a scale parameter and a location parameter, and cannot be expressed in closed form except for a few special cases. When the shape parameter is 2, the result is Gaussian, but when it is smaller the resulting distribution has infinite variance. Typical magnetotelluric residuals are alpha stable with a shape parameter lying between 1 and 2. This suggests that robust methods improve response function estimates by eliminating data corresponding to the largest stable residuals while leaving the bulk of the population alone. A better statistical approach is based on stable regression that directly accommodates the actual residual distribution without eliminating the most extreme ones. This paper will introduce such an algorithm, and illustrate its functionality with a variety of magnetotelluric data. Further work remains to produce a robust stable regression algorithm that will eliminate real outliers such as lightning strikes or instrument problems without affecting the bulk stable population. Stable distributions are intimately associated with fractional derivative physical processes. Since the Maxwell equations and the constitutive relations pertaining to the earth do not contain any fractional

  1. Determination of near-surface, crustal and lithospheric structures in the Canadian Precambrian Shield using time-domain electromagnetic and magnetotelluric methods

    NASA Astrophysics Data System (ADS)

    Wu, Xianghong

    Two electromagnetic methods were used to analyse the geoelectric structure of the subsurface of regions of the Precambrian Shield in Canada: the magnetotelluric (MT) and time-domain electromagnetic (TEM) methods. Magnetotelluric soundings were made at 60 sites in the southwestern Northwest Territories, Canada, along the LITHOPROBE SNORCLE Transect Corridor 1 and 1A, in the summer of 1996. The sites are located in southwestern Northwest Territories, Canada, between latitudes 60°--65°N and longitudes 110°--125°W, and cross the Archean Slave Province, the Proterozoic Buffalo Head, Great Bear Magmatic Arc, Hottah, Fort Simpson and Nahanni terranes, and the Great Slave Lake Shear Zone. Phanerozoic sedimentary rocks overlie the Proterozoic terranes. The main object of this project is to map the fracture zones and fresh/saline water interface in Precambrian granitic rocks using the surface TEM method. The TEM surveys were completed at Sites B, D, URL and A. A GEONICS PROTEM47 system with a 100 m transmitter loop was used. The data were collected for receiver offsets ranging from 0--280 m on four sides of transmitter loop. Analysis of the TEM and borehole log data indicates a basic three-layer structure: a thin conductive surface layer, a thick resistive second layer with an embedded conductive layer at some stations, and a conductive bottom layer. The results of this study show the TEM method can be used to investigate the fracture zones and groundwater salinity distribution in the Precambrian granitic rocks and contribute to site investigations for nuclear waste deposit. The TEM study in the Lac du Bonnet Batholith was successful in demonstrating the potential of the TEM methods in mapping groundwater salinity in granitic batholith. The PROTEM47 instrument, in combination with a 100 m transmitter loop, provides a suitable TEM system for mapping the resistivity structure of the Lac du Bonnet batholith down to a depth of 300--400 m. For deeper penetration and more

  2. Performance of preconditioned iterative and multigrid solvers in solving the three-dimensional magnetotelluric modeling problem using the staggered finite-difference method: a comparative study

    NASA Astrophysics Data System (ADS)

    Li, Gang; Zhang, Lili; Hao, Tianyao

    2016-02-01

    An effective solver for the large complex system of linear equations is critical for improving the accuracy of numerical solutions in three-dimensional (3D) magnetotelluric (MT) modeling using the staggered finite-difference (SFD) method. In electromagnetic modeling, the formed system of linear equations is commonly solved using preconditioned iterative relaxation methods. We present 3D MT modeling using the SFD method, based on former work. The multigrid solver and three solvers preconditioned by incomplete Cholesky decomposition—the minimum residual method, the generalized product bi-conjugate gradient method and the bi-conjugate gradient stabilized method—are used to solve the formed system of linear equations. Divergence correction for the magnetic field is applied. We also present a comparison of the stability and convergence of these iterative solvers if divergence correction is used. Model tests show that divergence correction improves the convergence of iterative solvers and the accuracy of numerical results. Divergence correction can also decrease the number of iterations for fast convergence without changing the stability of linear solvers. For consideration of the computation time and memory requirements, the multigrid solver combined with divergence correction is preferred for 3D MT field simulation.

  3. Geophysical characterization of areas prone to quick-clay landslides using radio-magnetotelluric and seismic methods

    NASA Astrophysics Data System (ADS)

    Wang, Shunguo; Malehmir, Alireza; Bastani, Mehrdad

    2016-05-01

    Landslides attributed to quick clays have not only considerable influences on surface geomorphology, they have caused delays in transportation systems, environmental problems and human fatalities, especially in Scandinavia and North America. If the subsurface distributions of quick clays are known, potential damages can be mitigated and the triggers of landslides can better be studied and understood. For this purpose, new radio-magnetotelluric (RMT) and seismic data were acquired in an area near the Göta River in southwest Sweden that contains quick clays and associated landslides. High-resolution data along 4 new lines, in total 3.8 km long, were acquired and merged with earlier acquired data from the site. Velocity and resistivity models derived from first breaks and RMT data were used to delineate subsurface geology, in particular the bedrock surface and coarse-grained materials that overlay the bedrock. The latter often are found underlying quick clays at the site. Comparably high-resistivity and sometimes high-velocity regions within marine clays are attributed to a combination of leached salt from marine clays or potential quick clays and coarse-grained materials. The resistivity and tomographic velocity models suggest a much larger role of the coarse-grained materials at the site than previously thought, but they also suggest two different scenarios for triggering quick-clay landslides at the site. These scenarios are related to the erosion of the riverbank, increased pore-pressure and surface topography when close to the river and human activity when away from the river and where bowl-shaped bedrock surrounds the sediments.

  4. Three-dimensional inversion of large-scale EarthScope magnetotelluric data based on the integral equation method: Geoelectrical imaging of the Yellowstone conductive mantle plume

    NASA Astrophysics Data System (ADS)

    Zhdanov, Michael S.; Smith, Robert B.; Gribenko, Alexander; Cuma, Martin; Green, Marie

    2011-04-01

    Interpretation of the EarthScope MT (magnetotelluric) data requires the development of a large-scale inversion method which can address two common problems of 3D MT inversion: computational time and memory requirements. We have developed an efficient method of 3D MT inversion based on an IE (integral equation) formulation of the MT forward modeling problem and a receiver footprint approach, implemented as a massively parallel algorithm. This method is applied to the MT data collected in the western United States as a part of the EarthScope project. As a result, we present one of the first 3D geoelectrical images of the upper mantle beneath Yellowstone revealed by this large-scale 3D inversion of the EarthScope MT data. These images show a highly conductive body associated with the tomographically imaged mantle plume-like layer of hot material rising from the upper mantle toward the Yellowstone volcano. The conductive body identified in these images is west-dipping in a similar way to a P-wave low-velocity body.

  5. An evaluation of the applicability of the telluric-electric and audio-magnetotelluric methods to mineral assessment on the Arabian Shield, Kingdom of Saudi Arabia

    USGS Publications Warehouse

    Flanigan, Vincent J.; Zablocki, Charles J.

    1984-01-01

    Feasibility studies of two electromagnetic methods were made in selected areas of the Jabal Hibshi (1:250,000) quadrangle, 26F, in the Kingdom of Saudi Arabia in March of 1983. The methods tested were the natural source-field telluricelectric and audio-magnetotelluric methods developed and extensively used in recent years by the U.S. Geological Survey in some of its domestic programs related to geothermal and mineral resource assessment. Results from limited studies in the Meshaheed district, the Jabal as Silsilah ring complex, and across a portion of the Raha fault zone clearly demonstrate the appropriateness of these sub-regional scale, reconnaissance-type studies to mineral resource assessment. The favorable results obtained are largely attributed to distinctive and large contrasts in the electrical resistivity of the major rock types encountered. It appears that the predominant controlling factor governing the rock resistivities is the amount of contained clay minerals. Accordingly, unaltered (specifically, non-argillic) igneous and metamorphic rocks have very high resistivities; metasedimentary rocks of the Murdama group that contain several percent clay minerals have intermediate values of resistivity; and highly altered rocks, containing abundant clay minerals, have very low values of resistivity. Water-filled fracture porosity may be a secondary, but important, factor in some settings. However, influences from variations in interstitial or intercrystalline, water-filled porosity are probably small because these types of porosity are generally low. It is reasonable to expect similar results in other areas within the Arabian Shield.

  6. Continuous profiling of magnetotelluric fields

    SciTech Connect

    Verdin, C.T.

    1991-05-01

    The magnetotelluric (MT) method of mapping ground electrical conductivity is traditionally based on measurement of the surface impedance at widely spaced stations to infer models of the subsurface through a suitable pseudo 1-D inverse or with linearized least-squares inversion for 2- or 3-D geoelectric media. It is well known that small near-surface inhomogeneities can produce spatial discontinuities in the measured electric fields over a wide frequency range and may consequently bias the impedance on a very local scale. Inadequate station spacing effectively aliases the electric field measurements and results in distortions that cannot be removed in subsequent processing or modelling. In order to fully exploit the benefits of magnetotellurics in complex geological environments, closely spaced measurements must be used routinely. This thesis entertains an analysis of MT data taken along continuous profiles and is a first step that will allow more encompassing 2-D sampling techniques to become viable in the years to come. The developments presented here are to a large extent motivated by the physical insight gained from low-contrast solutions to the forward MT problem. These solutions describe the relationship between a perturbation in the electrical conductivity of the subsurface and the ensuing perturbation of the MT response as the output of a linear system. Albeit strictly accurate in a limited subset of practical exploration problems, the linearized solutions allow one to pursue a model independent study of the response characteristics of MT data. In fact, these solutions yield simple expressions for 1-,2-, and 3-D resistivity models which are here examined in progressive sequence.

  7. Making Metadata Better with CMR and MMT

    NASA Technical Reports Server (NTRS)

    Gilman, Jason Arthur; Shum, Dana

    2016-01-01

    Ensuring complete, consistent and high quality metadata is a challenge for metadata providers and curators. The CMR and MMT systems provide providers and curators options to build in metadata quality from the start and also assess and improve the quality of already existing metadata.

  8. Classification of 5 DES supernovae by MMT

    NASA Astrophysics Data System (ADS)

    Challis, P.; Kirshner, R.; Mandel, K.; Avelino, A.; Foley, R. J.; Pan, Y.-C.; Casas, R.; Castander, F. J.; Desai, S.; Paech, K.; Smith, R. C.; Schubnell, M.; Kessler, R.; Lasker, J.; Scolnic, D.; Brout, D. J.; Gladney, L.; Sako, M.; Wolf, R. C.; Brown, P. J.; Krisciunas, K.; Suntzeff, N.; Nichol, R.; Papadopoulos, A.; Childress, M.; D'Andrea, C.; Smith, M.; Sullivan, M.; Maartens, R.; Gupta, R.; Kovacs, E.; Kuhlmann, S.; Spinka, H.; Ahn, E.; Finley, D. A.; Frieman, J.; Marriner, J.; Wester, W.; Aldering, G.; Kim, A. G.; Thomas, R. C.; Barbary, K.; Bloom, J. S.; Goldstein, D.; Nugent, P.; Perlmutter, S.

    2016-04-01

    We report optical spectroscopy of 5 supernovae discovered by the Dark Energy Survey (ATel #4668). The spectra (330-850nm) were obtained using the Blue Channel Spectrograph on the MMT. Object classification was performed using SNID (Blondin & Tonry, 2007, ApJ, 666, 1024) and superfit (Howell et al, 2005, ApJ, 634, 119), the details of which are reported in the table below.

  9. The MMT-POL Instrument Control System

    NASA Astrophysics Data System (ADS)

    Warner, C.; Packham, C.; Jones, T. J.; Varosi, F.; Eikenberry, S. S.; Dewahl, K.; Krejny, M.

    2011-07-01

    Instrument control system (ICS) suites are a continually evolving class of software packages that are highly dependent upon the design choices and application programming interfaces (APIs) of the observatory control system (OCS), as well as the hardware choices for motors and electronics. We present the ICS for MMT-POL, a 1-5 μm polarimeter for the MMT telescope, in the context of being a transitional step between the software packages developed for facility class instruments at the University of Florida (UF), such as Flamingos-II and CanariCam, and in preparation for 30 m-class instruments. Our goals for improving ICS suites are to make them (a) portable (compile once, run anywhere), (b) highly modular and extensible (through the re-use of common libraries), (c) multi-threaded (to allow multiple tasks to be performed in parallel), (d) smart, and (e) easy to use and maintain. An ICS should also be well-defined and use mature languages (we choose Java and Python) and common standards (such as XML and the FITS file format). We also note that as hardware moves away from serial communications to ethernet, the use of TCP sockets makes communication faster and easier. Below, we present our design choices for the MMT-POL ICS and discuss our reasons for these choices and potential issues that must be addressed for future ICS suites ready for thirty meter class instruments.

  10. Early Results of a Magnetotelluric Survey in the Nechako Sedimentary Basin, B.C., Designed to Assess the Method as a Tool in Oil and Gas Exploration

    NASA Astrophysics Data System (ADS)

    Spratt, J. E.; Craven, J. A.

    2008-12-01

    Magnetotelluric (MT) data was collected in the fall of 2007 within the Nechako Basin, B.C., Canada, to evaluate the usefulness of the technique for hydrocarbon exploration and to characterize the structure of the basin. The Mesozoic Nechako Basin is located within the Intermontane Belt of the Canadian Cordillera and includes overlapping sedimentary sequences deposited in response to terrane amalgamation to the western edge of ancestral North America. Beginning in the Late Cretaceous, regional transcurrent faulting and associated east-west extension were accompanied by the extrusion of basaltic lava that forms a laterally variable sheet covering much of the basin. The potential for hydrocarbons has been noted within several interior basins of British Columbia however, an important impediment to hydrocarbon exploration is the inability of traditional geophysical methods to see through the volcanic sequences. As the MT method is not hampered by these volcanics, a survey consisting of 734 combined high frequency and broadband sites was undertaken. Strike analysis shows lateral changes in the preferred geoelectric strike direction at periods between 0.1 and 10s, suggesting that localized structure is influencing the strike angle. Two-dimensional models along in the vicinity of Nazco, B.C. reveal a shallow conductive layer that likely represents the sedimentary packages of the Nechako Basin overlying a resistive layer that is interpreted as the crystalline basement rocks. Focused inversions illustrate a higher resolution of the shallow features within the Nechako sediments and reveal complex geologic structures. These models indicate that the method is capable of both penetrating and imaging the surface volcanics where they are thick. Distinct variations in the shallow conductive layer as well as the presence of resistive structures that break up the lateral continuity of the conductor are observed. These structures are an indication of fault systems that carry the

  11. Update of MmtDB: a Metazoa mitochondrial DNA variants database.

    PubMed Central

    Attimonelli, M; Calò, D; De Montalvo, A; Lanave, C; Sasanelli, D; Tommaseo Ponzetta, M; Saccone, C

    1998-01-01

    The present paper describes the improvements in MmtDB, a specialised database designed to collect Metazoa mitochondrial DNA variants. Priority in the data collection has been given to Metazoa for which a large amount of variants is available, e.g., for humans. Starting from the sequences available in the Nucleotide Sequence Databases, the redundant sequences have been removed and new sequences from other sources have been added. Value-added information is associated to each variant sequence, e.g., analysed region, experimental method, tissue and cell lines, population data, sex, age, family code and information about the variation events (nucleotide position, involved gene, restriction site gain or loss). Cross-references are introduced to the EMBL Data Library, as well as an internal cross-referencing among MmtDB entries according to tissual, heteroplasmic, familiar and aplotypical correlation. Furthermore MmtDB has a new section, AMmtDB: Aligned Metazoan mitochondrial biosequences. MmtDB can be accessed through the World Wide Web at URL http://WWW.ba.cnr.it/[symbol: see text]areamt08/MmtDBWWW.htm PMID:9399815

  12. STS-114: Discovery Post MMT Briefing

    NASA Technical Reports Server (NTRS)

    2005-01-01

    Wayne Hale, Space Shuttle Deputy Program Manager and Terri Murphy, Space Shuttle Imagery Integration Manager are seen in this post Mission Management Team (MMT) briefing. Hale begins with showing a video that was recovered from the Solid Rocket Booster (SRB) looking at the external tank during ascent. Pictures of the RH Nose Landing Gear Damage (NLGD), Protruding gap filler near chine and protruding gap fillers are shown. Terri Murphy talks about the imagery from debris, integrated simulations and radar data collected from the launch. Hale answers questions from the news media about the location of the gap fillers, possible EVA to remove the gap fillers and the thermal protection system.

  13. STS-121: Discovery Launch Postponement MMT Briefing

    NASA Technical Reports Server (NTRS)

    2006-01-01

    Bruce Buckingham from NASA Public Affairs introduces the panel who consist of: John Shannon, MMT chairman JSC; Mike Leinbach, NASA Launch Director; and 1st Lieutenant Kaleb Nordren, USAF 45th Weather Squadron. An opening statement is given from John Shannon on the postponement of the launch due to thunderstorms. Mike Leinbach also elaborates on the weather and talks about scrubbing two hours early, draining the vehicle, and reloading the hydrogen for the fuel cells for a possible launch attempt on Tuesday morning. Norden gives his weather forecast for Tuesday and Wednesday. Questions from the media on launch attempts, weather, and the cost of the scrub are addressed.

  14. Regional magnetotelluric surveys in hydrocarbon exploration, Parana' Basin, Brazil

    SciTech Connect

    Stanley, W.D.; Ohofugi, W.; Saad, A.R.

    1985-03-01

    The magnetotelluric geophysical method has been used effectively as a hydrocarbon exploration tool in the intracratonic Parana basin of South America. The 1-2 km thick surface basalts and buried diabase sills pose no problem for the magnetotelluric method because the natural electromagnetic fields used as the energy source pass easily through the basalt. Data for the regional study were taken on six profiles with soundings spaced 8 to 15 km apart. The magnetotelluric sounding data outline a linear uplift known as the Ponta Grossa arch. This major structural feature cuts across the northeast-trending intracratonic basin almost perpendicularly, and is injected with numerous diabase dikes. In the survey area, MT interpretations show that basalts have aggregate thicknesses of as much as 2 km (6,600 ft), and basement may be as much as 6 km (20,000 ft) below the surface. Over most of the basin, the basalts are covered by Upper Cretaceous to Holocene continental sediments of a few hundred meters thickness and are underlain by 2 to 4 km (6,600 to 13,100 ft) thick Paleozoic sediments with possible hydrocarbon potential. Significant electrical contrasts occur between the Permian sediments and older units, so that magnetotelluric measurements can give an indication of the regional thickness of the Permian and younger sediments to aid in interpreting hydrocarbon migration patterns and possible trap areas.

  15. Enhanced separation performance of PVDF/PVP-g-MMT nanocomposite ultrafiltration membrane based on the NVP-grafted polymerization modification of montmorillonite (MMT).

    PubMed

    Wang, Panpan; Ma, Jun; Wang, Zhenghui; Shi, Fengmei; Liu, Qianliang

    2012-03-13

    A novel hydrophilic nanocomposite additive (PVP-g-MMT), coupling of hydrophilic modifier, self-dispersant, and pore-forming agent (porogen), was synthesized by the surface modification of montmorillonite (MMT) with N-vinylpyrrolidone (NVP) via "grafting from" polymerization in the presence of H(2)O(2)-NH(3)·H(2)O as the initiator, and then the nanocomposite membrane of poly(vinylidene fluoride) (PVDF) and PVP-g-MMT was fabricated by wet phase inversion onto clean glass plates. The existence and dispersion of PVP-g-MMT had a great role on structures, morphologies, surface composition, and chemistry of the as-prepared nanocomposite membranes confirmed by varieties of spectroscopic and microscopic characterization techniques, all of which were the correlated functions of PVP-g-MMT content in casting solution. By using the dead-end filtration of protein aqueous solution, the performance of the membrane was evaluated. It was seen that all of the nanocomposite membranes showed obvious improvement of water flux and proper BSA rejection ratio, compared to the control PVDF membrane. Meanwhile, dynamic BSA fouling resistance and flux recovery properties were also greatly enhanced due to the changes of surface hydrophilicity and morphologies. All the experimental results indicated that the as-prepared PVDF nanocomposite membranes showed better separation performances than the control PVDF membrane. Hopefully, the demonstrated method of hydrophilic nanocomposite additive synthesis would be applied for commonly hydroxyl group-containing inorganic nanoparticles, which was favorable to fabricate hydrophilic nanoparticle-enhanced polymer membranes for water treatment. PMID:22376185

  16. STS-114: Discovery Post MMT Briefing

    NASA Technical Reports Server (NTRS)

    2005-01-01

    Wayne Hale, Space Shuttle Deputy Program Manager, is presented in this STS-114 Discovery Post Mission Management Team (MMT) briefing. He begins by talking about obtaining clearance from the Reinforced Carbon-Carbon (RCC) material. He then describes the supplies such as eleven water containers and the transfer of 50 additional pounds of Oxygen to the International Space Station. Hale presents a video of a billowed thermal blanket next to the commander's window on the port side of the Space Shuttle Discovery that seems to be of some concern. He answers questions from the news media about the dimensions of this blanket, and the dangers of getting close to this blanket during the Extravehicular Activity (EVA) to repair the gap fillers.

  17. Performance of the Multiple Mirror Telescope (MMT). II Mechanical properties of the MMT

    NASA Astrophysics Data System (ADS)

    Davison, W.; Ulich, B. L.

    1982-10-01

    Attention is given to innovative features of the Multiple Mirror Telescope (MMT) alt-azimuth mount and Optical Support Structure (OSS). The repositioning of a single azimuth drive system motor has allowed the azimuth resonant frequency to be increased from 2.2 to 3.0 Hz, and the addition of two more drives is projected to increase frequency to 4.1 Hz .The intrincate truss structure of the OSS has several variable area, or tuning, members that can compensate for gravitational flexure. Such adjustments, together with thermal radiation shielding, have allowed the six telescopes comprising the MMT to be passively aligned to 20 arcsec. Attention is also given to the friction measured for the aximuth ball bearings and drives.

  18. New approaches to estimation of magnetotelluric parameters

    SciTech Connect

    Egbert, G.D.

    1991-01-01

    Fully efficient robust data processing procedures were developed and tested for single station and remote reference magnetotelluric (Mr) data. Substantial progress was made on development, testing and comparison of optimal procedures for single station data. A principal finding of this phase of the research was that the simplest robust procedures can be more heavily biased by noise in the (input) magnetic fields, than standard least squares estimates. To deal with this difficulty we developed a robust processing scheme which combined the regression M-estimate with coherence presorting. This hybrid approach greatly improves impedance estimates, particularly in the low signal-to-noise conditions often encountered in the dead band'' (0.1--0.0 hz). The methods, and the results of comparisons of various single station estimators are described in detail. Progress was made on developing methods for estimating static distortion parameters, and for testing hypotheses about the underlying dimensionality of the geological section.

  19. Stochastic Inversion of 2D Magnetotelluric Data

    SciTech Connect

    Chen, Jinsong

    2010-07-01

    The algorithm is developed to invert 2D magnetotelluric (MT) data based on sharp boundary parametrization using a Bayesian framework. Within the algorithm, we consider the locations and the resistivity of regions formed by the interfaces are as unknowns. We use a parallel, adaptive finite-element algorithm to forward simulate frequency-domain MT responses of 2D conductivity structure. Those unknown parameters are spatially correlated and are described by a geostatistical model. The joint posterior probability distribution function is explored by Markov Chain Monte Carlo (MCMC) sampling methods. The developed stochastic model is effective for estimating the interface locations and resistivity. Most importantly, it provides details uncertainty information on each unknown parameter. Hardware requirements: PC, Supercomputer, Multi-platform, Workstation; Software requirements C and Fortan; Operation Systems/version is Linux/Unix or Windows

  20. Stochastic Inversion of 2D Magnetotelluric Data

    Energy Science and Technology Software Center (ESTSC)

    2010-07-01

    The algorithm is developed to invert 2D magnetotelluric (MT) data based on sharp boundary parametrization using a Bayesian framework. Within the algorithm, we consider the locations and the resistivity of regions formed by the interfaces are as unknowns. We use a parallel, adaptive finite-element algorithm to forward simulate frequency-domain MT responses of 2D conductivity structure. Those unknown parameters are spatially correlated and are described by a geostatistical model. The joint posterior probability distribution function ismore » explored by Markov Chain Monte Carlo (MCMC) sampling methods. The developed stochastic model is effective for estimating the interface locations and resistivity. Most importantly, it provides details uncertainty information on each unknown parameter. Hardware requirements: PC, Supercomputer, Multi-platform, Workstation; Software requirements C and Fortan; Operation Systems/version is Linux/Unix or Windows« less

  1. On the statistics of magnetotelluric rotational invariants

    NASA Astrophysics Data System (ADS)

    Chave, Alan D.

    2014-01-01

    The statistical properties of the Swift skew, the phase-sensitive skew and the WAL invariants I1-I7 and Q are examined through analytic derivation of their probability density functions and/or simulation based on a Gaussian model for the magnetotelluric response tensor. The WAL invariants I1-I2 are shown to be distributed as a folded Gaussian, and are statistically well behaved in the sense that all of their moments are defined. The probability density functions for Swift skew, phase-sensitive skew and the WAL invariants I3-I4, I7 and Q are derived analytically or by simulation, and are shown to have no moments of order 2 or more. Since their support is semi-infinite or infinite, they cannot be represented trigonometrically, and hence are inconsistent with a Mohr circle interpretation. By contrast, the WAL invariants I5-I6 are supported on [ - 1, 1], and are inferred to have a beta distribution based on analysis and simulation. Estimation of rotational invariants from data is described using two approaches: as the ratio of magnetotelluric responses that are themselves averages, and as averages of section-by-section estimates of the invariant. Confidence intervals on the former utilize either Fieller's theorem, which is preferred because it is capable of yielding semi-infinite or infinite confidence intervals, or the less accurate delta method. Because section-by-section averages of most of the rotational invariants are drawn from distributions with infinite variance, the classical central limit theorem does not pertain. Instead, their averaging is accomplished using the median in place of the mean for location and an order statistic model to bound the confidence interval of the median. An example using real data demonstrates that the ratio of averages approach has serious systematic bias issues that render the result physically inconsistent, while the average of ratios result is a smooth, physically interpretable function of period, and is the preferred approach.

  2. Magnetotelluric pilot study in the Rio Grande Rift, southwest USA

    NASA Astrophysics Data System (ADS)

    Feucht, D. W.; Bedrosian, P. A.; Sheehan, A. F.

    2012-12-01

    A magnetotelluric (MT) pilot study consisting of approximately 25 stations distributed in and around the Rio Grande Rift of the southwest United States was carried out in the summer of 2012. Both broadband (100 Hz to 1000 s) and long-period (up to 10 000 s) MT data were collected across two profiles that run perpendicular to the rift axis near Denver, Colorado and Taos, New Mexico, respectively. Time-domain EM data was also collected at each site to account for galvanic distortion in the near-surface. The tectonic forces and rheologic properties behind the initiation and propagation of the rift are poorly understood. Surface mapping of volcanism, normal faulting and sedimentary basins reveals a narrow band of crustal deformation confined to a region in close proximity to the rift axis while geophysical results suggest that deformation is distributed across a much broader and deeper region of the lithosphere. In particular, seismic tomography shows low seismic wave speeds into the lower crust and upper mantle. The magnetotelluric technique is a well-proven passive electromagnetic method that allows for the detection of apparent resistivity at a wide range of depth scales. Complimenting the seismic results with MT data will provide important new information on the geologic and geophysical properties that control the rifting process in this low-strain rate environment. Properties to which the MT method is particular sensitive include temperature, fluid content, and mineral alteration. Preliminary results from this most recent survey are encouraging, showing good data quality up to 10 000 s. In an important precursor to full 2D modeling, the magnetotelluric phase tensor has been used to assess the dimensionality of the electrical resistivity structure at depth. This pilot study provides proof of concept for a much larger magnetotelluric experiment planned to take place in the Rio Grande Rift in 2013.

  3. Cooperative inversion of magnetotelluric and seismic data sets

    NASA Astrophysics Data System (ADS)

    Markovic, M.; Santos, F.

    2012-04-01

    Cooperative inversion of magnetotelluric and seismic data sets Milenko Markovic,Fernando Monteiro Santos IDL, Faculdade de Ciências da Universidade de Lisboa 1749-016 Lisboa Inversion of single geophysical data has well-known limitations due to the non-linearity of the fields and non-uniqueness of the model. There is growing need, both in academy and industry to use two or more different data sets and thus obtain subsurface property distribution. In our case ,we are dealing with magnetotelluric and seismic data sets. In our approach,we are developing algorithm based on fuzzy-c means clustering technique, for pattern recognition of geophysical data. Separate inversion is performed on every step, information exchanged for model integration. Interrelationships between parameters from different models is not required in analytical form. We are investigating how different number of clusters, affects zonation and spatial distribution of parameters. In our study optimization in fuzzy c-means clustering (for magnetotelluric and seismic data) is compared for two cases, firstly alternating optimization and then hybrid method (alternating optimization+ Quasi-Newton method). Acknowledgment: This work is supported by FCT Portugal

  4. Hectochelle: A Multiobject Optical Echelle Spectrograph for the MMT

    NASA Astrophysics Data System (ADS)

    Szentgyorgyi, Andrew; Furesz, Gabor; Cheimets, Peter; Conroy, Maureen; Eng, Roger; Fabricant, Daniel; Fata, Robert; Gauron, Thomas; Geary, John; McLeod, Brian; Zajac, Joseph; Amato, Stephen; Bergner, Henry; Caldwell, Nelson; Dupree, Andrea; Goddard, Richard; Johnston, Everett; Meibom, Soeren; Mink, Douglas; Pieri, Mario; Roll, John; Tokarz, Susan; Wyatt, William; Epps, Harland; Hartmann, Lee; Meszaros, Szabolcz

    2011-10-01

    The Hectochelle is an optical band, fiber-fed, multiobject echelle spectrograph deployed at the MMT Observatory on Mount Hopkins, Arizona. The optical fibers that feed the Hectochelle are positioned by the Hectospec robot positioner on the MMT f/5 focal surface, and the Hectochelle shares an optical fiber feed system with the Hectospec, a moderate-dispersion spectrograph that is collocated with the Hectochelle. Hectochelle can record up to 240 spectra simultaneously at a resolution of 38,000. Spectra cover a single diffractive order that is approximately 150 Å wide. The total potential operating passband of the Hectochelle extends from 3800 Å to 9000 Å. Operated in conjunction with the MMT f/5 secondary, the MMT wide-field corrector, and the atmospheric dispersion compensator, the patrol field is 1° in diameter and the individual fiber slits are 1.5'' in diameter. The throughput of the combined telescope, fiber feed, and spectrograph is measured to be 6.1% at 5275 Å, exclusive of atmospheric extinction. A 20 minute observation of a V = 15 F-type star yields a signal-to-noise ratio of 35 per resolution element. Hectochelle had first light 2003 December 4 and continues to be operated at the MMT today.

  5. Singular value decomposition in magnetotelluric sounding data processing

    SciTech Connect

    Shengjie, S. )

    1991-01-01

    In this paper singular value decomposition method, a method for magnetotelluric sounding data processing, is recommended minutely; and its real number operation process is derived. For analysis, this method decomposes data matrix into signal matrix and noise matrix. It may give least squares estimation of response function, performs quantitative analysis of signal and noise to calculate S/N ratio, and offers the estimated variance of the response function. Theoretical calculation shows that this method is reliable and effective in suppressing noise, estimating response function, and analyzing noise and variance.

  6. Introducing Python tools for magnetotellurics: MTpy

    NASA Astrophysics Data System (ADS)

    Krieger, L.; Peacock, J.; Inverarity, K.; Thiel, S.; Robertson, K.

    2013-12-01

    Within the framework of geophysical exploration techniques, the magnetotelluric method (MT) is relatively immature: It is still not as widely spread as other geophysical methods like seismology, and its processing schemes and data formats are not thoroughly standardized. As a result, the file handling and processing software within the academic community is mainly based on a loose collection of codes, which are sometimes highly adapted to the respective local specifications. Although tools for the estimation of the frequency dependent MT transfer function, as well as inversion and modelling codes, are available, the standards and software for handling MT data are generally not unified throughout the community. To overcome problems that arise from missing standards, and to simplify the general handling of MT data, we have developed the software package "MTpy", which allows the handling, processing, and imaging of magnetotelluric data sets. It is written in Python and the code is open-source. The setup of this package follows the modular approach of successful software packages like GMT or Obspy. It contains sub-packages and modules for various tasks within the standard MT data processing and handling scheme. Besides pure Python classes and functions, MTpy provides wrappers and convenience scripts to call external software, e.g. modelling and inversion codes. Even though still under development, MTpy already contains ca. 250 functions that work on raw and preprocessed data. However, as our aim is not to produce a static collection of software, we rather introduce MTpy as a flexible framework, which will be dynamically extended in the future. It then has the potential to help standardise processing procedures and at same time be a versatile supplement for existing algorithms. We introduce the concept and structure of MTpy, and we illustrate the workflow of MT data processing utilising MTpy on an example data set collected over a geothermal exploration site in South

  7. The characterizations of rheological, electrokinetical and structural properties of ODTABr/MMT and HDTABr/MMT organoclays

    SciTech Connect

    Isci, S. Uslu, Y.O.; Ece, O.I.

    2009-05-15

    In the present paper, we have investigated as a function of surfactant concentration the rheological (yield value, plastic viscosity) and electrokinetic (mobility, zeta potential) properties of montmorillonite (MMT) dispersions. The influence of surfactants (Octadeccyltrimethylammonium bromide, ODTABr and Hexadecyltrimethylammonium bromide, HDTABr) on dispersions of Na-activated bentonite was evaluated by rheological and electrokinetic measurements, and X-ray diffraction (XRD) studies. The interactions between clay minerals and surfactants in water-based Na-activated MMT dispersions (2 wt.%) were examined in detail using rheologic parameters, such as viscosity, yield point, apparent and plastic viscosity, hysteresis area, and electrokinetic parameters of mobility and zeta potentials, and XRD also analyses helped to determine swelling properties of d-spacings. MMT and organoclay dispersions showed Bingham Plastic flow behavior. The zeta potential measurements displayed that the surfactant molecules hold on the clay particle surfaces and the XRD analyses displayed that they get into the basal layers.

  8. A final report on computed magneto-telluric curves for hypothetical models of crustal structure

    USGS Publications Warehouse

    Pritchard, J.I.

    1965-01-01

    Several mathematical models were investigated to determine the capa-bilities of the magneto-telluric method for determining the resistivity structure of the earth's crust. The model parameters were based on the crust model proposed by Keller (1963). The mathematical technique used was developed by Cagniard (1953). The investigations indicate that a three-layer model approximation of the crust and mantle is the most detailed model warranted in inter-preting the information provided by the magneto-telluric method about the lower crust. Only the thickness of the lower crust can be determined, and not the resistivity.

  9. New approaches to estimation of magnetotelluric parameters

    SciTech Connect

    Egbert, G.D. . Coll. of Oceanography); Booker, J.R. )

    1990-01-01

    This document proposed the development and application of some new statistical techniques for improving the collection and analysis of wide-band magnetotelluric (MT) data. The principle goal of our work is to develop and implement fully automatic single station and remote reference impedance estimation schemes which are robust, unbiased and statistically efficient. The initial proposal suggested several extensions to the regression M-estimates to better allow for non-stationary and non-Gaussian noise in both electric and magnetic field channels (measured at one or more simultaneous stations). A second goal of the proposal was to develop formal, reliable procedures for estimating undistorted 2-d strike directions and to develop statistics for assessing the validity of the 2-d assumption that are unaffected by near surface static distortion effects. To test and validate the methods, working with data selected from a series of over 200 wide-band MT sites was proposed. For the current budget period, setting up a data base, and completing development and initial testing of the single station and remote reference methods outlined in the proposal is suggested. 8 refs., 13 figs.

  10. Two and three dimensional magnetotelluric inversion

    SciTech Connect

    Booker, J.R.

    1994-07-01

    Improved imaging of underground electrical structure has wide practical importance in exploring for groundwater, mineral and geothermal resources, and in characterizing oil fields and waste sites. Because the electromagnetic inverse problem for natural sources is generally multi-dimensional, most imaging algorithms saturate available computer power long before they can deal with complete data sets. We have developed an algorithm to directly invert large multi-dimensional magnetotelluric data sets that is orders of magnitude faster than competing methods. In the past year, we have extended the two- dimensional (2D) version to permit incorporation of geological constraints, have developed ways to assess model resolution and have completed work on an accurate and fast three-dimensional (3D) forward algorithm. We are proposing to further enhance the capabilities of the 2D code and to incorporate the 3D forward code in a fully 3D inverse algorithm. Finally, we will embark on an investigation of related EM imaging techniques which may have the potential for further increasing resolution.

  11. Commissioning results of MMT-POL: the 1-5um imaging polarimeter leveraged from the AO secondary of the 6.5m MMT

    NASA Astrophysics Data System (ADS)

    Packham, C.; Jones, T. J.; Warner, C.; Krejny, M.; Shenoy, D.; Vonderharr, T.; Lopez-Rodriguez, E.; DeWahl, K.

    2012-09-01

    MMT-POL is an adaptive optics optimized imaging polarimeter designed for use at the 6.5m MMT. By taking full advantage of the adaptive optics secondary mirror of the MMT, this polarimeter offers diffraction-limited polarimetry with very low instrumental polarization and minimal thermal background. MMT-POL permits observations as diverse as protoplanetary discs, comets, red giant winds, (super)novae and ejecta, galaxies, and AGN. We report on the initial on-sky commissioning results of the instrument including a description of the instrument.

  12. Semiautomatic and Automatic Cooperative Inversion of Seismic and Magnetotelluric Data

    NASA Astrophysics Data System (ADS)

    Le, Cuong V. A.; Harris, Brett D.; Pethick, Andrew M.; Takam Takougang, Eric M.; Howe, Brendan

    2016-09-01

    Natural source electromagnetic methods have the potential to recover rock property distributions from the surface to great depths. Unfortunately, results in complex 3D geo-electrical settings can be disappointing, especially where significant near-surface conductivity variations exist. In such settings, unconstrained inversion of magnetotelluric data is inexorably non-unique. We believe that: (1) correctly introduced information from seismic reflection can substantially improve MT inversion, (2) a cooperative inversion approach can be automated, and (3) massively parallel computing can make such a process viable. Nine inversion strategies including baseline unconstrained inversion and new automated/semiautomated cooperative inversion approaches are applied to industry-scale co-located 3D seismic and magnetotelluric data sets. These data sets were acquired in one of the Carlin gold deposit districts in north-central Nevada, USA. In our approach, seismic information feeds directly into the creation of sets of prior conductivity model and covariance coefficient distributions. We demonstrate how statistical analysis of the distribution of selected seismic attributes can be used to automatically extract subvolumes that form the framework for prior model 3D conductivity distribution. Our cooperative inversion strategies result in detailed subsurface conductivity distributions that are consistent with seismic, electrical logs and geochemical analysis of cores. Such 3D conductivity distributions would be expected to provide clues to 3D velocity structures that could feed back into full seismic inversion for an iterative practical and truly cooperative inversion process. We anticipate that, with the aid of parallel computing, cooperative inversion of seismic and magnetotelluric data can be fully automated, and we hold confidence that significant and practical advances in this direction have been accomplished.

  13. Audio-magnetotelluric data collected in the area of Beatty, Nevada

    SciTech Connect

    Williams, J.M.

    1998-11-01

    In the summer of 1997, electrical geophysical data was collected north of Beatty, Nevada. Audio-magnetotellurics (AMT) was the geophysical method used to collect 16 stations along two profiles. The purpose of this data collection was to determine the depth to the alluvial basement, based upon the needs of the geologists requesting the data.

  14. Fast and stable two-dimensional inversion of magnetotelluric data

    NASA Astrophysics Data System (ADS)

    de Lugao, Patricia Pastana

    1997-07-01

    The two-dimensional (2-D) magnetotelluric (MT) inverse problem still poses difficult challenges in spite of efforts to develop fast and efficient methods for its solution. In this work, a new approach based on regularization theory and the quasi-analytic calculation of the Frechet derivatives is presented. For the forward solution, a fast and efficient finite difference formulation to the solution of the MT equations in both transverse electric (TE) and transverse magnetic (TM) modes based on the balance method is used. The Frechet derivative matrix is obtained as a solution to simple forward and back substitution of the LU decomposed matrix of coefficients from the forward problem utilizing the principle of reciprocity. The magnetotelluric inverse problem is ill-posed. In order to constrain the solution to a set of acceptable models, Tikhonov regularization is applied based on the minimization of a parametric functional. The regularized cojugate gradient method is then utilized to minimize the parametric functional. Inversion results of a set of synthetic data and of a set of CSAMT data from Kennecott Exploration show that the method is fast, stable and produces geologically reasonable models.

  15. Improving of electrical channels for magnetotelluric sounding instrumentation

    NASA Astrophysics Data System (ADS)

    Prystai, A. M.; Pronenko, V. O.

    2015-07-01

    The study of the deep structure of the Earth's crust is of great interest for both applied (e.g. mineral exploration) and scientific research. For this the electromagnetic (EM) studies which enable one to construct the distribution of electrical conductivity in the Earth's crust are of great use. The most common method of EM exploration is magnetotelluric sounding (MT). This passive method of research uses a wide range of natural geomagnetic variations as a powerful source of electromagnetic induction in the Earth, producing telluric current variations there. It includes the measurements of variations of natural electric and magnetic fields in orthogonal directions at the surface of the Earth. By this, the measurements of electric fields are much more complicated metrological processes, and, namely, they limit the precision of MT prospecting. This is especially complicated at deep sounding when measurements of long periods are of interest. The increase in the accuracy of the electric field measurement can significantly improve the quality of MT data. Because of this, the development of a new version of an instrument for the measurements of electric fields at MT - both electric field sensors and the electrometer - with higher levels relative to the known instrument parameter level - was initiated. The paper deals with the peculiarities of this development and the results of experimental tests of the new sensors and electrometers included as a unit in the long-period magnetotelluric station LEMI-420 are given.

  16. CuO-MMT nanocomposite: effective photocatalyst for the discoloration of methylene blue in the absence of H2O2

    NASA Astrophysics Data System (ADS)

    Sohrabnezhad, Sh.; Pourahmad, A.; Salavatiyan, T.

    2016-02-01

    Copper oxide (CuO) nanoparticles are of particular interest because of their interesting properties and promising applications in photocatalysis and purification of water. In this work, CuO-montmorillonite (CuO-MMT) nanocomposite was synthesized by a thermal decomposition method and characterized by diffuse reflectance spectroscopy, X-ray diffraction, Fourier transform infrared spectroscopy and transmission electron microscopy. The resultant particles were nearly spherical, and particle size in MMT was in the range of ˜3-5 nm. The powder X-ray reflection patterns indicate that MMT has a d-spacing higher (1.22 nm) than CuO-MMT nanocomposite (0.97 nm). The shrinkage probably is related to the conformation of CuO nanoparticles on the clay surface. The diffuse reflectance spectrum of CuO-MMT showed band around 340-360 nm corresponding to presence of [Cu-O-Cu] n -type clusters over the support surface. The band gaps of the resulting CuO nanoparticles and CuO-MMT nanocomposite were widened from 1.70 to 1.80 eV for an indirect allowed band gap and from 3.70 to 3.82 eV for a direct allowed inter band transition owing to the quantum size effect, respectively. The nanocomposite exhibited an enhanced and stable photoactivity for the discoloration of methylene blue (MB) aqueous solution under visible light. The result showed that MB discoloration was observed after 20 min light irradiation in the absence of H2O2. The several parameters were examined, such as the catalyst amount, pH and initial concentration of MB. The mechanism of separation of the photogenerated electrons and holes of the CuO-MMT nanocomposite was discussed.

  17. STS-114: Post Launch MMT Briefing

    NASA Technical Reports Server (NTRS)

    2005-01-01

    Bill Parsons, Space Shuttle Program Manager, and Wayne Hill, Deputy Manager of the Space Shuttle Program, and Chair of the Mission Management Team talks about the flight day 2 of the Discovery. Bill noted that flight operations are extremely going on well. He also explained an unexpected debris event on a power ramp little ways down where LH2 ramp begins. Before flight and based from technical data, slight modifications were done on the power ramp to ensure safety of return to flight. Bill also noted that STS-114 is a test flight; all data collected and brought back by the crew will be analyzed to ensure that all information needed is sufficient to work on faults and defects and to make appropriate repairs. Wayne discussed on flight safety. He emphasized the need to thoroughly inspect the thermal protection system of the Orbiter to ensure safe entry. Inspection of still photographs from the ISS and the boom sensor system scan are the primary means to understand engineering data in terms of the immediate flight safety. He also reported accomplishments for the day such as survey of the Orbiter boom system, all the wing leading edge, RCC panels and the nose cap, to make sure these are in good shape and working well, and re-emphasized that these are primary methods to clear the thermal protection system of the Orbiter to prove that it is safe to come home on this flight.

  18. Dimensionality imprint of electrical anisotropy in magnetotelluric responses

    NASA Astrophysics Data System (ADS)

    Martí, A.; Queralt, P.; Ledo, J.; Farquharson, C.

    2010-10-01

    Dimensionality analysis of magnetotelluric data is a common procedure for inferring the main properties of the geoelectric structures of the subsurface such as the strike direction or the presence of superficial distorting bodies, and enables the most appropriate modeling approach (1D, 2D or 3D) to be determined. Most of the methods currently used assume that the electrical conductivity of individual parts of a structure is isotropic, although some traces of anisotropy in data responses can be recognized. In this paper we investigate the imprints of anisotropic media responses in dimensionality analysis using rotational invariants of the magnetotelluric tensor. We show results for responses generated from 2D synthetic anisotropic models and for field data that have been interpreted as showing the effects of electrical anisotropy in parts of the subsurface structure. As a result of this study we extend the WAL dimensionality criteria to include extra conditions that allow anisotropic media to be distinguished from 2D isotropic ones. The new conditions require the analysis of the strike directions obtained and take into account the overall behavior of different sites in a survey.

  19. The Lithospheric Structure of Southern Africa from Magnetotelluric Sounding

    NASA Astrophysics Data System (ADS)

    Evans, R. L.; Jones, A. G.; Atekwana, E. A.

    2014-12-01

    Measurements of mantle electrical conductivity, made through the magnetotelluric method, offer considerable insight into the structure of cratonic lithosphere. A particularly expansive data set has been collected in Southern Africa, started through the Southern Africa Magnetotelluric Experiment (SAMTEX) experiment, now continuing north through Zambia as part of the Project for Rift Initiation Development and Evolution (PRIDE) experiment. The combined data set highlights large variability in lithospheric structure that broadly correlates with surface geology: cratonic lithosphere is generally thick and electrically resistive, while much thinner lithosphere is seen beneath mobile belts. In areas of relatively uniform resistivity structure, we have constructed resistivity-depth profiles and use new laboratory data to place constraints on the water content of lithospheric mantle. Uncertainty in our estimates arises from differences between different laboratory results, but our data are generally consistent with a slightly damp upper lithospheric mantle above a dry and strong cratonic root. Other areas show complexity of structure that is difficult to understand using current knowledge of conductivity -the Bushveld complex, where the mantle is highly conductive, is one such example. In southwestern Zambia, the lithosphere is seen to be very thin (around 50km) beneath mobile belt terrain, as was inferred nearly 40 years ago on the basis of high heatflow. The mantle is highly conductive, most likely due to a combination of elevated temperatures, water content and perhaps a trace amount of melting. This anomalous structure may be linked to the southwest propagation of the East African Rift system.

  20. A layer stripping approach for monitoring resistivity variations using surface magnetotelluric responses

    NASA Astrophysics Data System (ADS)

    Ogaya, Xènia; Ledo, Juanjo; Queralt, Pilar; Jones, Alan G.; Marcuello, Álex

    2016-09-01

    The resolution of surface-acquired magnetotelluric data is typically not sufficiently high enough in monitoring surveys to detect and quantify small resistivity variations produced within an anomalous structure at a given depth within the subsurface. To address this deficiency we present an approach, called "layer stripping", based on the analytical solution of the one-dimensional magnetotelluric problem to enhance the sensitivity of surface magnetotelluric responses to such subtle subsurface temporal variations in resistivity within e.g. reservoirs. Given a well-known geoelectrical baseline model of a reservoir site, the layer stripping approach aims to remove the effect of the upper, unchanging structures in order to simulate the time-varying magnetotelluric responses at depth. This methodology is suggested for monitoring all kinds of reservoirs, e.g. hydrocarbons, gas, geothermal, compress air storage, etc., but here we focus on CO2 geological storage. We study one-dimensional and three-dimensional resistivity variations in the reservoir layer and the feasibility of the method is appraised by evaluating the error of the approach and defining different detectability parameters. The geoelectrical baseline model of the Hontomín site (Spain) for CO2 geological storage in a deep saline aquifer is taken as our exemplar for studying the validity of the 1D assumption in a real scenario. We conclude that layer stripping could help detect resistivity variations and locate them in the space, showing potential to also sense unforeseen resistivity variations at all depths. The proposed approach constitutes an innovative contribution to take greater advantage of surface magnetotelluric data and to use the method as a cost-effective permanent monitoring technique in suitable geoelectrical scenarios.

  1. Use of a Fourier transform spectrometer on a balloon-borne telescope and at the multiple mirror telescope (MMT)

    NASA Technical Reports Server (NTRS)

    Traub, W. A.; Chance, K. V.; Brasunas, J. C.; Vrtilek, J. M.; Carleton, N. P.

    1982-01-01

    The design and use of an infrared Fourier transform spectrometer which has been used for observations of laboratory, stratospheric, and astronomical spectra are described. The spectrometer has a spectral resolution of 0.032/cm and has operated in the mid-infrared (12 to 13 microns) as well as the far-infrared (40 to 140 microns), using both bolometer and photoconductor cryogenic detectors. The spectrometer is optically sized to accept an f/9 beam from the multi-mirror telescope (MMT). The optical and electronic design are discussed, including remote operation of the spectrometer on a balloon-borne 102-cm telescope. The performance of the laser-controlled, screw-driven moving cat's-eye mirror is discussed. Segments of typical far-infrared balloon flight spectra, lab spectra, and mid-infrared MMT spectra are presented. Data reduction, interferogram processing, artifact removal, wavelength calibration, and intensity calibration methods are discussed. Future use of the spectrometer is outlined.

  2. Magnetotelluric inversion via reverse time migration algorithm of seismic data

    SciTech Connect

    Ha, Taeyoung . E-mail: tyha@math.snu.ac.kr; Shin, Changsoo . E-mail: css@model.snu.ac.kr

    2007-07-01

    We propose a new algorithm for two-dimensional magnetotelluric (MT) inversion. Our algorithm is an MT inversion based on the steepest descent method, borrowed from the backpropagation technique of seismic inversion or reverse time migration, introduced in the middle 1980s by Lailly and Tarantola. The steepest descent direction can be calculated efficiently by using the symmetry of numerical Green's function derived from a mixed finite element method proposed by Nedelec for Maxwell's equation, without calculating the Jacobian matrix explicitly. We construct three different objective functions by taking the logarithm of the complex apparent resistivity as introduced in the recent waveform inversion algorithm by Shin and Min. These objective functions can be naturally separated into amplitude inversion, phase inversion and simultaneous inversion. We demonstrate our algorithm by showing three inversion results for synthetic data.

  3. Report: Demographic profiles and sleep quality among patients on methadone maintenance therapy (MMT) in Malaysia.

    PubMed

    Zahari, Zalina; Siong, Lee Chee; Musa, Nurfadhlina; Mohd Yasin, Mohd Azhar; Choon, Tan Soo; Mohamad, Nasir; Ismail, Rusli

    2016-01-01

    Poor sleep quality was frequently reported by opioid dependence patients during methadone maintenance therapy (MMT). The study investigated a sample of patients on MMT to investigate the severity and prevalence of sleep problems in MMT patients. We evaluated sleep quality and disturbances of 119 Malay male patients from MMT clinics in Kelantan, Malaysia between March and July 2013 using the Pittsburgh Sleep Quality Index (PSQI)-Malay version. Patients' demographic, clinical data, past drug history and methadone treatment variables were recorded. Patients averaged 37.5 years of age (SD 6.79) and their mean age of first time illicit drug use was 19.3 years (SD 4.48). Their mean age of entering MMT was 34.7 years (SD 6.92) and the mean duration in MMT was 2.8 years (SD 2.13). The mean current daily dosage of methadone was 77.8 mg (SD 39.47) and ranged from 20 to 360 mg. The mean global PSQI score was 5.6 (SD 2.79) and 43.7% patients were identified as 'poor sleepers' (global PSQI scores >5). This study confirms the poor overall sleep quality among patients on MMT. The prevalence and severity of sleep problems in MMT patients should not be underestimated. PMID:26826835

  4. AO Capabilities at the MMT for the User

    NASA Astrophysics Data System (ADS)

    Lloyd-Hart, Michael M.

    2009-05-01

    The MMT operates a facility natural guide star (NGS) AO system. Diffraction limited imaging and medium and high resolution spectroscopy in the near IR are offered over the full isoplanatic field with the ARIES instrument.The system also offers imaging with unique sensitivity in the thermal IR from 3 to 10 microns thanks to its use of an adaptive secondary mirror. L and M band imaging is offered with Clio which has a 12x15 arcsec field of view with Nyquist sampling if the diffraction limt. Recent M band images from Clio show the planetary system around HR8799. In addition, 10 - 25 micron imaging is offered with the MIRAC camera, which may also be operated as a Bracewell nulling interferometer. In this mode, two large subapertures are defined within the pupil. Light from the two is combined so as to cancel the light from an unresolved star through destructive interference, while the environs are imaged in constructive interference. In this way, dust disks and planetary systems may be imaged with greatly improved contrast. The MMT also operates the first astronomical adaptive optics system to employ multiple laser guide stars (LGS). Its initial operational mode, ground-layer adaptive optics (GLAO), provides uniform stellar wavefront correction within the 2 arcmin diameter laser beacon constellation, routinely reducing the stellar image widths to < 0.3 arcsec in the J - K bands. An imaging camera,PISCES, is available for these bands with 2 arcmin field of view sampled at 0.1 arcsec/pixel. In addition, L and M band imaging will be available with Clio in the fall of 2009, opening up near all-sky coverage with near-diffraction limited image quality and emissivity of just 7%.

  5. A practical, low-noise coil system for magnetotellurics

    USGS Publications Warehouse

    Stanley, William D.; Tinkler, Richard D.

    1983-01-01

    Magnetotellurics is a geophysical technique which was developed by Cagnaird (1953) and Tikhonov (1950) and later refined by other scientists worldwide. The technique is a method of electromagnetic sounding of the Earth and is based upon the skin depth effect in conductive media. The electric and magnetic fields arising from natural sources are measured at the surface of the earth over broad frequency bands. An excellent review of the technique is provided in the paper by Vozoff (1972). The sources of the natural fields are found in two basic mechanisms. At frequencies above a few hertz, most of the energy arises from lightning in thunderstorm belts around the equatorial regions. This energy is propagated in a wave-guide formed by the earthionospheric cavity. Energy levels are higher at fundamental modes for this cavity, but sufficient energy exists over most of the audio range to be useful for sounding at these frequencies, in which case the technique is generally referred to as audio-magnetotellurics or AMT. At frequencies lower than audio, and in general below 1 Hz, the source of naturally occuring electromagnetic energy is found in ionospheric currents. Current systems flowing in the ionosphere generate EM waves which can be used in sounding of the earth. These fields generate a relatively complete spectrum of electromagnetic energy that extends from around 1 Hz to periods of one day. Figure 1 shows an amplitude spectrum characteristic of both the ionospheric and lightning sources, covering a frequency range from 0.0001 Hz to 1000 Hz. It can be seen that there is a minimum in signal levels that occurs at about 1 Hz, in the gap between the two sources, and that signal level increases with a decrease in frequency.

  6. Optical fabrication of the MMT adaptive secondary mirror

    NASA Astrophysics Data System (ADS)

    Martin, Hubert M.; Burge, James H.; Del Vecchio, Ciro; Dettmann, Lee R.; Miller, Stephen M.; Smith, Bryan K.; Wildi, Francois P.

    2000-07-01

    We describe the optical fabrication of the adaptive secondary mirror for the MMT. The 640 mm f/15 secondary consists of a flexible glass shell, 1.8 mm thick, whose shape is controlled by 336 electromagnetic actuators. It is designed to give diffraction-limited images at a wavelength of 1 micron. For generating and polishing, the shell was supported by attaching it to a rigid glass blocking body with a thin layer of pitch. It could then be figured and measured using techniques developed for rigid secondaries. The highly aspheric surface was polished with a 30 cm stressed lap and small passive tools, and measured using a swing-arm profilometer and a holographic test plate. The goal for fabrication was to produce diffraction-limited images in the visible, after simulated adaptive correction using only a small fraction of the typical actuator forces. This translates into a surface accuracy of less than 19 nm rms with correction forces of less than 0.05 N rms. We achieved a surface accuracy of 8 nm rms after simulated correction with forces of 0.02 N rms.

  7. MMT hypervelocity star survey. III. The complete survey

    SciTech Connect

    Brown, Warren R.; Geller, Margaret J.; Kenyon, Scott J. E-mail: mgeller@cfa.harvard.edu

    2014-05-20

    We describe our completed spectroscopic survey for unbound hypervelocity stars (HVSs) ejected from the Milky Way. Three new discoveries bring the total number of unbound late B-type stars to 21. We place new constraints on the nature of the stars and on their distances using moderate resolution MMT spectroscopy. Half of the stars are fast rotators; they are certain 2.5-4 M {sub ☉} main sequence stars at 50-120 kpc distances. Correcting for stellar lifetime, our survey implies that unbound 2.5-4 M {sub ☉} stars are ejected from the Milky Way at a rate of 1.5 × 10{sup –6} yr{sup –1}. These unbound HVSs are likely ejected continuously over the past 200 Myr and do not share a common flight time. The anisotropic spatial distribution of HVSs on the sky remains puzzling. Southern hemisphere surveys like SkyMapper will soon allow us to map the all-sky distribution of HVSs. Future proper motion measurements with Hubble Space Telescope and Gaia will provide strong constraints on origin. Existing observations are all consistent with HVS ejections from encounters with the massive black hole in the Galactic center.

  8. Magnetotelluric Study of the Southern Pamir, Tajikistan

    NASA Astrophysics Data System (ADS)

    Korolevski, W.; Ritter, O.; Weckmann, U.; Rybin, A.; Matiukov, V.

    2014-12-01

    The Pamir region at the western prolongation of the Tibet-Himalaya orogen is a high plateau which accommodated the India-Asia collision by crustal shortening and thickening. The same east-west-trending orogenic belts, corresponding to continental terranes which amalgamated with Asia prior to the collision with India, wrap around the Pamir and Tibet. The southern Pamir is equivalent to the Lhasa terrane in Tibet and consists of Paleozoic-Mesozoic meta-sedimentary rocks, rare Proterozoic gneisses, and voluminous Creaceous-Palaeogene granitoids. The Pamir, however, has been displaced northward by approximately 600km with respect to the Tarim Basin. Today, there is strong geophysical evidence that a slab of Asian lithosphere has been underthrust south-southeastward beneath the Pamir. In summer 2013 we installed 85 broad-band magnetotelluric (MT) stations in the southern Pamir covering a 200km wide and 100km long area between Murghab and Khorugh, with a site spacing of approximately 8km. MT data quality is excellent in the sparsely populated southeastern Pamir plateau and heterogeneous or even strongly disturbed by electromagnetic noise in the populated southwestern Pamir. The magnetotelluric survey was part of the interdisciplinary TIPTIMON (Tien-Shan-Pamir Monitoring Program) project. 3D inversion of the data reveals a prominent low-resistivity zone at a depth of approx. 10 km. This anomaly, with resistivities below 10 Ωm, extends across the entire southeastern Pamir and appears to be limited to the West by the Shakdara dome. The crystalline basement of the Shakdara dome is imaged as resistive material. We interpret the observed low resistivity of the southeastern Pamir is as partially molten felsic material at middle to lower crustal levels.

  9. A phenomenological and thermodynamic study of the water permeation process in corn starch/MMT films.

    PubMed

    Slavutsky, Aníbal M; Bertuzzi, María A

    2012-09-01

    Water transport in edible films of starch based products is a complex phenomenon due to the strong interaction of sorbed water molecules with the polymeric structure of starch. Moisture sorption isotherms of starch and starch/MMT films were obtained. The results indicated that nanoclay incorporation produces a decrease of water uptake at all temperatures analysed. Thermodynamic parameters showed that sorption process is less favourable when MMT is incorporated into the starch matrix. Effect of driving force and water activity (aw) values at each side of the film on permeability and diffusivity coefficients were analysed. The effect of the tortuous pathway generated by MMT incorporation was significant only in the middle and lower range of aw. At high aw range the plasticizing effect of water dominated and MMT incorporation had little effect on the water barrier properties of these films. PMID:24751076

  10. Comparison study of magnetotelluric inversion using different transfer functions

    NASA Astrophysics Data System (ADS)

    Bierman, David Frank

    Near-surface inhomogeneities (NSI) are a major problem that distorts magnetotelluric (MT) data. In this thesis, I have developed a method of 3D inversion of MT data based on the phase-tensor approach. Theoretically, unlike conventional MT apparent resistivities, the phase-tensor data are not distorted by the near-surface inhomogeneities and thus should provide more reliable information about deep geoelectrical structures. I have derived the relationships between Frechet derivatives of the phase tensor and those of the MT impedance components. Once the sensitivities are known, the method closely follows Consortium for Electromagnetic Modeling and Inversion's (CEMI's) 3D MT inversion algorithm, which is based on the integral equation (IE) formulation of EM field equations and receiver footprint approach. In this thesis, I conduct a comparison study of 3D MT inversions, using impedance tensor and phase tensor methods. I present a case study using the MT data from the McArthur River area. The results from the impedance tensor compared well with the results from other publications. The phase tensor results did not compare well with any other results. This indicates that the phase tensor method, being theoretically very robust to near-surface distortions, in practice does not work as well as one would expect. I explain this phenomenon by the significant effects of noise in the field MT data on the components of the phase tensor.

  11. 3D magnetotelluric inversion with full distortion matrix

    NASA Astrophysics Data System (ADS)

    Gribenko, A. V.; Zhdanov, M. S.

    2014-12-01

    Distortion of regional electric fields by local structures represent one of the major problems facing three-dimensional magnetotelluric (MT) interpretation. Effect of 3D local inhomogenities on MT data can be described by a real 2x2 distortion matrix. In this project we develop a method of simultaneous inversion of the full MT impedance data for 3D conductivity distribution and for the distortion matrix. Tikhonov regularization is employed to solve the resulting inverse problem. Integral equations method is used to compute MT responses. Minimization of the cost functional is achieved via conjugate gradient method. The inversion algorithm is tested on the synthetic data from Dublin Secret Model II (DSM 2) for which multiple inversion solutions are available for comparison. Inclusion of the distortion matrix provides faster convergence and allows coarser discretization of the near-surface while achievingsimilar or better data fits as inversion for the conductivity only with finely discretized shallow regions. As a field data example we chose a subset of the EarthScope MT dataset covering Great Basin and adjacent areas of the Western United States. Great Basin data inversion identified several prominent conductive zones which correlate well with areas of tectonic and geothermal activity.

  12. Magnetotelluric measurements on the Methana Peninsula (Greece): modelling and interpretation

    NASA Astrophysics Data System (ADS)

    Volti, Theodora K.

    1999-01-01

    As a first deep geophysical survey, thirteen magnetotelluric and magnetovariation soundings in the period range of 0.0085-6000 s have been carried out in the Methana Peninsula and Trizina area (Greece), which form the western part of the active Hellenic Volcanic Arc. Data have been processed using robust techniques and further analysed using decomposition methods in order to find the regional azimuth. By using the smooth inverse of Smith and Booker (J. Geophys. Res. 96, 3905-3922, 1991), the 2-D modelling has resolved a low-resistivity area (<30 Ω m) at depths of 2-3 km beneath the volcanics, whereas elsewhere the resistivity is much higher (>100 Ω m). Parkinson induction arrows also at the range 0.01-0.1 s point towards the centre of the peninsula. The conductivity anomaly is interpreted as being connected with the volcanic history of Methana, as a cooler remnant of former magmatic activity. The contrast with the much higher resistivities suggested at depths >5 km, is discussed in terms of fluid mobility, limitation of the MT method and extensional processes in the southern Aegean.

  13. Very long period magnetotellurics at Tucson observatory - Estimation of impedances

    NASA Astrophysics Data System (ADS)

    Egbert, Gary D.; Booker, John R.; Schultz, Adam

    1992-10-01

    Eleven years (1932-1942) of electric potential and magnetic measurements at the Tucson observatory represent a unique very long period magnetotelluric (MT) data set. We report here on a careful reanalysis of this data using modern processing techniques. We have developed and used novel methods of separating out the quasi-periodic daily variations fields and for cleaning up outliers and filling in missing data in the time domain. MT impedance tensors, estimated using the cleaned and filled data and using robust frequency domain methods, are well determined and smoothly varying for periods between 4 hours and 10 days. At longer periods the electric field data are swamped by large-amplitude incoherent noise, particularly after the third year of the experiment. Although we find no evidence for contamination of any field components by oceanic motional induction at tidal periods, the MT impedance do show evidence of small systematic biases due to finite spatial scale geomagnetic sources at harmonics of the daily variation period.

  14. Characterization of Clastic Dikes Using Controlled Source Audio Magnetotellurics

    NASA Astrophysics Data System (ADS)

    Persichetti, J. A.; Alumbaugh, D.

    2001-12-01

    A site consisting of 3D geology on the Hanford Reservation in Hanford, Washington, has been surveyed using Controlled Source Audio Magnetotellurics (CSAMT) to determine the method's ability to detect clastic dikes. The dikes are fine-grained, soft-sediment intrusions, formed by the buoyant rise of buried, unconsolidated, water rich mud into overlying unconsolidated sediment. The dikes are of major importance because they may act as natural barriers inhibiting the spread of contaminants, or as conduits, allowing the contaminants to be quickly wicked away from the contaminant storage tanks that may be located in close vicinity of the dikes. The field setup consisted of a 33 meter by 63 meter receiver grid with 3 meter spacing in all directions with the transmitter positioned 71.5 meters from the center of the receiver grid. A total of 12 frequencies were collected from 1.1kHz to 66.2kHz. The CSAMT data is being analyzed using a 2D CSAMT RRI code (Lu, Unsworth and Booker, 1999) and a 2D MT RRI code (Smith and Booker, 1991). Of interest is examining how well the 2D codes are able to map 3D geology, the level of resolution that is obtained, and how important it is to include the 3D source in the solution. The ultimate goal is to determine the applicability of using CSAMT for mapping these types of features at the Hanford Reservation site.

  15. Magnetotelluric investigations at Mount Hood, Oregon

    SciTech Connect

    Mozley, E.C.; Goldstein, N.E.; Morrison, H.F.

    1986-10-01

    Magnetotelluric data, with both electric and magnetic field references for noise cancellation, were collected at accessible locations around and as close as possible to the Mount Hood andesite-dacite volcano. The purpose of the study was to identify and map conductive features and to relate them to the thermal regime of the region. Several conductors could be discerned. The shallowest, at a depth of around 500 m below the surface, was identified as a flow of heated water moving away from the summit: the deepest (--50 km) might be a melt zone in the upper mantle. Of particular interest is an elongate conductor that strikes N 10/sup 0/ W and extends from a depth of 12 km down to 22 km. Because the conductor strike is close to the trend of the chain of Cascade volcanoes and because of the high conductive thermal gradients reported for the area, this feature was initially believed to be a zone of partial melt following the volcanic axis. However, because no teleseismic P wave velocity anomaly has been found, the cause of the conductor is more problematic. While the existence of small zones of melt cannot be ruled out, it is possible that the conductor is caused by a large volume of intensely deformed rocks with brine-filled microfractures.

  16. Low Power Long Period Magnetotelluric System

    NASA Astrophysics Data System (ADS)

    Narod, B. B.; Bennest, J. R.; Booker, J. R.

    2001-12-01

    We have constructed a new MT system for periods longer than 1 second that uses substantially less power and is considerably easier to deploy than predecessors, such as the Geological Survey of Canada [GSC] Long Period Intelligent Magnetotelluric System [LIMS]. Technical aspects of these new systems include: Fully watertight; light weight [5 kg w/o magnetometer head], Eurocard card cage, 1.7 watt power consumption - 140mA @ 12vdc, built-in solar panel charge controller, GPS-disciplined timekeeping accurate to 1ms, 24-bit 8 Hz Analog to Digital conversion, data storage on a PCMCIA flash disk [85M and up], magnetic field: +/- 80,000 nT range with 10pT resolution, electric field ch: +/- 200 mv with sub-microvolt useful resolution. A setup program automatically handles most deployment tasks including recording site location and data start time. Data are logged in files that begin at hour marks and are of one-hour duration. They are thus automatically synchronous at an array of instruments. Data retrieval consists of moving a PCMCIA card from the data logger to a laptop computer. A revision of this system is already in progress. It will feature PC104 card formats and will be lighter, smaller and have even lower power consumption. Ten of these systems were deployed for the first time during August and September 2001, in Argentina. Sample data from these deployments will be shown.

  17. Motional magnetotellurics by long oceanic waves

    NASA Astrophysics Data System (ADS)

    Shimizu, Hisayoshi; Utada, Hisashi

    2015-04-01

    The observation of electromagnetic signals by ocean bottom electromagnetometers in association with the Tohoku tsunami of 2011 March 11 has raised the opportunity to re-examine the physics of motional induction due to oceanic long waves in the framework of 1-D magnetotellurics (MT). Although a propagating tsunami has a complex structure, the induced electromagnetic field can be simply approximated as a plane wave (though a simple thin-sheet approximation is not valid at higher frequencies). We found that the MT impedance due to a surface gravity wave (or the `motional impedance') is influenced largely by the dispersion of the wave if the period is sufficiently short or the electrical conductivity of the seabed is low. The tipper due to the motional induction (or the `motional tipper') and motional impedance are essentially identical if the underneath structure is 1-D. It would be possible to estimate the motional impedance and tipper from the observed ocean bottom electromagnetic field at the time of passing of a tsunami. The wave amplitude must be much greater than several tens of centimetres for the motional impedance and tipper estimation to be free from the effects of external sources. However, the obtained motional impedance and tipper will mostly represent the property of the wave and use of them may not be suitable to discuss the subseafloor conductivity structure.

  18. West Flank Coso, CA FORGE Magnetotelluric Inversion

    DOE Data Explorer

    Doug Blankenship

    2016-05-16

    The Coso Magnetotelluric (MT) dataset of which the West Flank FORGE MT data is a subset, was collected by Schlumberger / WesternGeco and initially processed by the WesternGeco GeoSolutions Integrated EM Center of Excellence in Milan, Italy. The 2011 data was based on 99 soundings that were centered on the West Flank geothermal prospect. The new soundings along with previous data from 2003 and 2006 were incorporated into a 3D inversion. Full impedance tensor data were inverted in the 1-3000 Hz range. The modelling report notes several noise sources, specifically the DC powerline that is 20,000 feet west of the survey area, and may have affected data in the 0.02 to 10 Hz range. Model cell dimensions of 450 x 450 x 65 feet were used to avoid computational instability in the 3D model. The fit between calculated and observed MT values for the final model run had an RMS value of 1.807. The included figure from the WesternGeco report shows the sounding locations from the 2011, 2006 and 2003 surveys.

  19. MTpy: A Python toolbox for magnetotellurics

    NASA Astrophysics Data System (ADS)

    Krieger, Lars; Peacock, Jared R.

    2014-11-01

    We present the software package MTpy that allows handling, processing, and imaging of magnetotelluric (MT) data sets. Written in Python, the code is open source, containing sub-packages and modules for various tasks within the standard MT data processing and handling scheme. Besides the independent definition of classes and functions, MTpy provides wrappers and convenience scripts to call standard external data processing and modelling software. In its current state, modules and functions of MTpy work on raw and pre-processed MT data. However, opposite to providing a static compilation of software, we prefer to introduce MTpy as a flexible software toolbox, whose contents can be combined and utilised according to the respective needs of the user. Just as the overall functionality of a mechanical toolbox can be extended by adding new tools, MTpy is a flexible framework, which will be dynamically extended in the future. Furthermore, it can help to unify and extend existing codes and algorithms within the (academic) MT community. In this paper, we introduce the structure and concept of MTpy. Additionally, we show some examples from an everyday work-flow of MT data processing: the generation of standard EDI data files from raw electric (E-) and magnetic flux density (B-) field time series as input, the conversion into MiniSEED data format, as well as the generation of a graphical data representation in the form of a Phase Tensor pseudosection.

  20. Synthesis of CarAlg/MMt nanocomposite hydrogels and adsorption of cationic crystal violet.

    PubMed

    Mahdavinia, Gholam Reza; Aghaie, Huriyeh; Sheykhloie, Hossein; Vardini, Mohammad Taghi; Etemadi, Hossein

    2013-10-15

    CarAlg/MMt nanocomposite hydrogels composed of kappa-carrageenan (Car) and sodium alginate (Alg) biopolymers were synthesized by incorporation of sodium montmorillonite (Na-MMt) nanoclay. Acrylamide (AAm), methylenebisacrylamide (MBA), and ammonium persulfate (APS) were used as monomer, crosslinker, and initiator, respectively. The structure and morphology of nanocomposites were characterized by XRD, SEM, and TEM techniques. The XRD results showed exfoliated MMt nanoclay and exfoliation of MMt was confirmed by TEM graph. The resulting nanocomposites were evaluated to remove cationic crystal violet (CV) dye from water. According to data, the adsorption capacity of nanocomposites was enhanced as the clay content was increased. The experimental data were analyzed according to both Langmuir and Freundlich models and experimental maximum adsorption capacity was obtained 88.8 mg g(-1). By studying the effect of pH on the dye adsorption capacity of nanocomposites, it was revealed that the adsorption capacity of nanocomposites was enhanced at acidic pHs as the Na-MMt nanoclay and kappa-carrageenan components were increased. PMID:23987355

  1. WALDIM: A code for the dimensionality analysis of magnetotelluric data using the rotational invariants of the magnetotelluric tensor

    NASA Astrophysics Data System (ADS)

    Martí, A.; Queralt, P.; Ledo, J.

    2009-12-01

    In the magnetotelluric (MT) method, the analysis of geoelectric dimensionality has acquired special importance in the last years, because numerical codes have made it possible to model and invert data using either one-dimensional (1D), two-dimensional (2D) or three-dimensional (3D) approaches. We present a FORTRAN code termed WALDIM to perform the dimensionality analysis of a set of MT data, according to the WAL rotational invariants criteria. These criteria are based on the possible annulment of the invariants of the MT tensor, which allow retrieval of as much information as possible from this tensor, without taking any a priori dimensionality assumption. When determining the dimensionality of real and therefore noisy data, two problems arise. The first is due to the data errors, which propagate into the invariants values, and therefore, to the determination of the dimensionality. The second is the fact that the invariants are rarely precisely zero, and the definition of a threshold is necessary. To solve these problems, WALDIM takes into account the data errors. Additionally, the dimensionality results can be grouped into frequency bands. Thus, we provide a software utility that allows providing a robust description of the dimensionality, and the parameters necessary for data correction prior to modeling. Given its completeness at analyzing the MT tensor for both individual and bands of frequencies, this code is meant to be a practical tool for MT data analysis.

  2. Using Empirical Mode Decomposition to process Marine Magnetotelluric Data

    NASA Astrophysics Data System (ADS)

    Chen, J.; Jegen, M. D.; Heincke, B. H.; Moorkamp, M.

    2014-12-01

    The magnetotelluric (MT) data always exhibits nonstationarities due to variations of source mechanisms causing MT variations on different time and spatial scales. An additional non-stationary component is introduced through noise, which is particularly pronounced in marine MT data through motion induced noise caused by time-varying wave motion and currents. We present a new heuristic method for dealing with the non-stationarity of MT time series based on Empirical Mode Decomposition (EMD). The EMD method is used in combination with the derived instantaneous spectra to determine impedance estimates. The procedure is tested on synthetic and field MT data. In synthetic tests the reliability of impedance estimates from EMD-based method is compared to the synthetic responses of a 1D layered model. To examine how estimates are affected by noise, stochastic stationary and non-stationary noise are added on the time series. Comparisons reveal that estimates by the EMD-based method are generally more stable than those by simple Fourier analysis. Furthermore, the results are compared to those derived by a commonly used Fourier-based MT data processing software (BIRRP), which incorporates additional sophisticated robust estimations to deal with noise issues. It is revealed that the results from both methods are already comparable, even though no robust estimate procedures are implemented in the EMD approach at present stage. The processing scheme is then applied to marine MT field data. Testing is performed on short, relatively quiet segments of several data sets, as well as on long segments of data with many non-stationary noise packages. Compared to BIRRP, the new method gives comparable or better impedance estimates, furthermore, the estimates are extended to lower frequencies and less noise biased estimates with smaller error bars are obtained at high frequencies. The new processing methodology represents an important step towards deriving a better resolved Earth model to

  3. Correction of magnetotelluric static shift by analysis of 3D forward modelling and measured test data

    NASA Astrophysics Data System (ADS)

    Zhang, Kun; Wei, Wenbo; Lu, Qingtian; Wang, Huafeng; Zhang, Yawei

    2016-06-01

    To solve the problem of correction of magnetotelluric (MT) static shift, we quantise factors that influence geological environments and observation conditions and study MT static shift according to 3D MT numerical forward modelling and field tests with real data collection. We find that static shift distortions affect both the apparent resistivity and the impedance phase. The distortion results are also related to the frequency. On the basis of synthetic and real data analysis, we propose the concept of generalised static shift resistivity (GSSR) and a new method for correcting MT static shift. The approach is verified by studying 2D inversion models using synthetic and real data.

  4. Superabsorbent nanocomposite (alginate-g-PAMPS/MMT): synthesis, characterization and swelling behavior.

    PubMed

    Yadav, Mithilesh; Rhee, Kyong Yop

    2012-09-01

    A superabsorbent composite (alginate-g-PAMPS/MMT) was prepared by graft copolymerization from alginate, 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS) and Na+ montmorillonite (MMT) in an inert atmosphere. Effects of polymerization variables on water absorbency, including the content of Na+ montmorillonite, sodium alginate, N,N'-methylenebisacrylamide and AMPS, were studied. The introduced montmorillonite formed a loose and porous surface and improved the water absorbency of the alginate-g-PAMPS/MMT superabsorbent composite. Swelling behaviors of the superabsorbent composites in various cationic salt solutions (NaCl, CaCl2 and FeCl3) and anionic salt solutions (NaCl and Na2SO4) were also systematically investigated. The superabsorbent composite was further characterized using Fourier transform infrared spectroscopy (FTIR), rheology, thermogravimetric analysis (TGA), X-ray diffraction (XRD) and scanning electron microscopy (SEM) taking alginate-g-PAMPS as a reference. PMID:24751026

  5. 3-D inversion of magnetotelluric Phase Tensor

    NASA Astrophysics Data System (ADS)

    Patro, Prasanta; Uyeshima, Makoto

    2010-05-01

    Three-dimensional (3-D) inversion of the magnetotelluric (MT) has become a routine practice among the MT community due to progress of algorithms for 3-D inverse problems (e.g. Mackie and Madden, 1993; Siripunvaraporn et al., 2005). While availability of such 3-D inversion codes have increased the resolving power of the MT data and improved the interpretation, on the other hand, still the galvanic effects poses difficulties in interpretation of resistivity structure obtained from the MT data. In order to tackle the galvanic distortion of MT data, Caldwell et al., (2004) introduced the concept of phase tensor. They demonstrated how the regional phase information can be retrieved from the observed impedance tensor without any assumptions for structural dimension, where both the near surface inhomogeneity and the regional conductivity structures can be 3-D. We made an attempt to modify a 3-D inversion code (Siripunvaraporn et al., 2005) to directly invert the phase tensor elements. We present here the main modification done in the sensitivity calculation and then show a few synthetic studies and its application to the real data. The synthetic model study suggests that the prior model (m_0) setting is important in retrieving the true model. This is because estimation of correct induction scale length lacks in the phase tensor inversion process. Comparison between results from conventional impedance inversion and new phase tensor inversion suggests that, in spite of presence of the galvanic distortion (due to near surface checkerboard anomalies in our case), the new inverion algorithm retrieves the regional conductivitity structure reliably. We applied the new inversion to the real data from the Indian sub continent and compared with the results from conventional impedance inversion.

  6. Enhanced mechanical and thermal properties of CNT/HDPE nanocomposite using MMT as secondary filler

    NASA Astrophysics Data System (ADS)

    Ali Mohsin, M. E.; Arsad, Agus; Fouad, H.; Jawaid, M.; Alothman, Othman Y.

    2014-05-01

    This study explains the influence of secondary filler on the dispersion of carbon nanotube (CNT) reinforced high density polyethylene (HDPE) nanocomposites (CNT/HDPE). In order to understand the mixed-fillers system, Montmorillonite (MMT) was added to CNT/HDPE nanocomposites. It was followed by investigating their effect on the thermal, mechanical and XRD properties of the aforesaid nanocomposite. Incorporation of 3 wt% each of MMT into CNT/HDPE nanocomposite resulted to the increased values for the tensile and flexural strength, as compared to the pure HDPE matrix. The thermal analysis result showed improved thermal stability of the formulated nanocomposites.

  7. Magnetotelluric studies at the Cerro Prieto geothermal field

    SciTech Connect

    Goubau, W.M.; Goldstein, N.E.; Clarke, J.

    1981-01-01

    During three years of magnetotelluric surveying, data were acquired at 26 sites distributed over 190 km/sup 2/ around the production area. A relatively well-defined strike of N27W +- 1.5/sup 0/ (magnetic) was established. The simple model shown suggests a lateral discontinuity in the vicinity of Nueva Leon.

  8. Structure of the Tongariro Volcanic system: Insights from magnetotelluric imaging

    NASA Astrophysics Data System (ADS)

    Hill, Graham J.; Bibby, Hugh M.; Ogawa, Yasuo; Wallin, Erin L.; Bennie, Stewart L.; Caldwell, T. Grant; Keys, Harry; Bertrand, Edward A.; Heise, Wiebke

    2015-12-01

    The dynamics of magma reservoirs (the main repositories for eruptible magma) play a fundamental role in the style and behaviour of volcanic systems. A key first step in understanding these systems is to identify their location and size accurately. We present results from a broadband magnetotelluric study of the Tongariro Volcanic system and discuss how the results fit within current petrological models. The Tongariro Volcanic system is a composite andesitic cone complex, located at the southern end of the Taupo Volcanic Zone in the central North Island of New Zealand. We use data from 136 broadband magnetotelluric soundings within a 25 × 35 km area covering the volcanic system to construct a 3D image of the magmatic system of the Tongariro Volcanic Complex including Mount Ngauruhoe. The structure of the Tongariro magmatic system has been determined from 3D forward and inverse modelling of the magnetotelluric data and allowed for an estimation of the melt fraction present within the system. 3D inverse modelling of the magnetotelluric data shows: a well-developed shallow low resistivity zone outlining the geothermal system; a zone of even lower resistivity representing a shallow crustal magma accumulation zone located at a depth of ˜4-12 km offset to the east of the Tongariro vent system; and a zone with a slightly higher resistivity connecting these two components of the magmatic system providing the path for magmatic fluids from the deeper source region to reach the surface during eruptive events.

  9. Electrical conductivity of the Fennoscandian Shield margin from recent magnetotelluric profiles

    NASA Astrophysics Data System (ADS)

    Smirnov, M. Yu.; Korja, T.; Pedersen, L. B.

    2009-04-01

    central part of the TESZ in the Polish Trough at mid-crustal depths is well resolved. The upper mantle of the Precambrian Craton is more resistive than the younger Paleozoic lithosphere by at least one order of magnitude. We can summarize the results from these profiles in the following conclusions. Magnetotelluric data revealed remarkable features at the crustal level along each profile. Some of them were not clearly identified before by other geophysical methods. Conductors like alum shales are very well indicated in the final models. Electrical lithosphere is thick beneath the Fennoscandian Shield and significantly thinner beneath younger domains. The resulting models shows the conductivity contrast at a depth of about 150 km across the cratonic margin to be at least one order of magnitude.

  10. Magnetotelluric signature of anticlines in Iran's Sehqanat oil field

    NASA Astrophysics Data System (ADS)

    Mansoori, Isa; Oskooi, Behrooz; Pedersen, Laust B.

    2015-07-01

    The magnetotelluric (MT) method has proved to be an effective tool in hydrocarbon exploration especially in areas with geological structures/formations where seismic reflection provides neither good quality data nor images. The Sehqanat oil field located in the sedimentary zone of Zagros in SW of Iran is a typical example. It is covered by the high velocity and heterogeneous formation of Gachsaran, which is exposed at the surface and has a thickness varying from 500 m to more than 2 km in the region. Gachsaran is composed mainly of salt and evaporites overlying, as a cap rock, the Asmari limestone formation which is the main reservoir in all oil fields of Iran along the Zagros range. The main geological interface which is targeted to be imaged with the MT method is the contact between the highly conductive evaporites of the Gachsaran formation and the underlying more resistive carbonates of the Asmari formation. MT data at more than 600 stations along five parallel SW-NE profiles crossing the main geological trend of the study area and transient electromagnetic data over 400 stations to be used for static shift corrections of the MT data were available. Dimensionality and strike analysis of the MT data show dominant two-dimensional (2-D) conditions in almost all sites and periods. The 2-D resistivity models resolved the boundary between Gachsaran and Asmari formations as a transition zone from highly conductive to resistive structures. The Sehqanat anticline has also been delineated throughout the 2-D resistivity sections as a resistive dome-shaped body located in the middle part of the MT profiles. There is a considerable correlation between the 2-D resistivity models and the adjacent 2-D reflection seismic sections so that a more reliable interpretation on the hydrocarbon trap of the Sehqanat anticline can be obtained.

  11. Very long period magnetotellurics at Tucson Observatory: Estimation of impedances

    SciTech Connect

    Egbert, G.D.; Booker, J.R.; Schultz, A.

    1992-10-10

    Eleven years (1932-1942) of electric potential and magnetic measurements at the Tucson observatory represent a unique very long period magnetotelluric (MT) data set. The authors report on a careful reanalysis of this data using modern processing techniques. They have developed and used novel methods for separating out the quasi-periodic daily variation fields and for cleaning up outliers and filling in missing data in the time domain. MT impedance tensors, estimated using the cleaned and filled data and using robust frequency domain methods, are well determined and smoothly varying for periods between 4 hours and 10 days. At longer periods the electric field data are swamped by large-amplitude incoherent noise, particularly after the third year of the experiment. Although they find no evidence for contamination of any field components by oceanic motional induction at tidal periods, the MT impedance estimates do show evidence of small systematic biases due to finite spatial scale geomagnetic sources at harmonics of the daily variation period. These periods are thus removed from the time series and not used in further analysis. They show that the resulting impedance tensor is well modeled by a real, frequency-independent distortion of a scalar impedance, which is consistent with non-inductive distortion of the electric fields by local surface geology. To estimate the undetermined static shift of the MT impedance, the authors compare the long-period MT results to equivalent MT impedances determined from 46 years of geomagnetic data. Combining the geomagnetic and undistorted MT impedances results in scalar impedance estimates for periods 0.17 < T < 91 days of unprecedented precision. However, for periods less than one day, the phase and amplitude of this impedance, while individually consistent, are not mutually consistent with any one-dimensional conductivity distribution. 51 refs., 19 figs., 4 tabs.

  12. POLARIS Magnetotelluric Overview and Update - Spring 2004

    NASA Astrophysics Data System (ADS)

    Ferguson, I.; Samson, C.; Unsworth, M.; Asudeh, I.; Craven, J.; Atkinson, G.

    2004-05-01

    The Canadian POLARIS project includes an important component of electromagnetic studies. As part of this project, magnetotelluric (MT) equipment has been acquired to develop an infrastructure for electromagnetic soundings over depths ranging from the uppermost crust to depths of several hundreds kilometers into the asthenosphere. A key innovative feature of the POLARIS project is that MT instruments are being used in association with teleseismic techniques for imaging the Earth's structure, and for investigating seismogenic structures. MT soundings are in progress and, at the end of the project, will have been made at most of the 90 POLARIS observatory arrays on the Slave craton in the Northwest Territories, in the Casacadia region of southwestern British Columbia, and in the Precambrian Grenville Province in southern Ontario. MT equipment is also being used in studies of geomagnetically induced currents (GICs) on powerlines and pipelines. To carry out soundings at different target depths, the POLARIS MT equipment includes: audio-frequency (104 to 10 Hz) MT (AMT) systems for imaging the upper crust; broadband (102 to 10-3 Hz) MT (BBMT) systems for imaging the middle and lower crust; and long-period (1 to <10-4 Hz) MT (LMT) systems with specialized ring-core fluxgate magnetometers required for imaging at mantle depths and for geomagnetic hazard studies. More specifically, the AMT-BBMT equipment consists of six MTU-5A systems that have been procured from Phoenix Geophysics Ltd. and the LMT equipment of twenty-five ring-core NIMS systems on order from Narod Geophysics Ltd. A subset of the POLARIS MT equipment consisting of the AMT, BBMT, and fifteen of the LMT instruments is designed to be moved progressively through the POLARIS arrays providing MT responses over a broad frequency range. The remaining ten LMT instruments are to be deployed at carefully selected POLARIS sites in satellite-telemetered observatory configuration to provide ultra-deep imaging of the mantle

  13. Magnetotelluric experiment over the ROSE area

    SciTech Connect

    Filloux, J.H.

    1982-10-10

    Seafloor observations in natural electromagnetic fluctuations diffusing into the earth have been made in the vicinity of the Pacific Rise at 12/sup 0/N and 21/sup 0/N to gather information on the electrical conductivity structure of the oceanic basement near a spreading ridge. At 21/sup 0/N the close proximity of land (Baja California) introduces a noticeable distortion of the EM fields, and consequently the magnetotelluric sounding for this area must be interpreted with caution. At both locations the conductance of the upper 200 km appears exceptionally high and the conductivity rises rapidly below, reaching 1 S m/sup -1/ or more at 350 km. The statistical significance of a prominent conductivity increase near a depth of 22.5 km detected in the inverted data from 12/sup 0/N and of a less developed one at 30 km in the case of 21/sup 0/N is discussed. Records of the magnetic variations of 21/sup 0/N taken above the spreading center, compared to records from 40 and 120 km to the west, reveal a conspicuous enhancement of the high-frequency horizontal variations in a direction slightly west of magnetic north. We interpret this distinctive feature as the signature of an electric current sheet concentrated in an extremely high conductance, relatively shallow layer electrically bridging the two seafloor areas adjacent to the spreading center. An approximate calculation suggests a conductance in excess of 3000 S per meter of ridge crest in the close vicinity of the accretion center, equivalent to 1 to 8 km of molten basalt, depending on temperature (1000/sup 0/-1200/sup 0/C.) and depth (2-10 km.). This structure is consistent with seismic refraction information for the same area and with stratigraphic reconstruction of a fossil accretion center in Samail ophiolite. An interpretation in terms of a well-developed magma chamber is irresistable, although confirmation of the existence of this feature as well as improvement of its resolution by means of additional EM data would

  14. Interpretation of magnetotelluric measurements over an electrically dispersive one-dimensional earth

    SciTech Connect

    Patella, D.

    1987-01-01

    Frequency dispersion of electromagnetic parameters of earth materials has been widely documented in recent years. It is claimed that magnetotellurics (MT)may be significantly affected by dispersion. This paper studies the MT plane-wave interpretative problem for a one-dimensional earth characterized by the presence of dispersive layers. The theoretical properties of the MT field under the dispersion hypothesis, and the main features of the dispersion phenomenon are synthetically reviewed. The examination of previously published MT curve responses over some models of dispersive earth section shows that ambiguity can arise when interpreting MT data with no other source of information. Thus it maybe almost impossible to distinguish between the response of a dispersive section and an equally probable dispersion-free section. The dispersion magnetotelluric (DMT) method is proposed as a means to resolve the ambiguity. The DMT method is based on the execution, at the same site, of an MT sounding and of an always dispersion-free dc geoelectric deep sounding.

  15. Non-linearity in Bayesian 1-D magnetotelluric inversion

    NASA Astrophysics Data System (ADS)

    Guo, Rongwen; Dosso, Stan E.; Liu, Jianxin; Dettmer, Jan; Tong, Xiaozhong

    2011-05-01

    This paper applies a Bayesian approach to examine non-linearity for the 1-D magnetotelluric (MT) inverse problem. In a Bayesian formulation the posterior probability density (PPD), which combines data and prior information, is interpreted in terms of parameter estimates and uncertainties, which requires optimizing and integrating the PPD. Much work on 1-D MT inversion has been based on (approximate) linearized solutions, but more recently fully non-linear (numerical) approaches have been applied. This paper directly compares results of linearized and non-linear uncertainty estimation for 1-D MT inversion; to do so, advanced methods for both approaches are applied. In the non-linear formulation used here, numerical optimization is carried out using an adaptive-hybrid algorithm. Numerical integration applies Metropolis-Hastings sampling, rotated to a principal-component parameter space for efficient sampling of correlated parameters, and employing non-unity sampling temperatures to ensure global sampling. Since appropriate model parametrizations are generally not known a priori, both under- and overparametrized approaches are considered. For underparametrization, the Bayesian information criterion is applied to determine the number of layers consistent with the resolving power of the data. For overparametrization, prior information is included which favours simple structure in a manner similar to regularized inversion. The data variance and/or trade-off parameter regulating data and prior information are treated in several ways, including applying fixed optimal estimates (an empirical Bayesian approach) or including them as hyperparameters in the sampling (hierarchical Bayesian). The latter approach has the benefit of accounting for the uncertainty in the hyperparameters in estimating model parameter uncertainties. Non-linear and linearized inversion results are compared for synthetic test cases and for the measured COPROD1 MT data by considering marginal probability

  16. 3D Magnetotelluric characterization of the COSO GeothermalField

    SciTech Connect

    Newman, Gregory A.; Hoversten, Michael; Gasperikova, Erika; Wannamaker, Philip E.

    2005-01-01

    Knowledge of the subsurface electrical resistivity/conductivity can contribute to a better understanding of complex hydrothermal systems, typified by Coso geothermal field, through mapping the geometry (bounds and controlling structures) over existing production. Three-dimensional magnetotelluric (MT) inversion is now an emerging technology for characterizing the resistivity structures of complex geothermal systems. The method appears to hold great promise, but histories exploiting truly 3D inversion that demonstrate the advantages that can be gained by acquiring and analyzing MT data in three dimensions are still few in number. This project will address said issue, by applying 3D MT forward modeling and inversion to a MT data set acquired over the Coso geothermal field. The goal of the project is to provide the capability to image large geothermal reservoirs in a single self-consistent model. Initial analysis of the Coso MT data has been carried out using 2D MT imaging technology to construct an initial 3D resistivity model from a series of 2D resistivity images obtained using the inline electric field measurements (Zxy impedance elements) along different measurement transects. This model will be subsequently refined through a 3D inversion process. The initial 3D resistivity model clearly shows the controlling geological structures possibly influencing well production at Coso. The field data however, also show clear three dimensionality below 1 Hz, demonstrating the limitations of 2D resistivity imaging. The 3D MT predicted data arising from this starting model show good correspondence in dominant components of the impedance tensor (Zxy and Zyx) above 1Hz. Below 1 Hz there is significant differences between the field data and the 2D model data.

  17. Detection of Deep Fluid Flow in Subduction Zones with Magnetotelluric Monitoring

    NASA Astrophysics Data System (ADS)

    Ritter, O.; Araya, J.

    2014-12-01

    After the 1995 Mw 8 Antofagasta earthquake, Husen and Kissling (2001) interpreted alterations observed in the seismic velocity structure as large-scale fluid distribution changes, deep within the subduction zone. Such large scale fluid relocation would cause similar modifications of the associated deep electrical resistivity structure. In this paper, we examine feasibility to detect such changes in the deep hydraulic system with magnetotelluric monitoring. Continuous magnetotelluric (MT) data have been recorded above the subduction zone in northern Chile as part of the Integrated Plate Boundary Observatory Chile (IPOC) with an array of 9 stations since 2007. With the MT method, electrical resistivity and lateral changes of the resistivity structure are estimated from so called transfer functions (TF). If the subsurface resistivity structure is stable, these TFs vary only within their statistical significance intervals over time. Any statistically significant deviations, particularly when observed over the network of sites, must be originated from a change in the subsurface resistivity structure. We simulate the effects of such changes on the TFs using 3D forward modelling studies. The background model is based on 3D inversion of the IPOC MT stations. The results show that detectable differences in the TFs are obtained if the resistivity decreases by 5 times of its original value in the lower continental crust over the rupture zone. The implications of these results are compared with observed changes in the TFs after the 2007 Mw 7.7 Tocopilla and 2014 Mw 8.2 Pisagua earthquakes.

  18. Probabilistic 3-D time-lapse inversion of magnetotelluric data: application to an enhanced geothermal system

    NASA Astrophysics Data System (ADS)

    Rosas-Carbajal, M.; Linde, N.; Peacock, J.; Zyserman, F. I.; Kalscheuer, T.; Thiel, S.

    2015-12-01

    Surface-based monitoring of mass transfer caused by injections and extractions in deep boreholes is crucial to maximize oil, gas and geothermal production. Inductive electromagnetic methods, such as magnetotellurics, are appealing for these applications due to their large penetration depths and sensitivity to changes in fluid conductivity and fracture connectivity. In this work, we propose a 3-D Markov chain Monte Carlo inversion of time-lapse magnetotelluric data to image mass transfer following a saline fluid injection. The inversion estimates the posterior probability density function of the resulting plume, and thereby quantifies model uncertainty. To decrease computation times, we base the parametrization on a reduced Legendre moment decomposition of the plume. A synthetic test shows that our methodology is effective when the electrical resistivity structure prior to the injection is well known. The centre of mass and spread of the plume are well retrieved. We then apply our inversion strategy to an injection experiment in an enhanced geothermal system at Paralana, South Australia, and compare it to a 3-D deterministic time-lapse inversion. The latter retrieves resistivity changes that are more shallow than the actual injection interval, whereas the probabilistic inversion retrieves plumes that are located at the correct depths and oriented in a preferential north-south direction. To explain the time-lapse data, the inversion requires unrealistically large resistivity changes with respect to the base model. We suggest that this is partly explained by unaccounted subsurface heterogeneities in the base model from which time-lapse changes are inferred.

  19. Magnetotelluric Evidence of Regional Lithospheric Modification in Ordos Block, North China

    NASA Astrophysics Data System (ADS)

    Dong, H.; Wei, W.; Ye, G.; Jin, S.; Jones, A. G.

    2013-12-01

    The Ordos Block (OB), which is located in the western part of the North China Craton (NCC), is one of the oldest and most stable cratonic blocks in Asia. To study the electrical structure of Ordos block, long period magnetotelluric (MT) array data from project SINOPROBE were acquired and modeled using three-dimensional (3D) MT inversion method. For the first time a high resolution 3D resistivity model of the lithosphere is acquired in the region. The lithosphere beneath the northern part of the OB and Hetao Graben is revealed to be geo-electrically distinct from that beneath the middle and southern Ordos. Contrary to what would be expected for a stable cratonic block, compelling evidence is presented of a large scale conductive complex in the lower crust and upper mantle beneath north Ordos and Hetao Graben. The abnormally conductive structure indicates the presence of aqueous fluids and/or inter-connected sulphides, possibly resulting from an upwelling of mantle material beneath the region. Correlating well with results of seismic studies, the evidence from independent magnetotelluric data supports a regional modification and thinning of the lithosphere, which might contribute to the extension of Hetao Graben started in late Miocene to Pliocene, as well as the uplifting of the north the Ordos Block since Neogene.

  20. Using empirical mode decomposition to process marine magnetotelluric data

    NASA Astrophysics Data System (ADS)

    Chen, Jin; Heincke, Bjoern; Jegen, Marion; Moorkamp, Max

    2012-07-01

    A major step in processing magnetotelluric (MT) data is the calculation of an impedance tensor as function of frequency from recorded time-varying electromagnetic fields. Common signal processing techniques such as Fourier transform based procedures assume that the signals are stationary over the record length, which is not necessarily the case in MT, due to the possibility of sudden spatial and temporal variations in the naturally occurring source fields. In addition, noise in the recorded electric and magnetic field data may also be non-stationary. Many modern MT processing techniques can handle such non-stationarities through strategies such as windowing of the time-series. However, it is not completely clear how extreme non-stationarity may affect the resulting impedances. As a possible alternative, we examine a heuristic method called empirical mode decomposition (EMD) that is developed to handle arbitrary non-stationary time-series. EMD is a dynamic time series analysis method, in which complicated data sets can be decomposed into a finite number of simple intrinsic mode functions. In this paper, we use the EMD method on real and synthetic MT data. To determine impedance tensor estimates we first calculate instantaneous frequencies and spectra from the intrinsic mode functions and apply the impedance formula proposed by Berdichevsky to the instantaneous spectra. We first conduct synthetic tests where we compare the results from our EMD method to analytically determined apparent resistivities and phases. Next, we compare our strategy to a simple Fourier derived impedance formula and the frequently used robust processing technique bounded-influence remote reference processing (BIRRP) for different levels of stochastic noise. All results show that apparent resistivities and phases which are calculated from EMD derived impedance tensors are generally more stable than those determined from simple Fourier analysis and only slightly worse than those from the robust

  1. Magnetotelluric Investigation of the South Aegean Volcanic Arc, Greece

    NASA Astrophysics Data System (ADS)

    Kalisperi, Despina; Romano, Gerardo; Smirnov, Maxim; Kouli, Maria; Perrone, Angela; Makris, John P.; Vallianatos, Filippos

    2014-05-01

    The South Aegean Volcanic Arc (SAVA) is a chain of volcanic islands in the South Aegean resulting from the subduction of the African tectonic plate beneath the Eurasian plate. It extends from Methana, northwest, to the Island of Nisyros southeast (450 km total length). SAVA comprises a series of dormant and historically active volcanoes, with the most prominent to be Aegina, Methana, Milos, Santorini, Kolumbo, Kos and Nisyros. The aim of the ongoing research project "MagnetoTellurics in studying Geodynamics of the hEllenic ARc (MT-GEAR)" is to contribute to the investigation of the geoelectric structure of Southern Aegean, and particularly to attempt to image the Hellenic Subduction Zone. In this context, onshore magnetotelluric (MT) measurements were recently carried out on the central and eastern part of SAVA (Milos, Santorini, Nisyros and Kos Islands). Data were collected using two MT systems running simultaneously plus a remote reference station installed in Omalos plateau (Western Crete). Robust MT data analysis of the broad-band MT soundings and the resulting model of the conductivity structure of the South Aegean Volcanic Arc is presented. The research is co-funded by the European Social Fund (ESF) and National Resources under the Operational Programme 'Education and Lifelong Learning (EdLL) within the context of the Action 'Supporting Postdoctoral Researchers' in the framework of the project title "MagnetoTellurics in studying Geodynamics of the hEllenic ARc (MT-GEAR)".

  2. Response Function Estimation of Marine Magnetotelluric Data Measured at Tristan de Cunha Hot Spot

    NASA Astrophysics Data System (ADS)

    Chen, J.; Jegen, M. D.; Baba, K.; Utada, H.

    2015-12-01

    According to classical plume theory, the Tristan da Cunha hotspot is thought to have played a major role in the rifting of the South Atlantic margins and the creation of the aseismic Walvis Ridge by impinging at the base of the continental lithosphere shortly before or during the breakup of the South Atlantic margins. To understand the tectonic processes of the opening of the South Atlantic, the formation of the Walvis ridge and to understand, whether Tristan da Cunha is the cause or the consequence of the rifting, a network of 26 ocean-bottom magnetotelluric stations (OBMT) (cooperation between GEOMAR Germany and the Earthquake Research Institute at the University of Tokyo) and 24 broadband ocean-bottom seismometers was in operation during February 2012 and January 2013 within the framework of the project ISOLDE during the second phase of the SPP 1375. To complement the ocean-bottom network and the existing stations on Tristan da Cunha, one magnetotelluric land station and two land seismometers were installed on Nightingale Island. Marine magnetotelluric data is often contaminated with different levels of non-stationary noise originating from water waves, passing ships and tilt movements of the instruments. In traditional data processing, such noisy segments are removed from the time series before processing. As a consequence only a portion of data remains for response function estimation and accordingly no information about longer periods (deeper structure) remains. However, since the focus of this study is melt anomalies in the upper mantle, long period estimators of the response function are vital. To investigate which processing method yields the more reliable estimates between tens to 100 000 seconds (i.e. penetration depth from a few kilometers to approximately 600 to 800 km) for our recorded data, we applied and compared different sophisticated preprocessing and processing methods (e.g., pre-whitening, one-stage BIRRP, advanced two-stage BIRRP and

  3. Anisotropic magnetotelluric inversion using a mutual information constraint

    NASA Astrophysics Data System (ADS)

    Mandolesi, E.; Jones, A. G.

    2012-12-01

    In recent years, several authors pointed that the electrical conductivity of many subsurface structures cannot be described properly by a scalar field. With the development of field devices and techniques, data quality improved to the point that the anisotropy in conductivity of rocks (microscopic anisotropy) and tectonic structures (macroscopic anisotropy) cannot be neglected. Therefore a correct use of high quality data has to include electrical anisotropy and a correct interpretation of anisotropic data characterizes directly a non-negligible part of the subsurface. In this work we test an inversion routine that takes advantage of the classic Levenberg-Marquardt (LM) algorithm to invert magnetotelluric (MT) data generated from a bi-dimensional (2D) anisotropic domain. The LM method is routinely used in inverse problems due its performance and robustness. In non-linear inverse problems -such the MT problem- the LM method provides a spectacular compromise betwee quick and secure convergence at the price of the explicit computation and storage of the sensitivity matrix. Regularization in inverse MT problems has been used extensively, due to the necessity to constrain model space and to reduce the ill-posedness of the anisotropic MT problem, which makes MT inversions extremely challenging. In order to reduce non-uniqueness of the MT problem and to reach a model compatible with other different tomographic results from the same target region, we used a mutual information (MI) based constraint. MI is a basic quantity in information theory that can be used to define a metric between images, and it is routinely used in fields as computer vision, image registration and medical tomography, to cite some applications. We -thus- inverted for the model that best fits the anisotropic data and that is the closest -in a MI sense- to a tomographic model of the target area. The advantage of this technique is that the tomographic model of the studied region may be produced by any

  4. Toward first light for the 6.5-m MMT Telescope

    NASA Astrophysics Data System (ADS)

    West, Steve C.; Callahan, Shawn; Chaffee, Frederic H.; Davison, Warren B.; Derigne, S. T.; Fabricant, Daniel G.; Foltz, Craig B.; Hill, John M.; Nagel, Robert H.; Poyner, Anthony D.; Williams, Joseph T.

    1997-03-01

    Operated by the Multiple Mirror Telescope Observatory (MMTO), the multiple mirror telescope (MMT) is funded jointly by the Smithsonian Institution (SAO) and the University of Arizona (UA). The two organizations equally share observing time on the telescope. The MMT was dedicated in May 1979, and is located on the summit of Mt. Hopkins (at an altitude of 2.6 km), 64 km south of Tucson, Arizona, at the Smithsonian Institution's Fred Lawrence Whipple Observatory (FLWO). As a result of advances in the technology at the Steward Observatory Mirror Laboratory for the casting of large and fast borosilicate honeycomb astronomical primary mirrors, in 1987 it was decided to convert the MMT from its six 1.8 m mirror array (effective aperture of 4.5 m) to a single 6.5 m diameter primary mirror telescope. This conversion will more than double the light gathering capacity, and will by design, increase the angular field of view by a factor of 15. Because the site is already developed and the existing building and mount will be used with some modification, the conversion will be accomplished for only about $20 million. During 1995, several major technical milestones were reached: (1) the existing building was modified, (2) the major steel telescope structures were fabricated, and (3) the mirror blank was diamond wheel ground (generated). All major mechanical hardware required to affect the conversion is now nearly in hand. Once the primary mirror is polished and lab-tested on its support system, the six-mirror MMT will be taken out of service and the conversion process begun. We anticipate that a 6 - 12 month period will be required to rebuild the telescope, install its optics and achieve f/9 first light, now projected to occur in early 1998. The f/5.4 and f/15 implementation will then follow. We provide a qualitative and brief update of project progress.

  5. Preparation and photo-catalytic activities of FeOOH/ZnO/MMT composite

    NASA Astrophysics Data System (ADS)

    Zhou, Yao; Liu, Fusheng; Yu, Shitao

    2015-11-01

    Montmorillonite (MMT) was used as the carrier for synthesis of FeOOH and FeOOH/ZnO nano-material. FeOOH and FeOOH/ZnO were synthesized by the aqueous solutions of Fe(NO3)3-HNO3 and Zn(NO3)2-NaOH/Fe(NO3)3-HNO3 with the carrier of montmorillonite respectively. Transmission electron-microscopy (TEM) and X-ray diffraction (XRD) were used to study the morphology form and structure of the nano-materials. TEM was also used to demonstrate that FeOOH/ZnO can be formed with the appropriate interface. According to UV-vis absorption spectra, FeOOH/ZnO has a better response to visible light than FeOOH and ZnO, which indicates there is some coupling effect between FeOOH and ZnO. Pentachlorophenol (PCP) was used as a representative organic pollutant to evaluate the photo-catalytic efficiency of the FeOOH/ZnO and FeOOH catalysts in visible light (λ > 400 nm). The photo-catalytic efficiency of FeOOH/ZnO/MMT is better than FeOOH/MMT. According to FTIR, changes of pH and TOC, the degradation mechanism was also discussed. PCP was degraded to aromatic ketone and chloro-hydrocarbon compounds and then to H2O, CO2 and HCl.

  6. The Adaptive Optics System for the New 6.5 Meter MMT Optical/Infrared Telescope

    NASA Astrophysics Data System (ADS)

    McGuire, Patrick C.; Lloyd-Hart, Michael; Angel, J. Roger P.; Angeli, George Z.; Johnson, Robert L.; Fitz-Patrick, Bruce C.; Davison, Warren B.; Sarlot, Roland J.; Bresloff, Cyndy J.; Hughes, John M.; Miller, Steve M.; Schaller, Phillip; Wildi, Francois P.; Kenworthy, Matthew A.; Cordova, Richard M.; Rademacher, Matthew L.; Rascon, Mario H.; Langlois, Maud; Roberts, Thomas; McCarthy, Don; Burge, James H.; Rhoadarmer, Troy A.; Shelton, J. Christopher; Jacobsen, Bruce; Salinari, Piero; Brusa, Guido; Del Vecchio, Ciro; Biasi, Roberto; Gallieni, Daniele; Sandler, David G.; Barrett, Todd K.

    1999-10-01

    The Multiple Mirror Telescope (MMT) is currently being upgraded to a single 6.5 meter diameter mirror and should see first light at prime focus in September 1999. We are constructing an F/15 adaptive optics (AO) system which will be an integral part of the new MMT with first light in early 2000, removing the effect of atmospheric turbulence so that images near the diffraction limit in the near-infrared can be achieved. The deformable element of this system is a 64 cm diameter secondary mirror composed of a 1.8 mm thick thin glass shell and 336 voice coil actuators operating at 1 kHz. This is the first system that uses the secondary mirror as the correcting element, which means thermal background is minimized. We will primarily present an overview of the adaptive optics technique, followed by select results which will include the laboratory testing of the AO system components with a solid secondary, data taken with the wavefront sensor camera at prime focus of the new MMT, and tests of the secondary mirror control system.

  7. Egg white/poly (vinyl alcohol)/MMT nanocomposite hydrogels for wound dressing.

    PubMed

    Jahani-Javanmardi, Azinsadat; Sirousazar, Mohammad; Shaabani, Yasaman; Kheiri, Farshad

    2016-08-01

    Nanocomposite hydrogels on the basis of egg white and poly (vinyl alcohol) (PVA) containing 0, 5, and 10 wt.% of montmorillonite (MMT) nanoclay were prepared by a facile cyclic freezing-thawing technique and their properties investigated for wound dressing application. The morphological, structural, thermal, physical, and in vitro cytotoxic properties of the prepared nanocomposite hydrogel wound dressings (NHWDs) were experimentally studied. The NHWDs had an exfoliated morphology with a porous structure having pores sizes in the nanometric scale. It was shown that MMT acted as cross-linker in the network of NHWDs and improved their thermal stabilities. The prepared wound dressings were transparent and their equilibrium water contents and water vapor transmission rates, as two important factors of wound dressings, were very close to the properties of human skin which means that the prepared wound dressings could interact appropriately with the damaged tissues of wounds and protect them like an artificial skin during the wound healing process. The in vitro cytotoxicity assay also confirmed the non-cytotoxic nature of the prepared NHWDs. It was finally concluded that the prepared egg white/PVA/MMT nanocomposite hydrogels are promising materials to be used as novel wound dressings in wound and burn care. PMID:27193240

  8. HISTORY AND ACCOMPLISHMENTS OF THE US EPA'S SUPERFUND INNOVATIVE TECHNOLOGY EVALUATION (SITE) MONITORING AND MEASUREMENT (MMT) PROGRAM

    EPA Science Inventory

    This manuscript presents the history and evolution of the U.S. Environmental Protection Agency's (EPA) Superfund Innovative Technology Evaluation (SITE) Monitoring and Measurement Technology (MMT) Program. This includes a discussion of how the fundamental concepts of a performanc...

  9. MM&T: Bibliography on optical testing with appendix

    NASA Astrophysics Data System (ADS)

    Cornejo-Rodriguez, A.; Caulfield, H. J.; Friday, W.

    1982-02-01

    The following is a major expansion of 'Bibliography on Various Optical Testing Methods,' by Daniel Malacara, Alejandro Cornejo, and M. V. R. K. Murty which appeared in Applied Optica, 14, 1065 - 1080(1975). It is computerized to allow for easy update and correction. The last update was in September 1979. For availability information, please contact either of the authors. The present bibliography occupies 321 pages and includes the work of Cornejo, et al. as an appendix.

  10. The IRETHERM Project: How Can We Characterize Geothermal Reservoirs in Ireland using Magnetotelluric Surveying?

    NASA Astrophysics Data System (ADS)

    Delhaye, R. P.; Jones, A. G.; Rath, V.; Brown, C.; Reay, D.

    2014-12-01

    We present results from two geophysical investigations of the north of Ireland, one of a concealed sedimentary basin and the other of an area of pre- to mid-Cambrian metasedimentary material with local microseismicity in Donegal. Magnetotelluric data have been acquired over each area as part of the IRETHERM Project in order to assess potential low-enthalpy geothermal resources. In addition, airborne frequency-domain EM response data have been used to assist in the definition of near-surface electrical structure and constraint of magnetotelluric modeling. The Rathlin Basin in Northern Ireland was identified as a potential geothermal resource due both an elevated geothermal gradient (observed in two deep boreholes) and favorable hydraulic properties in thick successions of Permian and Triassic sandstones (measured from core samples). Prior seismic experiments failed to fully image the sediments beneath the overlying flood basalt. A new experiment applying the magnetotelluric method has had more success, as the MT signal is not dissipated by the crystalline overburden. MT data were acquired at 69 sites across the north-eastern portion of the onshore Rathlin Basin and on nearby Rathlin Island in order to image the thickness, depth, and lateral continuity of the target sediments. Analyses and modeling of the data have determined a resistivity model that maps the variation in thickness of the sediment fill and the truncation of the sediments against the structurally-controlling Tow Valley Fault. Further testing of the model sensitivity to variations of the thickness of the Sherwood Sandstone Group within the sediment fill has also been performed, as the overlying sediments have lower porosities and permeabilities from core sampling. Microseismicity in a metasedimentary area of northern Donegal suggests that secondary porosity distributions along fracture planes may have been augmented, leading to elevated electrical conductivity. MT data were acquired over the epicenter

  11. Two and three-dimensional magnetotelluric inversion. Technical report, December 1, 1991--May 31, 1994

    SciTech Connect

    Booker, J.R.

    1994-06-27

    Our overall goal is to develop efficient techniques for high resolution imaging of the electrical structure of the Earth`s subsurface. We have focussed on natural source techniques. Such as magnetotellurics (MT). The main accomplishment under our past DOE funding has been to implement a new algorithm to invert MT data for multi-dimensional structure which is orders of magnitude faster and more memory efficient than competing algorithms. In our most recent work, we have substantially extended the capability of our two-dimensional code: completed basic implementation of a three-dimensional code and investigated holographic techniques able to rapidly extract images without solving for material properties. The principal new goal of our proposed research is to extend our methods to the controlled source electromagnetic (CSEM) techniques used in many industrial applications.

  12. APPLICATION OF AUDIO-MAGNETOTELLURIC SURVEYS ON SAO MIGUEL ISLAND, AZORES PORTUGAL.

    USGS Publications Warehouse

    Hoover, Donald; Rodrigues Da Silva, A.; Pierce, Herbert A.; Amaral, Roberto

    1984-01-01

    Geothermal exploration and development has been under way on Sao Miguel Island, Azores since 1975. This work had been restricted to the Fogo volcano, one of three dormant silicic volcanic centers on the island. The USGS in 1982 and 1983 conducted reconnaissance natural-source audio-magnetotelluric (AMT) surveys of all three silicic centers to evaluate the potential for geothermal systems at each and to demonstrate the utility of the method in areas of difficult terrain. Results on Fogo showed a low resistivity trend extending from the present production area upslope to the caldera boundary. The upper part of this trend is the upwelling zone of a thermal plume which supplies the production area. Further exploration and drilling are now planned for this area.

  13. Constriant inversion of 2D magnetotelluric data with anisotropic conductivities

    NASA Astrophysics Data System (ADS)

    Chen, X.; Weckmann, U.

    2011-12-01

    Within the framework of the German - South African geo-scientific research initiative Inkaba yeAfrica a series of magnetotelluric (MT) field experiments were conducted along the Agulhas-Karoo Transect in South Africa. This transect crosses several continental collision zones between the Cape Fold Belt, the Namaqua Natal Mobile Belt and the Kaapvaal Craton. Along the Cape Fold Belt (CFB) profile we can identify areas (>10 km) where MT sites exhibit phases over 90°. This phenomenon usually occurs in presence of electrical anisotropy. Due to the dense site spacing we are able to observe this behaviour consistently at several sites. The anisotropy of electrical conductivity is essentially a scale effect: Even if the conductivity is isotropic on the micro scale, it will become anisotropic on a larger scale if, in the averaging volume, preferred orientation (e.g., layering or lamination) exist. Therefore, it is necessary to understand the electrical anisotropy in more details and furthermore electrical anisotropy offers new degrees of freedom, which should allow a better interpretation of data. In 2D MT case with considering of electrical anisotropy, computing of impedance tensor requires two independent electric field solutions computed for two different source polarisations. Based on the forward problem formulation and its numerical approximation we derive partial differential equations for the sensitivities of the magnetotelluric fields with respect to the elements of the conductivity tensor within the medium. For illustration a sensitivity study for a simple synthetic model is shown. We present an algorithm for the inversion of 2D magnetotelluric data with anisotropic conductivities which is a extension of the well-known NLCG minimization algorithm to anisotropic model. To constrain the structure complexity, a penalty function consists of datamisfit, standard model roughness and quadratic variation of the conductivity tensor elements is minimized. To demonstrate the

  14. A data variance technique for automated despiking of magnetotelluric data with a remote reference

    SciTech Connect

    Kappler, K.

    2011-02-15

    The magnetotelluric method employs co-located surface measurements of electric and magnetic fields to infer the local electrical structure of the earth. The frequency-dependent 'apparent resistivity' curves can be inaccurate at long periods if input data are contaminated - even when robust remote reference techniques are employed. Data despiking prior to processing can result in significantly more reliable estimates of long period apparent resistivities. This paper outlines a two-step method of automatic identification and replacement for spike-like contamination of magnetotelluric data; based on the simultaneity of natural electric and magnetic field variations at distant sites. This simultaneity is exploited both to identify windows in time when the array data are compromised, and to generate synthetic data that replace observed transient noise spikes. In the first step, windows in data time series containing spikes are identified via intersite comparison of channel 'activity' - such as the variance of differenced data within each window. In the second step, plausible data for replacement of flagged windows is calculated by Wiener filtering coincident data in clean channels. The Wiener filters - which express the time-domain relationship between various array channels - are computed using an uncontaminated segment of array training data. Examples are shown where the algorithm is applied to artificially contaminated data, and to real field data. In both cases all spikes are successfully identified. In the case of implanted artificial noise, the synthetic replacement time series are very similar to the original recording. In all cases, apparent resistivity and phase curves obtained by processing the despiked data are much improved over curves obtained from raw data.

  15. West Flank Coso FORGE Magnetotelluric 3D Data

    SciTech Connect

    Doug Blankenship

    2016-01-01

    This is the 3D version of the MT data for the West Flank FORGE area.The Coso geothermal field has had three Magnetotelluric (MT) datasets collected including surveys in 2003, 2006, and 2011. The final collection, in 2011, expanded the survey to the west and covers the West Flank of FORGE area.This most recent data set was collected by Schlumberger/WesternGeco and inverted by the WesternGeco GeoSolutions Integrated EM Center of Excellence in Milan, Italy; the 2003 and 2006 data were integrated for these inversions in the present study.

  16. Hunting for extremely metal-poor emission-line galaxies in the Sloan Digital Sky Survey: MMT and 3.5 m APO observations

    NASA Astrophysics Data System (ADS)

    Izotov, Y. I.; Thuan, T. X.; Guseva, N. G.

    2012-10-01

    We present 6.5-m MMT and 3.5 m APO spectrophotometry of 69 H ii regions in 42 low-metallicity emission-line galaxies, selected from the data release 7 of the Sloan Digital Sky Survey to have mostly [O iii]λ4959/Hβ ≲ 1 and [N ii]λ6583/Hβ ≲ 0.1. The electron temperature-sensitive emission line [O iii] λ4363 is detected in 53 H ii regions allowing a direct abundance determination. The oxygen abundance in the remaining 16 H ii regions is derived using a semi-empirical method. The oxygen abundance of the galaxies in our sample ranges from 12 + log O/H ~ 7.1 to ~7.9, with 14 H ii regions in 7 galaxies with 12 + log O/H ≤ 7.35. In 5 of the latter galaxies, the oxygen abundance is derived here for the first time. Including other known extremely metal-deficient emission-line galaxies from the literature, e.g. SBS 0335-052W, SBS 0335-052E and I Zw 18, we have compiled a sample of the 17 most metal-deficient (with 12 + log O/H ≤ 7.35) emission-line galaxies known in the local universe. There appears to be a metallicity floor at 12 + log O/H ~ 6.9, suggesting that the matter from which dwarf emission-line galaxies formed was pre-enriched to that level by e.g. Population III stars. Based on observations with the Multiple Mirror telescope (MMT) and the 3.5 m Apache Point Observatory (APO). The MMT is operated by the MMT Observatory (MMTO), a joint venture of the Smithsonian Institution and the University of Arizona. The Apache Point Observatory 3.5-m telescope is owned and operated by the Astrophysical Research Consortium.Figures 1-3 and Tables 2-8 are available in electronic form at http://www.aanda.org

  17. Probabilistic 3-D time-lapse inversion of magnetotelluric data: Application to an enhanced geothermal system

    USGS Publications Warehouse

    Rosas-Carbajal, Marina; Linde, Nicolas; Peacock, Jared R.; Zyserman, F. I.; Kalscheuer, Thomas; Thiel, Stephan

    2015-01-01

    Surface-based monitoring of mass transfer caused by injections and extractions in deep boreholes is crucial to maximize oil, gas and geothermal production. Inductive electromagnetic methods, such as magnetotellurics, are appealing for these applications due to their large penetration depths and sensitivity to changes in fluid conductivity and fracture connectivity. In this work, we propose a 3-D Markov chain Monte Carlo inversion of time-lapse magnetotelluric data to image mass transfer following a saline fluid injection. The inversion estimates the posterior probability density function of the resulting plume, and thereby quantifies model uncertainty. To decrease computation times, we base the parametrization on a reduced Legendre moment decomposition of the plume. A synthetic test shows that our methodology is effective when the electrical resistivity structure prior to the injection is well known. The centre of mass and spread of the plume are well retrieved.We then apply our inversion strategy to an injection experiment in an enhanced geothermal system at Paralana, South Australia, and compare it to a 3-D deterministic time-lapse inversion. The latter retrieves resistivity changes that are more shallow than the actual injection interval, whereas the probabilistic inversion retrieves plumes that are located at the correct depths and oriented in a preferential north-south direction. To explain the time-lapse data, the inversion requires unrealistically large resistivity changes with respect to the base model. We suggest that this is partly explained by unaccounted subsurface heterogeneities in the base model from which time-lapse changes are inferred.

  18. Electric lithosphere-astenosphere boundary in the north-west Fennoscandia as revealed from magnetotelluric data (MaSca project)

    NASA Astrophysics Data System (ADS)

    Cherevatova, M.; Smirnov, M.

    2014-12-01

    Magnetotelluric images of the electric lithosphere-astenosphere boundary (LAB) below the north-western Fennoscandian Shield show that thickest lithosphere is in the Proterozoic Domain, not in Archaean. The Magnetotelluric (MT) method is well suited to map the depth to the LAB. The electric lithosphere is defined as the resistive outer shell overlying a highly conducting zone (astenosphere) in the upper mantle. A few extensive field campaigns have been undertaken in the Summers of 2011 to 2014 within the framework of the project "Magnetotellurics in the Scandes". The MaSca survey crosses two important boundaries: (i) the transition zone from the stable Precambrian cratonic interior to passive continental margin beneath the Caledonian orogen and the Scandinavian Mountains in western Fennoscandia; (ii) the boundary between the Archaean and Proterozoic crust and upper mantle. In this study we present the electrical resistivity models obtained from 279 MT sites (70 long-period stations among them) acquired from 2011 to 2013. We also used other sources of data available in the study area: the IMAGE observatory data, the BEAR array and two small arrays of Finnish Geological Survey (GTK). We present the results of 2D lithospheric-scale inversions obtained along four selected profiles: three profiles are NW-SE directed, thought to be perpendicular to estimated regional strike and one profile crosses the Archaean-Proterozoic boundary, thus NE-SW directed. The final interpretation models revealed thickest lithosphere is in the Palaeoproterozoic Svecofennian province and reaches depth of 300 km. The Archaean lithosphere is thinner, with depth of 200 km to 250 km.

  19. Inversion of magnetotelluric data in a sparse model domain

    NASA Astrophysics Data System (ADS)

    Nittinger, Christian G.; Becken, Michael

    2016-06-01

    The inversion of magnetotelluric data into subsurface electrical conductivity poses an ill-posed problem. Smoothing constraints are widely employed to estimate a regularized solution. Here, we present an alternative inversion scheme that estimates a sparse representation of the model in a wavelet basis. The objective of the inversion is to determine the few non-zero wavelet coefficients which are required to fit the data. This approach falls into the class of sparsity constrained inversion schemes and minimizes the combination of the data misfit in a least squares ℓ2 sense and of a model coefficient norm in a ℓ1 sense (ℓ2-ℓ1 minimization). The ℓ1 coefficient norm renders the solution sparse in a suitable representation such as the multi-resolution wavelet basis, but does not impose explicit structural penalties on the model as it is the case for ℓ2 regularization. The presented numerical algorithm solves the mixed ℓ2-ℓ1 norm minimization problem for the non-linear magnetotelluric inverse problem. We demonstrate the feasibility of our algorithm on synthetic 2-D MT data as well as on a real data example. We found that sparse models can be estimated by inversion and that the spatial distribution of non-vanishing coefficients indicates regions in the model which are resolved.

  20. Inversion of magnetotelluric data in a sparse model domain

    NASA Astrophysics Data System (ADS)

    Nittinger, Christian G.; Becken, Michael

    2016-08-01

    The inversion of magnetotelluric data into subsurface electrical conductivity poses an ill-posed problem. Smoothing constraints are widely employed to estimate a regularized solution. Here, we present an alternative inversion scheme that estimates a sparse representation of the model in a wavelet basis. The objective of the inversion is to determine the few non-zero wavelet coefficients which are required to fit the data. This approach falls into the class of sparsity constrained inversion schemes and minimizes the combination of the data misfit in a least-squares ℓ2 sense and of a model coefficient norm in an ℓ1 sense (ℓ2-ℓ1 minimization). The ℓ1 coefficient norm renders the solution sparse in a suitable representation such as the multiresolution wavelet basis, but does not impose explicit structural penalties on the model as it is the case for ℓ2 regularization. The presented numerical algorithm solves the mixed ℓ2-ℓ1 norm minimization problem for the nonlinear magnetotelluric inverse problem. We demonstrate the feasibility of our algorithm on synthetic 2-D MT data as well as on a real data example. We found that sparse models can be estimated by inversion and that the spatial distribution of non-vanishing coefficients indicates regions in the model which are resolved.

  1. Magnetotelluric Data, Central Yucca Flat, Nevada Test Site, Nevada

    SciTech Connect

    J.M. Williams; B.D. Rodriguez, and T.H. Asch

    2005-11-23

    Nuclear weapons are integral to the defense of the United States. The U.S. Department of Energy, as the steward of these devices, must continue to gauge the efficacy of the individual weapons. This could be accomplished by occasional testing at the Nevada Test Site (NTS) in Nevada, northwest of Las Vegas. Yucca Flat Basin is one of the testing areas at the NTS. One issue of concern is the nature of the somewhat poorly constrained pre-Tertiary geology and its effects on ground-water flow in the area subsequent to a nuclear test. Ground-water modelers would like to know more about the hydrostratigraphy and geologic structure to support a hydrostratigraphic framework model that is under development for the Yucca Flat Corrective Action Unit (CAU). During 2003, the U.S. Geological Survey (USGS) collected and processed Magnetotelluric (MT) and Audio-magnetotelluric (AMT) data at the Nevada Test Site in and near Yucca Flat to help characterize this pre-Tertiary geology. That work will help to define the character, thickness, and lateral extent of pre-Tertiary confining units. In particular, a major goal has been to define the upper clastic confining unit (UCCU) in the Yucca Flat area. Interpretation will include a three-dimensional (3-D) character analysis and two-dimensional (2-D) resistivity model. The purpose of this report is to release the MT sounding data for Central Yucca Flat, Profile 1, as shown in figure 1. No interpretation of the data is included here.

  2. Magnetotelluric Data, Northern Frenchman Flat, Nevada Test Site Nevada

    SciTech Connect

    J.M. Williams; B.D. Rodriguez, and T. H. Asch

    2005-11-23

    Nuclear weapons are integral to the defense of the United States. The U.S. Department of Energy, as the steward of these devices, must continue to gauge the efficacy of the individual weapons. This could be accomplished by occasional testing at the Nevada Test Site (NTS) in Nevada, northwest of Las Vegas. Yucca Flat Basin is one of the testing areas at the NTS. One issue of concern is the nature of the somewhat poorly constrained pre-Tertiary geology and its effects on ground-water flow in the area subsequent to a nuclear test. Ground-water modelers would like to know more about the hydrostratigraphy and geologic structure to support a hydrostratigraphic framework model that is under development for the Yucca Flat Corrective Action Unit (CAU). During 2003, the U.S. Geological Survey (USGS) collected and processed Magnetotelluric (MT) and Audio-magnetotelluric (AMT) data at the Nevada Test Site in and near Yucca Flat to help characterize this pre-Tertiary geology. That work will help to define the character, thickness, and lateral extent of pre-Tertiary confining units. In particular, a major goal has been to define the upper clastic confining unit (UCCU) in the Yucca Flat area. Interpretation will include a three-dimensional (3-D) character analysis and two-dimensional (2-D) resistivity model. The purpose of this report is to release the MT sounding data for Frenchman Flat Profile 3, as shown in Figure 1. No interpretation of the data is included here.

  3. Magnetotelluric Data, Southern Yucca Flat, Nevada Test Site, Nevada

    SciTech Connect

    J.M. Williams; B.D. Rodriguez, and T.H. Asch

    2005-11-23

    Nuclear weapons are integral to the defense of the United States. The U.S. Department of Energy, as the steward of these devices, must continue to gauge the efficacy of the individual weapons. This could be accomplished by occasional testing at the Nevada Test Site (NTS) in Nevada, northwest of Las Vegas. Yucca Flat Basin is one of the testing areas at the NTS. One issue of concern is the nature of the somewhat poorly constrained pre-Tertiary geology and its effects on ground-water flow in the area subsequent to a nuclear test. Ground-water modelers would like to know more about the hydrostratigraphy and geologic structure to support a hydrostratigraphic framework model that is under development for the Yucca Flat Corrective Action Unit (CAU). During 2003, the U.S. Geological Survey (USGS) collected and processed Magnetotelluric (MT) and Audio-magnetotelluric (AMT) data at the Nevada Test Site in and near Yucca Flat to help characterize this pre-Tertiary geology. That work will help to define the character, thickness, and lateral extent of pre-Tertiary confining units. In particular, a major goal has been to define the upper clastic confining unit (UCCU) in the Yucca Flat area. Interpretation will include a three-dimensional (3-D) character analysis and two-dimensional (2-D) resistivity model. The purpose of this report is to release the MT sounding data for Southern Yucca Flat, Profile 4, as shown in Figure 1. No interpretation of the data is included here.

  4. Bayesian analysis of resolved stellar spectra: application to MMT/Hectochelle observations of the Draco dwarf spheroidal

    NASA Astrophysics Data System (ADS)

    Walker, Matthew G.; Olszewski, Edward W.; Mateo, Mario

    2015-04-01

    We introduce a Bayesian method for fitting faint, resolved stellar spectra in order to obtain simultaneous estimates of redshift and stellar-atmospheric parameters. We apply the method to thousands of spectra - covering 5160-5280 Å at resolution R˜ 20 000 - that we have acquired with the MMT/Hectochelle fibre spectrograph for red giant and horizontal branch candidates along the line of sight to the Milky Way's dwarf spheroidal satellite in Draco. The observed stars subtend an area of ˜4 deg2, extending ˜3 times beyond Draco's nominal `tidal' radius. For each spectrum, we tabulate the first four moments - central value, variance, skewness and kurtosis - of posterior probability distribution functions representing estimates of the following physical parameters: line-of-sight velocity (vlos), effective temperature (Teff), surface gravity (log g) and metallicity ([Fe/H]). After rejecting low-quality measurements, we retain a new sample consisting of 2813 independent observations of 1565 unique stars, including 1879 observations for 631 stars with (as many as 13) repeat observations. Parameter estimates have median random errors of σ _{v_{los}} = 0.88 km s-1, σ _{T_{eff}} = 162 K, σlog g = 0.37 dex and σ[Fe/H] = 0.20 dex. Our estimates of physical parameters distinguish ˜470 likely Draco members from interlopers in the Galactic foreground.

  5. Factors predicting retention in treatment: 10-year experience of a methadone maintenance treatment (MMT) clinic in Israel.

    PubMed

    Peles, Einat; Schreiber, Shaul; Adelson, Miriam

    2006-05-20

    The aims were to identify predictors of treatment retention in an Israeli methadone maintenance treatment (MMT) clinic, and to compare the findings to other international settings. We prospectively studied 492 patients admitted since 1993 through 10 years to an Israeli MMT clinic associated with a university-affiliated tertiary care medical center. Analyses (Kaplan Meier and Cox regression) included methadone dose and urinalysis results (for methadone, cocaine, opiates, benzodiazepines, THC, amphetamines) of each patient in the first month and after 1 year in treatment (or during the last month if the stay was >3 months and <1 year) and patients' characteristics (modified ASI). The 1-year retention rate was 74.4%; 65.8% stopped opiate abuse after 1 year in treatment. On admission, 13.6% of patients had used cocaine: there was a net decrease of 61.6% after 1 year. Factors predicting prolonged retention in MMT treatment (Cox regression) were daily methadone dose of 100mg or greater, negative urine for opiates after 1 year, and being a parent on admission. We conclude that our good outcome results (high rate of retention after 1 year (74.4%), high proportion of opiate abuse cessation (65.8%), and net reduction in cocaine abuse, similar to normal standards in other MMT clinics elsewhere in the world, justify the expansion of the MMT clinic network in Israel in order to make treatment available to all those who need it. A protocol favoring higher methadone dosage as appropriate is recommended. PMID:16219428

  6. Scientific goals for the MMT's multi-laser-guided adaptive optics

    NASA Astrophysics Data System (ADS)

    Lloyd-Hart, Michael; Stalcup, Thomas; Baranec, Christoph; Milton, N. Mark; Rademacher, Matthew; Snyder, Miguel; Meyer, Michael; Eisenstein, Daniel

    2006-06-01

    The MMT's five Rayleigh laser guide star system has successfully demonstrated open loop wavefront sensing for both ground-layer and laser tomography adaptive optics (AO). Closed loop correction is expected for the first time in the autumn of 2006. The program is moving into its second phase: construction of a permanent facility to feed AO instruments now used with the telescope's existing natural star AO system. The new facility will preserve the thermal cleanliness afforded by the system's adaptive secondary mirror. With the present laser power of 4 W in each of the Rayleigh beacons, we will first offer ground-layer correction over a 2 arcmin field in J, H, and K bands, with expected image quality routinely 0.2 arcsec or better. Later, we will also offer imaging and spectroscopy from 1.5 to 4.8 μm with a tomographically corrected diffraction limited beam. The development of these techniques will lead to a facility all-sky capability at the MMT for both ground-layer and diffraction-limited imaging, and will be a critical advance in the tools necessary for extremely large telescopes of the future, particularly the Giant Magellan Telescope. We describe the present state of system development, planned progress to completion, and highlight the early scientific applications.

  7. Multistation magnetotellurics. Final report, 1 January 1996--30 June 1997

    SciTech Connect

    Egbert, G.D.

    1997-12-31

    The author has developed the foundations of a practical multivariate approach to processing magnetotelluric array data. Compared to current standards for magnetotelluric data processing, the multivariate approach is unique in that all available data channels are used simultaneously. The approach is outlined in this report. Using Multmtrn, a program for multiple station analysis of magnetotelluric data, the author achieved significant improvements in apparent resistivity and phase estimates in initial tests. Examples of the use of this approach are given including: Carrizo Plain and Parkfield electromagnetic profiling data; sea floor magnetotelluric (MT) data from the Gulf of Mexico; MT survey in a culturally noisy area of Bavaria; and Parkfield/Hollister earthquake monitoring array data. Experience with these projects has resulted in an improved program. The new version of the code is available at http://www.cg.NRCan.gc.ca/mtnet/mtnet.html or by contacting egbert{at}oce.orst.edu. Appendices of this report present documentation for Multmtrn.

  8. Implementation and on-sky results of an optimal wavefront controller for the MMT NGS adaptive optics system

    NASA Astrophysics Data System (ADS)

    Powell, Keith B.; Vaitheeswaran, Vidhya

    2010-07-01

    The MMT observatory has recently implemented and tested an optimal wavefront controller for the NGS adaptive optics system. Open loop atmospheric data collected at the telescope is used as the input to a MATLAB based analytical model. The model uses nonlinear constrained minimization to determine controller gains and optimize the system performance. The real-time controller performing the adaptive optics close loop operation is implemented on a dedicated high performance PC based quad core server. The controller algorithm is written in C and uses the GNU scientific library for linear algebra. Tests at the MMT confirmed the optimal controller significantly reduced the residual RMS wavefront compared with the previous controller. Significant reductions in image FWHM and increased peak intensities were obtained in J, H and K-bands. The optimal PID controller is now operating as the baseline wavefront controller for the MMT NGS-AO system.

  9. Two and three dimensional magnetotelluric inversion

    SciTech Connect

    Booker, J.

    1993-01-01

    Electrical conductivity depends on properties such as the presence of ionic fluids in interconnected pores that are difficult to sense with other remote sensing techniques. Thus improved imaging of underground electrical structure has wide practical importance in exploring for groundwater, mineral and geothermal resources, and in assessing the diffusion of fluids in oil fields and waste sites. Because the electromagnetic inverse problem is fundamentally multi-dimensional, most imaging algorithms saturate available computer power long before they can deal with the complete data set. We have developed an algorithm to directly invert large multi-dimensional data sets that is orders of magnitude faster than competing methods. We have proven that a two-dimensional (2D) version of the algorithm is highly effective for real data and have made substantial progress towards a three-dimensional (3D) version. We are proposing to cure identified shortcomings and substantially expand the utility of the existing 2D program, overcome identified difficulties with extending our method to three-dimensions (3D) and embark on an investigation of related EM imaging techniques which may have the potential for even further increasing resolution.

  10. Audio-magnetotelluric methods in reconnaissance geothermal exploration

    USGS Publications Warehouse

    Hoover, D.B.; Long, C.L.

    1976-01-01

    and 18 600 Hz where artificial VLF sources are available. As a reconnaissance technique we use AMT surveys in conjunction with regional gravity, magnetic, and telluric surveys. The exploration depth is a function of the resistivities of the lithologic section, but typically ranges from the surface to 0.2 km in low-resistivity areas and to greater than 2 km in high-resistivity regions. Results of the initial reconnaissance AMT surveys provide a rational basis for deciding on the extent of costlier follow-up surveys. As part of the U.S. Geological Survey geothermal program, surveys were conducted in Long Valley and Surprise Valley, California; the Vale, Ore-Weiser, Idaho region; and Bruneau-Grand View, Raft River, and Island Park regions of Idaho. AMT surveys in five additional known geothermal resource areas (KGRA's) have been scheduled for completion by May 1975. In the Raft River and Bruneau-Grand View regions and Long Valley, follow-up electrical surveys substantiated the effectiveness of the AMT technique for reconnaissance surveying.

  11. Canonical decomposition of magnetotelluric responses: Experiment on 1D anisotropic structures

    NASA Astrophysics Data System (ADS)

    Guo, Ze-qiu; Wei, Wen-bo; Ye, Gao-feng; Jin, Sheng; Jing, Jian-en

    2015-08-01

    Horizontal electrical heterogeneity of subsurface earth is mostly originated from structural complexity and electrical anisotropy, and local near-surface electrical heterogeneity will severely distort regional electromagnetic responses. Conventional distortion analyses for magnetotelluric soundings are primarily physical decomposition methods with respect to isotropic models, which mostly presume that the geoelectric distribution of geological structures is of local and regional patterns represented by 3D/2D models. Due to the widespread anisotropy of earth media, the confusion between 1D anisotropic responses and 2D isotropic responses, and the defects of physical decomposition methods, we propose to conduct modeling experiments with canonical decomposition in terms of 1D layered anisotropic models, and the method is one of the mathematical decomposition methods based on eigenstate analyses differentiated from distortion analyses, which can be used to recover electrical information such as strike directions, and maximum and minimum conductivity. We tested this method with numerical simulation experiments on several 1D synthetic models, which turned out that canonical decomposition is quite effective to reveal geological anisotropic information. Finally, for the background of anisotropy from previous study by geological and seismological methods, canonical decomposition is applied to real data acquired in North China Craton for 1D anisotropy analyses, and the result shows that, with effective modeling and cautious interpretation, canonical decomposition could be another good method to detect anisotropy of geological media.

  12. Multi-site magnetotelluric measurement system with real-time data analysis. Final technical report No. 210

    SciTech Connect

    Becker, J.D.; Bostick, F.X. Jr.; Smith, H.W.

    1981-09-01

    A magnetotelluric measurement system has been designed to provide a more cost effective electrical method for geothermal and mineral exploration. The theoretical requirements and sensitivities of the magnetotelluric inversion process were specifically addressed in determining system performance requirements. Significantly reduced instrument noise levels provide improved data quality, and simultaneous measurement at up to six locations provides reduced cost per site. Remotely located, battery powered, instrumentation packages return data to a central controlling site through a 2560 baud wire-line or radio link. Each remote package contains preamplifiers, data conditioning filters, and a 12-bit gain ranging A-D converter for frequencies from 0.001 Hz to 8 Hz. Data frequencies above 8 Hz are processed sequentially by a heterodyne receiver to reduce bandwidth to within the limits of the 2560 baud data link. The central data collection site provides overall control for the entire system. The system operator interacts with the system through a CRT terminal, and he receives hard copy from a matrix graphics printer. Data from the remote packages may be recorded in time sequence on a magnetic tape cartridge system, or an optional Hewlett-Packard 21MX minicomputer can be used to perform real-time frequency analysis. The results of this analysis provide feedback to the operator for improved evaluation of system performance and for selection of future measurement sites.

  13. A magnetotelluric model of the Mana Pools basin, northern Zimbabwe

    NASA Astrophysics Data System (ADS)

    Bailey, D.; Whaler, K. A.; Zengeni, T.; Jones, P. C.; Gwavava, O.

    2000-05-01

    The Mana Pools sedimentary basin lies within the Zambezi mobile belt in northern Zimbabwe. New and preexisting magnetotelluric data and the available seismic reflection data are used to constrain the basin structure and the depth to the electrical basement. Long-period magnetotelluric (LMT) data were collected at five stations along a 60 km north-south profile across the Mana Pools basin and onto the southern escarpment. These data augment an existing audiofrequency (AMT) data set from 11 sites in the same area. The subsurface apparent resistivities measured at periods sampling the basin are very low (a few Ωm). After processing both data sets, the estimated impedance tensor is decomposed, showing that the resistivity structure of the Mana Pools basin can be modeled two dimensionally. The ρ+ algorithm is used to show that there is no systematic offset in magnitude between the AMT and LMT data sets before they are combined. Minimum structure resistivity models of the Mana Pools basin compare well with the information from reflection seismic data and support its previous description as a half graben basin of ˜7 km depth. The excellent conductor in the Mana Pools basin is quite different to those seen elsewhere in the orogenic belt in that it is a feature of the sedimentary fill rather than the basement. The resistivity of the basement is low but no localized good conductor is observed; these low resistivities may result from a high degree of either chemical or tectonic alteration to the underlying rocks due to metamorphic processes and tectonic disruption during rift formation.

  14. Crustal structure beneath southern Norway imaged by magnetotellurics

    NASA Astrophysics Data System (ADS)

    Cherevatova, M.; Smirnov, M.; Korja, T.; Kaikkonen, P.; Pedersen, L. B.; Hübert, J.; Kamm, J.; Kalscheuer, T.

    2014-07-01

    We use data from two magnetotelluric profiles, ToSca10 and ToSca'09, over the Scandinavian Mountains to study the crustal structure in southern Norway. The profiles cross the major tectonic structures of the Caledonian orogen as well as the western margin of the Precambrian Baltica. Dimensionality and strike analyses indicate generally 3-D behavior of the data. However, the majority of the used data distinguishes a preferable strike direction, which is supported by the geology of the region. Hence, we employ 2-D inversion and choose to invert the determinant of the impedance tensor to mitigate 3-D effects in the data on our 2-D models. Magnetotelluric data from both profiles are inverted using a damped least squares solution based on a singular value decomposition. We improved the solution by defining the inverse model covariance matrix through gradient or Laplacian smoothing operators. The two-dimensional inversion models of the ToSca'09 and ToSca'10 field data from southern Norway derived from the damped least squares scheme with the Laplacian inverse model covariance matrix are presented. Resistive rocks, extending to the surface, image the autochthonous Southwest Scandinavian Domain and the allochthonous Western Gneiss Region. Near-surface conductors, which are located between the resistive Caledonian nappes and Precambrian basement, delineate highly conductive shallow-sea sediments, so called alum shales. They exhibit a decollement along which the Caledonian nappes were overthrust. A deeper, upper to mid-crustal conducting layer in the Southwest Scandinavian Domain may depict the remnants of closed ocean basins formed during the accretions and collisions of various Sveconorwegian terranes. In ToSca'10, the Caledonian nappes, the conducting alum shales and the deeper conductor are terminated in the west by the Faltungsgraben shear complex which represents a crustal scale boundary between the Western Gneiss Region in the west and the Southwest Scandinavian

  15. Magnetotelluric Data, North Central Yucca Flat, Nevada Test Site, Nevada

    SciTech Connect

    J.M. Williams; B.D. Rodriguez, and T.H. Asch

    2005-11-23

    Nuclear weapons are integral to the defense of the United States. The U.S. Department of Energy, as the steward of these devices, must continue to gauge the efficacy of the individual weapons. This could be accomplished by occasional testing at the Nevada Test Site (NTS) in Nevada, northwest of Las Vegas. Yucca Flat Basin is one of the testing areas at the NTS. One issue of concern is the nature of the somewhat poorly constrained pre-Tertiary geology and its effects on ground-water flow in the area subsequent to a nuclear test. Ground-water modelers would like to know more about the hydrostratigraphy and geologic structure to support a hydrostratigraphic framework model that is under development for the Yucca Flat Corrective Action Unit (CAU). During 2003, the U.S. Geological Survey (USGS) collected and processed Magnetotelluric (MT) and Audio-magnetotelluric (AMT) data at the Nevada Test Site in and near Yucca Flat to help characterize this pre-Tertiary geology. That work will help to define the character, thickness, and lateral extent of pre-Tertiary confining units. In particular, a major goal has been to define the upper clastic confining unit (UCCU) in the Yucca Flat area. Interpretation will include a three-dimensional (3-D) character analysis and two-dimensional (2-D) resistivity model. The purpose of this report is to release the MT sounding data for north central Yucca Flat, Profile 7, as shown in Figure 1. No interpretation of the data is included here.

  16. Magnetotelluric Data, Northern Yucca Flat, Nevada Test Site, Nevada

    SciTech Connect

    J.M. Williams; B.D. Rodriguez, and T.H. Asch

    2005-11-23

    Nuclear weapons are integral to the defense of the United States. The U.S. Department of Energy, as the steward of these devices, must continue to gauge the efficacy of the individual weapons. This could be accomplished by occasional testing at the Nevada Test Site (NTS) in Nevada, northwest of Las Vegas. Yucca Flat Basin is one of the testing areas at the NTS. One issue of concern is the nature of the somewhat poorly constrained pre-Tertiary geology and its effects on ground-water flow in the area subsequent to a nuclear test. Ground-water modelers would like to know more about the hydrostratigraphy and geologic structure to support a hydrostratigraphic framework model that is under development for the Yucca Flat Corrective Action Unit (CAU). During 2003, the U.S. Geological Survey (USGS) collected and processed Magnetotelluric (MT) and Audio-magnetotelluric (AMT) data at the Nevada Test Site in and near Yucca Flat to help characterize this pre-Tertiary geology. That work will help to define the character, thickness, and lateral extent of pre-Tertiary confining units. In particular, a major goal has been to define the upper clastic confining unit (UCCU) in the Yucca Flat area. Interpretation will include a three-dimensional (3-D) character analysis and two-dimensional (2-D) resistivity model. The purpose of this report is to release the MT sounding data for Profile 2, (fig. 1), located in the northern Yucca Flat area. No interpretation of the data is included here.

  17. Magnetotelluric Data, Across Quartzite Ridge, Nevada Test Site, Nevada

    SciTech Connect

    J.M. Williams; B.D. Rodriguez, and T.H. Asch

    2005-11-23

    Nuclear weapons are integral to the defense of the United States. The U.S. Department of Energy, as the steward of these devices, must continue to gauge the efficacy of the individual weapons. This could be accomplished by occasional testing at the Nevada Test Site (NTS) in Nevada, northwest of Las Vegas. Yucca Flat Basin is one of the testing areas at the NTS. One issue of concern is the nature of the somewhat poorly constrained pre-Tertiary geology and its effects on ground-water flow in the area subsequent to a nuclear test. Ground-water modelers would like to know more about the hydrostratigraphy and geologic structure to support a hydrostratigraphic framework model that is under development for the Yucca Flat Corrective Action Unit (CAU). During 2003, the U.S. Geological Survey (USGS) collected and processed Magnetotelluric (MT) and Audio-magnetotelluric (AMT) data at the Nevada Test Site in and near Yucca Flat to help characterize this pre-Tertiary geology. That work will help to define the character, thickness, and lateral extent of pre-Tertiary confining units. In particular, a major goal has been to define the upper clastic confining unit (UCCU) in the Yucca Flat area. Interpretation will include a three-dimensional (3-D) character analysis and two-dimensional (2-D) resistivity model. The purpose of this report is to release the MT soundings across Quartzite Ridge, Profiles 5, 6a, and 6b, as shown in Figure 1. No interpretation of the data is included here.

  18. Magnetotelluric array data analysis from north-west Fennoscandia

    NASA Astrophysics Data System (ADS)

    Cherevatova, M.; Smirnov, M. Yu.; Jones, A. G.; Pedersen, L. B.; Becken, M.; Biolik, M.; Cherevatova, M.; Ebbing, J.; Gradmann, S.; Gurk, M.; Hübert, J.; Jones, A. G.; Junge, A.; Kamm, J.; Korja, T.; Lahti, I.; Löwer, A.; Nittinger, C.; Pedersen, L. B.; Savvaidis, A.; Smirnov, M.

    2015-06-01

    New magnetotelluric (MT) data in north-west Fennoscandia were acquired within the framework of the project "Magnetotellurics in the Scandes" (MaSca). The project focuses on the investigation of the crustal and upper mantle lithospheric structure in the transition zone from stable Precambrian cratonic interior to passive continental margin beneath the Caledonian orogen and the Scandinavian Mountains in western Fennoscandia. An array of 59 synchronous long period and 220 broad-band MT sites was occupied in the summers of 2011 to 2013. We estimated MT transfer functions in the period range from 0.003 to 105 s. The Q-function multi-site multi-frequency analysis and the phase tensor were used to estimate strike and dimensionality of MT data. Dimensionality and strike analyses indicate generally 2-D behaviour of the data with 3-D effects at some sites and period bands. In this paper we present 2-D inversion of the data, 3-D inversion models are shown in the parallel paper. We choose to invert the determinant of the impedance tensor to mitigate 3-D effects in the data on our 2-D models. Seven crustal-scale and four lithospheric-scale 2-D models are presented. The resistive regions are images of the Archaean and Proterozoic basement in the east and thin Caledonian nappes in the west. The middle and lower crust of the Svecofennian province is conductive. The southern end of the Kittilä Greenstone Belt is seen in the models as a strong upper to middle crustal conductor. In the Caledonides, the highly conductive alum shales are observed along the Caledonian Thrust Front. The thickest lithosphere is in the Palaeoproterozioc Svecofennian Domain, not in the Archaean. The thickness of the lithosphere is around 200 km in the north and 300 km in the south-west.

  19. Joint Audio-Magnetotelluric and Passive Seismic Imaging of the Cerdanya Basin

    NASA Astrophysics Data System (ADS)

    Gabàs, A.; Macau, A.; Benjumea, B.; Queralt, P.; Ledo, J.; Figueras, S.; Marcuello, A.

    2016-06-01

    The structure of Cerdanya Basin (north-east of Iberian Peninsula) is partly known from geological cross sections, geological maps and vintage geophysical data. However, these data do not have the necessary resolution to characterize some parts of Cerdanya Basin such as the thickness of soft soil, geometry of bedrock or geometry of geological units and associated faults. For all these reasons, the main objective of this work is to improve this deficiency carrying out a detailed study in this Neogene basin applying jointly the combination of passive seismic methods (H/V spectral ratio and seismic array) and electromagnetic methods (audio-magnetotelluric and magnetotelluric method). The passive seismic techniques provide valuable information of geometry of basement along the profile. The maximum depth is located near Alp village with a bedrock depth of 500 m. The bedrock is located in surface at both sites of profile. The Neogene sediments present a shear-wave velocity between 400 and 1000 m/s, and the bedrock basement presents a shear-wave velocity values between 1700 and 2200 m/s. These results are used as a priori information to create a 2D resistivity initial model which constraints the inversion process of electromagnetic data. We have obtained a 2D resistivity model which is characterized by (1) a heterogeneous conductivity zone (<40 Ohm m) that corresponds to shallow part of the model up to 500 m depth in the centre of the profile. These values have been associated with Quaternary and Neogene sediments formed by silts, clays, conglomerates, sandstones and gravels, and (2) a deeper resistive zone (1000-3000 Ohm m) interpreted as Palaeozoic basement (sandstones, limestones and slates at NW and conglomerates and microconglomerates at SE). The resistive zone is truncated by a discontinuity at the south-east of the profile which is interpreted as the Alp-La Tet Fault. This discontinuity is represented by a more conductive zone (600 Ohm m approx.) and is explained as

  20. Joint interpretation of magnetotelluric, seismic, and well-log data in Hontomín (Spain)

    NASA Astrophysics Data System (ADS)

    Ogaya, Xènia; Alcalde, Juan; Marzán, Ignacio; Ledo, Juanjo; Queralt, Pilar; Marcuello, Alex; Martí, David; Saura, Eduard; Carbonell, Ramon; Benjumea, Beatriz

    2016-06-01

    Hontomín (N of Spain) hosts the first Spanish CO2 storage pilot plant. The subsurface characterization of the site included the acquisition of a 3-D seismic reflection and a circumscribed 3-D magnetotelluric (MT) survey. This paper addresses the combination of the seismic and MT results, together with the available well-log data, in order to achieve a better characterization of the Hontomín subsurface. We compare the structural model obtained from the interpretation of the seismic data with the geoelectrical model resulting from the MT data. The models correlate well in the surroundings of the CO2 injection area with the major structural differences observed related to the presence of faults. The combination of the two methods allowed a more detailed characterization of the faults, defining their geometry, and fluid flow characteristics, which are key for the risk assessment of the storage site. Moreover, we use the well-log data of the existing wells to derive resistivity-velocity relationships for the subsurface and compute a 3-D velocity model of the site using the 3-D resistivity model as a reference. The derived velocity model is compared to both the predicted and logged velocity in the injection and monitoring wells, for an overall assessment of the computed resistivity-velocity relationships. The major differences observed are explained by the different resolution of the compared geophysical methods. Finally, the derived velocity model for the near surface is compared with the velocity model used for the static corrections in the seismic data. The results allowed extracting information about the characteristics of the shallow unconsolidated sediments, suggesting possible clay and water content variations. The good correlation of the velocity models derived from the resistivity-velocity relationships and the well-log data demonstrate the potential of the combination of the two methods for characterizing the subsurface, in terms of its physical properties

  1. Joint Audio-Magnetotelluric and Passive Seismic Imaging of the Cerdanya Basin

    NASA Astrophysics Data System (ADS)

    Gabàs, A.; Macau, A.; Benjumea, B.; Queralt, P.; Ledo, J.; Figueras, S.; Marcuello, A.

    2016-09-01

    The structure of Cerdanya Basin (north-east of Iberian Peninsula) is partly known from geological cross sections, geological maps and vintage geophysical data. However, these data do not have the necessary resolution to characterize some parts of Cerdanya Basin such as the thickness of soft soil, geometry of bedrock or geometry of geological units and associated faults. For all these reasons, the main objective of this work is to improve this deficiency carrying out a detailed study in this Neogene basin applying jointly the combination of passive seismic methods ( H/V spectral ratio and seismic array) and electromagnetic methods (audio-magnetotelluric and magnetotelluric method). The passive seismic techniques provide valuable information of geometry of basement along the profile. The maximum depth is located near Alp village with a bedrock depth of 500 m. The bedrock is located in surface at both sites of profile. The Neogene sediments present a shear-wave velocity between 400 and 1000 m/s, and the bedrock basement presents a shear-wave velocity values between 1700 and 2200 m/s. These results are used as a priori information to create a 2D resistivity initial model which constraints the inversion process of electromagnetic data. We have obtained a 2D resistivity model which is characterized by (1) a heterogeneous conductivity zone (<40 Ohm m) that corresponds to shallow part of the model up to 500 m depth in the centre of the profile. These values have been associated with Quaternary and Neogene sediments formed by silts, clays, conglomerates, sandstones and gravels, and (2) a deeper resistive zone (1000-3000 Ohm m) interpreted as Palaeozoic basement (sandstones, limestones and slates at NW and conglomerates and microconglomerates at SE). The resistive zone is truncated by a discontinuity at the south-east of the profile which is interpreted as the Alp-La Tet Fault. This discontinuity is represented by a more conductive zone (600 Ohm m approx.) and is explained

  2. Megacam: A Wide-Field CCD Imager for the MMT and Magellan

    NASA Astrophysics Data System (ADS)

    McLeod, Brian; Geary, John; Conroy, Maureen; Fabricant, Daniel; Ordway, Mark; Szentgyorgyi, Andrew; Amato, Stephen; Ashby, Matthew; Caldwell, Nelson; Curley, Dylan; Gauron, Thomas; Holman, Matthew; Norton, Timothy; Pieri, Mario; Roll, John; Weaver, David; Zajac, Joseph; Palunas, Povilas; Osip, David

    2015-04-01

    Megacam is a large-format optical camera that can be operated at the f/5 Cassegrain foci of the MMT on Mount Hopkins, Arizona, and the Magellan Clay telescope at Las Campanas Observatory, Chile. Megacam's focal plane is composed of 36 closely packed e2v CCD42-90 CCDs, each with 2048 × 4608 pixels, assembled in an 18,432 × 18,432 array. Two additional CCD42-90s are provided for autoguiding and focus control. The CCDs have 13.5 μm square pixels that subtend 0 \\overset{''}{.} 08 at the f/5 foci, yielding a 25' × 25' field-of-view. The camera system includes a focal plane shutter, two filter wheels, two liquid nitrogen reservoirs, a central chamber that holds the CCD mosaic array, and two electronics boxes. Megacam is equipped with a variety of broadband and narrowband filters. Software features include automatic calculation of twilight flat exposure times.

  3. Magnetotelluric investigation of the geothermal anomaly in Hailin, Mudanjiang, northeastern China

    NASA Astrophysics Data System (ADS)

    Zhang, Lili; Hao, Tianyao; Xiao, Qibin; Wang, Jie; Zhou, Liang; Qi, Min; Cui, Xiangpan; Cai, Ningxiao

    2015-07-01

    To study the occurrence conditions and locations of geothermal bodies in Hailin, Mudanjiang, northeastern China, we conducted a magnetotelluric investigation to delineate the electrical conductivity structure of the area on three parallel profiles. The area to the west of the Mudanjiang Fault lies in the Hailang sag of the Ning'an Basin. The data were processed using the mutual reference technique, static shift correction, and structural strike and dimensionality analysis based on tensor decomposition. Moreover, a modified anisotropic-diffusion-based method was used to suppress noise for the magnetotelluric time series data. This method retains the advantages of conventional anisotropic diffusion and is superior in its discrimination ability. The method is characteristic not only of the inherited features such as intra-region smoothing and edge preservation, but also of the adaptive selection of the diffusion coefficient. Data analysis revealed that the electrical resistivity structure can be approximated by a two-dimensional characterization. Two-dimensional inversion and rendering visualization show that a highly resistive granite basement is covered with conductive sedimentary layers and that a relatively low-resistivity anomalous structure with a resistivity of approximately 100-600 Ω·m is imbedded in the high-resistivity background. The anomalous structure has a narrow top and a wide bottom (the bottom depth is at least 3500 m). The shape and electrical features of the structure indicate favorable storage space for hot subsurface water. Fault activities and magma intrusion may result in the fractures of the basement, which are filled with hot water and thus produce the relatively low resistivity. Based on a comprehensive analysis, we infer that the structure is indicative of a geothermal reservoir. An exploratory well drilled near the structure confirms the occurrence of high temperatures. Several geological factors (cap rock, basement, and major faults

  4. Three-Dimensional Magnetotelluric Inversion: An Introductory Guide for Developers and Users

    NASA Astrophysics Data System (ADS)

    Siripunvaraporn, Weerachai

    2012-01-01

    In the last few decades, the demand for three-dimensional (3-D) inversions for magnetotelluric data has significantly driven the progress of 3-D codes. There are currently a lot of new 3-D inversion and forward modeling codes. Some, such as the WSINV3DMT code of the author, are available to the academic community. The goal of this paper is to summarize all the important issues involving 3-D inversions. It aims to show how inversion works and how to use it properly. In this paper, I start by describing several good reasons for doing 3-D inversion instead of 2-D inversion. The main algorithms for 3-D inversion are reviewed along with some comparisons of their advantages and disadvantages. These algorithms are the classical Occam's inversion, the data space Occam's inversion, the Gauss-Newton method, the Gauss-Newton with the conjugate gradient method, the non-linear conjugate gradient method, and the quasi-Newton method. Other variants are based on these main algorithms. Forward modeling, sensitivity calculations, model covariance and its parallel implementation are all necessary components of inversions and are reviewed here. Rules of thumb for performing 3-D inversion are proposed for the benefit of the 3-D inversion novice. Problems regarding 3-D inversions are discussed along with suggested topics for future research for the developers of the next decades.

  5. Two and three dimensional inversion of magnetotelluric data: Annual report No. 2

    SciTech Connect

    Booker, J.R.

    1988-02-01

    We have developed an efficient iterative inversion method applicable to both 2 and 3-D magnetotelluric data. The method approximates horizontal derivative terms with their values calculated from the fields of the previous iteration. The equations at each horizontal coordinate then become uncoupled and 1-D with an added term containing the effects of the horizontal derivatives. At each iteration this allows separate 1-D inversions for the conductivity profile beneath each measurement site. Resultant profiles are interpolated to form a new multi-dimensional model for which the fields are calculated. Residuals to this new model are used in the next iteration. The method is very fast, as partial derivatives are calculated for 1-D problems only and computation time grows only linearly with the number of sites of data inverted. Preliminary tests with 2-D data show very promising results. Some practial problems remain in application of the algorithm to real 2-D data. We are requesting continued support to resolve these questions and to extend the method to 3-D.

  6. Lithology-derived structure classification from the joint interpretation of magnetotelluric and seismic models

    USGS Publications Warehouse

    Bedrosian, P.A.; Maercklin, N.; Weckmann, U.; Bartov, Y.; Ryberg, T.; Ritter, O.

    2007-01-01

    Magnetotelluric and seismic methods provide complementary information about the resistivity and velocity structure of the subsurface on similar scales and resolutions. No global relation, however, exists between these parameters, and correlations are often valid for only a limited target area. Independently derived inverse models from these methods can be combined using a classification approach to map geologic structure. The method employed is based solely on the statistical correlation of physical properties in a joint parameter space and is independent of theoretical or empirical relations linking electrical and seismic parameters. Regions of high correlation (classes) between resistivity and velocity can in turn be mapped back and re-examined in depth section. The spatial distribution of these classes, and the boundaries between them, provide structural information not evident in the individual models. This method is applied to a 10 km long profile crossing the Dead Sea Transform in Jordan. Several prominent classes are identified with specific lithologies in accordance with local geology. An abrupt change in lithology across the fault, together with vertical uplift of the basement suggest the fault is sub-vertical within the upper crust. ?? 2007 The Authors Journal compilation ?? 2007 RAS.

  7. Comparison of In Situ Polymerization and Solution-Dispersion Techniques in the Preparation of Polyimide/Montmorillonite (MMT) Nanocomposites

    PubMed Central

    Ahmad, Mansor Bin; Gharayebi, Yadollah; Salit, Mohd. Sapuan; Hussein, Mohd. Zobir; Shameli, Kamyar

    2011-01-01

    In this paper, Polyimide/Montmorillonite Nanocomposites (PI/MMT NCs), based on aromatic diamine (4-Aminophenyl sulfone) (APS) and aromatic dianhydride (3,3′,4,4′-benzophenonetetracarboxylic dianhydride) (BTDA) were prepared using in situ polymerization and solution-dispersion techniques. The prepared PI/MMT NCs films were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), transmission electron microscopy (TEM) and thermogravimetric analysis (TGA). The XRD results showed that at the content of 1.0 wt % Organo Montmorillonite (OMMT) for two techniques and 3.0 wt % OMMT for the in situ polymerization technique, the OMMT was well-intercalated, exfoliated and dispersed into polyimide matrix. The OMMT agglomerated when its amount exceeded 10 wt % and 3.0 wt % for solution-dispersion and in situ polymerization techniques respectively. These results were confirmed by the TEM images of the prepared PI/MMT NCs. The TGA thermograms indicated that thermal stability of prepared PI/MMT NCs were increased with the increase of loading that, the effect is higher for the samples prepared by in situ polymerization technique. PMID:22016643

  8. Application of Mixture of Gaussian Clustering on Joint Facies Interpretation of Seismic and Magnetotelluric Sections

    NASA Astrophysics Data System (ADS)

    Shahrabi, Mohammad Ali; Hashemi, Hosein; Hafizi, Mohammad Kazem

    2016-02-01

    Seismic and magnetotelluric (MT) methods are the most applicable geophysical methods in exploration of hydrocarbon resources. In this paper, mixture of Gaussian clustering is used to combine seismic and MT images under the scheme of Expectation/Maximization (EM) algorithm. Pre-Stack Depth Migration (PSDM) velocity, Root Mean Square (RMS) velocity and vertical gradient of RMS velocity of seismic and resistivity model of MT along 19.3 km MUN-21 profile in Munir Block that has been located in Southwest of Iran in Dezful embayment over the Seh-Qanat anticline are applied. The anticline is the most important oil trap of this area. The Expectation/Maximization (EM) method that has been applied includes: (1) creation of data vectors from the seismic and MT images using image processing techniques, (2) normalizing and mapping using Principal Component Analysis (PCA) procedure (3) unsupervised learning of dataset matrix, (4) setting the matrix in Expectation/Maximization (EM) iteration algorithm (5) remapping to physical space. The final model consists fof six classes which could be given to eight formations that belong to Eocene to Neocomian geological age. Pre-Stack Depth Migration (PSDM) velocity model obtained from seismic study on Seh-Qanat anticline only detected 2 horizons of formations, Asmari and Sarvak Formations; however, the current methodology introduces subdivision anticline into six classes by matching it to the log information of Seh-Qanat Deep-1 (SQD-1) borehole where it was excavated over the anticline with total depth of 2876 m.

  9. Spatial and temporal characterization of CO2 storage sites using magnetotellurics

    NASA Astrophysics Data System (ADS)

    Ledo, J.; Queralt, P.; Marcuello, A.; Roca, E.; Rubinat, M.

    2009-04-01

    Integration of different geophysical, geological and geochemical methods will play a key role for the spatial and temporal characterization of underground CO2 storage sites. Among the geophysical techniques the magnetotelluric method (MT) may help on both, site characterization and monitoring of the CO2 plume, mainly on deep saline reservoirs. In this work we present the characterization of a salt diapir in southern Spain using MT data. This diaper does not satisfy the conditions to be a future reservoir due to the absence of a good lithological seal, but can be use as a natural analog to determine the validity of different geophysical methods. In total 34 MT sites were acquired along a 15 km profile. Once the data has been analyzed, inverted and integrated with surface geological data a simulated investigation for monitoring the CO2 has been carried out. In this simulation the CO2 has been located at the base of the Jurassic to Turonnian carbonates and marls increasing the resistivity of the model. Several tests varying the resistivity and the amount of the CO2 as well as the number of MT sites used will be show.

  10. Long regional magnetotelluric profile crossing geotectonic structures of central Poland

    NASA Astrophysics Data System (ADS)

    Stefaniuk, M.; Pokorski, J.; Wojdyla, M.

    2009-04-01

    Introduction The magnetotelluric survey was made along a regional profile, which runs across Poland from south-west to north-east during 2005-2006 years. The profile crosses major geological structures of Central Poland, including the Variscan Externides and Variscan foredeep, the Transeuropean Suture Zone and the marginal zone of East European Craton. The main objectives of the project include identification of sub-Zechstein sedimentary structures and evaluation of resistivity distribution within the deep crust, especially at the contact of East European Precambrian Craton and Central Europe Paleozoic structures. The length of the profile is about 700 km; 161 deep magnetotelluric sounding sites were made with a medium spacing of about 4 km. Data acquisition and processing The recording of the components of natural electromagnetic field was made with a broad range of frequencies, varying from 0.0003 Hz up to 575 Hz with use of MT-1 system of Electromagnetic Instruments Incorporation. This frequency band allowed obtaining the information about geology ranging from a few dozen meters to approximately 100 km, depending on the vertical distribution of the resistivity inside geological medium. To reduce the electromagnetic noise, magnetic and electric remote reference was applied. A remote reference site was located at a distance of over 100 km of field sites. Processing of the recorded data included the estimation of the components of impedance tensor (Zxx, Zxy, Zyx and Zyy ), with use of robust type procedures. The components of the impedance tensor allowed in a subsequent step for calculation of field curves for two orientations of the measurement system (XY - described further as the TM mode and YX - TE mode) and additional parameters of the medium like skew, strike, pole diagrams etc. Recording of the vertical component of electromagnetic field (Hz) allowed calculation of tipper parameter T. Magnetotelluric soundings interpretation Geophysical interpretation of MT

  11. Characterization of the Pyrenean lithosphere using new long period magnetotelluric data

    NASA Astrophysics Data System (ADS)

    Campanyà, Joan; Ledo, Juanjo; Queralt, Pilar; Marcuello, Alex; Muñoz, Josep Anton; Liesa, Montserrat

    2010-05-01

    New magnetotelluric (MT) data has been acquired along a N-S profile of 180 km length that cross the Pyrenean range. The new MT data are complemented with old MT data registered at the same profile 15 years ago. In this work we have 15 old MT data with periods ranging from 0.0128 s to 2000 s and 8 new MT data with periods ranging from 0.001 s to 20000 s. The new data allows us to arrive deeper and determine the lithosphere resistivity structure with more precision up to 150 km depth. Moreover, the final geoelectric model has been obtained using 2D inversion procedures. The previous model was obtained by direct modelling, following a trial and error approach. Analyses of the MT data using the Groom and Bailey decomposition method, as well as the use of the tensor invariants corroborate the validity of assuming regional 2D structures. The strike direction of the electrical structures is E-W, parallel to the Pyrenean range. The final model obtained shows a deep large structure with low electrical resistivity values between Iberian and European plates that can be associated to the subduction of the Iberian plate. We suggest, that the cause of this low resistivity values is the existence of partial melting of the Iberian lower crust below the European one. Sensitivity tests prove that resistivity in this structure is not homogeneous. A vertical gradient is observed between the top and the bottom of the structure, having the top low electrical resistivity values, around 3 Ohm•m, than the bottom that present values between 10 Ohm•m and 56 Ohm•m. At the base of the model appears another low resistivity zone associated with the asthenosphere. The lithosphere asthenosphere boundary depth is different for the two plates studied. The sensitivity tests show that the depth for Iberian plate is 80 ± 20 km and 120 ± 15 km for the European plate. The different depths of these limits show that European plate is thicker. The geoelectric model is compared with several

  12. The application of artificial neural networks to magnetotelluric time-series analysis

    NASA Astrophysics Data System (ADS)

    Manoj, C.; Nagarajan, Nandini

    2003-05-01

    Magnetotelluric (MT) signals are often contaminated with noise from natural or man-made processes that may not fit a normal distribution or are highly correlated. This may lead to serious errors in computed MT transfer functions and result in erroneous interpretation. A substantial improvement is possible when the time-series are presented as clean as possible for further processing. Cleaning of MT time-series is often done by manual editing. Editing of magnetotelluric time-series is subjective in nature and time consuming. Automation of such a process is difficult to achieve by statistical methods. Artificial neural networks (ANNs) are widely used to automate processes that require human intelligence. The objective here is to automate MT long-period time-series editing using ANN. A three-layer feed-forward artificial neural network (FANN) was adopted for the problem. As ANN-based techniques are computationally intensive, a novel approach was made, which involves editing of five simultaneously measured MT time-series that have been subdivided into stacks (a stack=5 × 256 data points). Neural network training was done at two levels. Signal and noise patterns of individual channels were taught first. Five channel parameters along with interchannel correlation and amplitude ratios formed the input for a final network, which predicts the quality of a stack. A large database (5000 traces for pattern training and 900 vectors for interchannel training) was prepared to train the network. There were two error parameters to minimize while training: training error and testing error. Training was stopped when both errors were below an acceptable level. The sensitivity of the neural network to the signal-to-noise ratio and the relative significance of its inputs were tested to ensure that the training was correct. MT time-series from four stations with varying degrees of noise contamination were used to demonstrate the application of the network. The application brought out

  13. Advances in applications of magnetotellurics to hydrocarbon exploration in Papua New Guinea

    SciTech Connect

    Christopherson, K.R.

    1995-06-01

    More than 800 Magnetotelluric (MT) stations and EMAP dipoles have been acquired in Papua New Guinea (PNG) since 1988. The use and understanding of this non-seismic method has developed because the lucrative petroleum province of the Highlands Fold Belt. Exploration in this area precludes conventional seismic acquisition owing to outcropping limestone which is karstified and more than 3000 feet (1 km) thick in most areas. MT acquisition has expanded from acquiring single-site or dual-site data using standard wire-link communication to acquiring five stations simultaneously, with communications via radio telemetry. This has resulted in higher production rates, better quality data, and more flexible emplacement of station locations. Design modifications to acquisition equipment has resulted in lighter gear which acquires data with higher signal-to-noise ratio, leading to more reliable interpretations. Advances in computer modeling, primarily through Geotools software, along with better understanding of the structural province and integration with geologists` information, have improved the usability of the interpreted data. The last seven years have seen several wells drilled of which many are now in production. MT has been acquired at many of these locations, and continues to be a advanced exploration tool. Case histories will demonstrate the effectiveness of exploration using MT and other electrical methods.

  14. Regularized inversion of controlled source audio-frequency magnetotelluric data in horizontally layered transversely isotropic media

    NASA Astrophysics Data System (ADS)

    Zhou, Jianmei; Wang, Jianxun; Shang, Qinglong; Wang, Hongnian; Yin, Changchun

    2014-04-01

    We present an algorithm for inverting controlled source audio-frequency magnetotelluric (CSAMT) data in horizontally layered transversely isotropic (TI) media. The popular inversion method parameterizes the media into a large number of layers which have fixed thickness and only reconstruct the conductivities (e.g. Occam's inversion), which does not enable the recovery of the sharp interfaces between layers. In this paper, we simultaneously reconstruct all the model parameters, including both the horizontal and vertical conductivities and layer depths. Applying the perturbation principle and the dyadic Green's function in TI media, we derive the analytic expression of Fréchet derivatives of CSAMT responses with respect to all the model parameters in the form of Sommerfeld integrals. A regularized iterative inversion method is established to simultaneously reconstruct all the model parameters. Numerical results show that the inverse algorithm, including the depths of the layer interfaces, can significantly improve the inverse results. It can not only reconstruct the sharp interfaces between layers, but also can obtain conductivities close to the true value.

  15. Salt, Sediments and Seawater: Marine Magnetotellurics in the Gulf of Mexico

    NASA Astrophysics Data System (ADS)

    Weiss, C.; Key, K.; Constable, S.

    2002-12-01

    The Smackover and Louann salt formations are distinguishing features of the Gulf of Mexico which not only provide clues to the tectonic evolution of the Gulf, but also play a critical role in the formation of traps for hydrocarbon reservoirs. However, the challenge of mapping these features is only partially met by existing seismic methods: the top of salt (TOS) is usually well resolved while the base of salt (BOS) is remarkably less so. Owing to the high contrast in electrical conductivity between salt and the surrounding sediments, electromagnetic methods such as magnetotellurics (MT) are promising techniques for minimizing the uncertainty in mapping allocthonous salt structures. Futhermore, the high conductivity of the seawater invites speculation on the usefulness of vertical electric field measurements in TOS/BOS characterization. Thus, we present results from a series of 3D numerical modeling experiments of electromagnetic induction over a ``realistic'' salt body: a 3D seismic--derived volume representing the Gemini salt structure, located beneath 1000m of water in the Mississippi Canyon, Gulf of Mexico. Results are compared to a collection of 34 broadband (T= 1--5000 s) MT datasets collected in three surveys over the structure between 1998 and 2001. Previously obtained 2D inversion results of the observed data are validated by 2D inversion of the fully 3D synthetic model response.

  16. Three-dimensional controlled-source electromagnetic and magnetotelluric joint inversion

    NASA Astrophysics Data System (ADS)

    Commer, Michael; Newman, Gregory A.

    2009-09-01

    The growing use of the controlled-source electromagnetic method (CSEM) and magnetotellurics (MT) for exploration applications has been driving the development of data acquisition technologies, and three-dimensional (3-D) modelling and imaging techniques. However, targeting increasingly complex geological environments also further enhances the problems inherent in large-scale inversion, such as non-uniqueness and resolution issues. In this paper, we report on two techniques to mitigate these problems. We use 3-D joint CSEM and MT inversion to improve the model resolution. To avoid the suppression of the resolution capacities of one data type, and thus to balance the use of inherent, and ideally complementary information content, different data reweighting schemes are proposed. Further, a hybrid model parametrization approach is presented, where traditional cell-based model parameters are used simultaneously within a parametric inversion. The idea is to limit the non-uniqueness problem, typical for 3-D imaging problems, in order to allow for a more focusing inversion. The methods are demonstrated using synthetic data generated from models with a strong practical relevance.

  17. Three-dimensional controlled-source electromagnetic and magnetotelluric joint inversion

    NASA Astrophysics Data System (ADS)

    Commer, M.; Newman, G. A.

    2009-12-01

    The growing use of the controlled-source electromagnetic method (CSEM) and magnetotellurics (MT) for exploration applications has been driving the development of data acquisition technologies, and three-dimensional (3D) modeling and imaging techniques. However, targeting increasingly complex geological environments also further enhances the problems inherent in large-scale inversion, such as non-uniqueness and resolution issues. In this paper, we report on two techniques to mitigate these problems. We use 3D joint CSEM and MT inversion to improve the model resolution. To avoid the suppression of the resolution capacities of one data type, and thus to balance the use of inherent, and ideally complementary information content, different data re-weighting schemes are proposed. Further, a hybrid model parametrization approach is presented, where traditional cell-based model parameters are used simultaneously within a parametric inversion. The idea is to limit the non-uniqueness problem, typical for 3D imaging problems, in order to allow for a more focusing inversion. The methods are demonstrated using synthetic data generated from models with a strong practical relevance.

  18. Three-dimensional controlled-source electromagnetic and magnetotelluric joint inversion

    SciTech Connect

    Commer, M.; Newman, G.A.

    2009-02-15

    The growing use of the controlled-source electromagnetic method (CSEM) and magnetotellurics (MT) for exploration applications has been driving the development of data acquisition technologies, and three-dimensional (3-D) modeling and imaging techniques. However, targeting increasingly complex geological environments also further enhances the problems inherent in large-scale inversion, such as non-uniqueness and resolution issues. In this paper, we report on two techniques to mitigate these problems. We use 3-D joint CSEM and MT inversion to improve the model resolution. To avoid the suppression of the resolution capacities of one data type, and thus to balance the use of inherent, and ideally complementary information content, different data reweighting schemes are proposed. Further, a hybrid model parameterization approach is presented, where traditional cell-based model parameters are used simultaneously within a parametric inversion. The idea is to limit the non-uniqueness problem, typical for 3-D imaging problems, in order to allow for a more focusing inversion. The methods are demonstrated using synthetic data generated from models with a strong practical relevance.

  19. Magnetotelluric Data, Mid Valley, Nevada Test Site, Nevada.

    SciTech Connect

    Jackie M. Williams; Erin L. Wallin; Brian D. Rodriguez; Charles R. Lindsay; and Jay A. Sampson

    2007-08-15

    The United States Department of Energy (DOE) and the National Nuclear Security Administration (NNSA) at their Nevada Site Office (NSO) are addressing ground-water contamination resulting from historical underground nuclear testing through the Environmental Management (EM) program and, in particular, the Underground Test Area (UGTA) project. One issue of concern is the nature of the somewhat poorly constrained pre-Tertiary geology and its effects on ground-water flow. Ground-water modelers would like to know more about the hydrostratigraphy and geologic structure to support a hydrostratigraphic framework model that is under development for the Rainier Mesa/Shoshone Mountain Corrective Action Unit (CAU) (Bechtel Nevada, 2006). During 2003, the U.S. Geological Survey (USGS), in cooperation with the DOE and NNSA-NSO, collected and processed data at the Nevada Test Site in and near Yucca Flat (YF) to help define the character, thickness, and lateral extent of the pre-tertiary confining units. We collected 51 magnetotelluric (MT) and audio-magnetotelluric (AMT), stations for that research (Williams and others, 2005a, 2005b, 2005c, 2005d, 2005e, 2005f). In early 2005 we extended that research with 26 additional MT data stations (Williams and others, 2006), located on and near Rainier Mesa and Shoshone Mountain (RM-SM). The new stations extended the area of the hydrogeologic study previously conducted in Yucca Flat. This work was done to help refine what is known about the character, thickness, and lateral extent of pre-Tertiary confining units. In particular, a major goal was to define the upper clastic confining unit (UCCU). The UCCU is comprised of late Devonian to Mississippian siliciclastic rocks assigned to the Eleana Formation and Chainman Shale. The UCCU underlies the Yucca Flat area and extends westward towards Shoshone Mountain, southward to Buckboard Mesa, and northward to Rainier Mesa. Late in 2005 we collected another 14 MT stations in Mid Valley and in

  20. Magnetotelluric Data, Mid Valley, Nevada Test Site, Nevada

    USGS Publications Warehouse

    Williams, Jackie M.; Wallin, Erin L.; Rodriguez, Brian D.; Lindsey, Charles R.; Sampson, Jay A.

    2007-01-01

    Introduction The United States Department of Energy (DOE) and the National Nuclear Security Administration (NNSA) at their Nevada Site Office (NSO) are addressing ground-water contamination resulting from historical underground nuclear testing through the Environmental Management (EM) program and, in particular, the Underground Test Area (UGTA) project. One issue of concern is the nature of the somewhat poorly constrained pre-Tertiary geology and its effects on ground-water flow. Ground-water modelers would like to know more about the hydrostratigraphy and geologic structure to support a hydrostratigraphic framework model that is under development for the Rainier Mesa/Shoshone Mountain Corrective Action Unit (CAU). During 2003, the U.S. Geological Survey (USGS), in cooperation with the DOE and NNSA-NSO, collected and processed data at the Nevada Test Site in and near Yucca Flat (YF) to help define the character, thickness, and lateral extent of the pre-Tertiary confining units. We collected 51 magnetotelluric (MT) and audio-magnetotelluric (AMT), stations for that research. In early 2005 we extended that research with 26 additional MT data stations, located on and near Rainier Mesa and Shoshone Mountain (RM-SM). The new stations extended the area of the hydrogeologic study previously conducted in Yucca Flat. This work was done to help refine what is known about the character, thickness, and lateral extent of pre-Tertiary confining units. In particular, a major goal was to define the upper clastic confining unit (UCCU). The UCCU is comprised of late Devonian to Mississippian siliciclastic rocks assigned to the Eleana Formation and Chainman Shale. The UCCU underlies the Yucca Flat area and extends westward towards Shoshone Mountain, southward to Buckboard Mesa, and northward to Rainier Mesa. Late in 2005 we collected another 14 MT stations in Mid Valley and in northern Yucca Flat basin. That work was done to better determine the extent and thickness of the UCCU near

  1. Synthesis and characterization of low-generation polyamidoamine (PAMAM) dendrimer-sodium montmorillonite (Na-MMT) clay nanocomposites.

    PubMed

    Liyanage, Amila U; Ikhuoria, Esther U; Adenuga, Adeniyi A; Remcho, Vincent T; Lerner, Michael M

    2013-04-15

    Polymer-inorganic nanocomposites are a recently developed class of materials that have altered physical or chemical properties with respect to the pure polymer, inorganic host, or their micro- and macrocomposites. Lower generation (G0.0-2.0) polyamidoamine (PAMAM) dendrimer/sodium montmorillonite (Na-MMT) nanocomposites were synthesized in a solution-phase exfoliation adsorption reaction. These are the first reports of the G0.0/ and G1.0/Na-MMT nanocomposites and of a structurally-ordered G2.0/Na-MMT. The materials were characterized using powder X-ray diffraction (PXRD), thermogravimetric analysis (TGA), and Fourier transform infrared spectroscopy (FTIR). PAMAM characteristics at acidic and basic aqueous media were studied using capillary zone electrophoresis (CZE). Pseudospherical PAMAM dendrimers in aqueous medium attain a highly flattened conformation within the confined space between MMT sheets upon nanocomposite formation. The nanocomposite structure depends on the PAMAM generation and the starting dendrimer/organic composition. G0.0 always forms monolayer structures (d = 0.42 nm), while G2.0 forms monolayer structure, mixed phase, and bilayer structures (d = 0.84 nm) at lower, intermediate, and higher organic content, respectively, showing an interesting monolayer to bilayer transition. G1.0 showed an intermediate behavior, with monolayer to mixed-phase transition at the reactant ratios studied. This monolayer arrangement of PAMAM/clay nanocomposites is reported for the first time. Maximum organic contents of G0.0 monolayer and G2.0 bilayer nanocomposites were ∼7% and ∼14%, respectively. Gallery expansions were similar to those observed with linear polymer intercalates, but the packing fractions (0.31-0.32) were 2-3 times lower. At acidic pH, the nanocomposites forming only monolayer structures are obtained, indicating a stronger electrostatic attraction between MMT and protonated PAMAM, and these nanocomposites formed more slowly and were more ordered

  2. A novel method for fabricating hybrid biobased nanocomposites film with stable fluorescence containing CdTe quantum dots and montmorillonite-chitosan nanosheets.

    PubMed

    Guo, Yawen; Ge, Xuesong; Guan, Jing; Wu, Lin; Zhao, Fuhua; Li, Hui; Mu, Xindong; Jiang, Yijun; Chen, Aibing

    2016-07-10

    A method was presented for fabricating the fluorescent nanocomposites containing CdTe quantum dots (QDs) and montmorillonite (MMT)-chitosan (CS). MMT-CS/CdTe QDs nanocomposites were prepared via a simple, versatile and robust approach combination of covalent and electrostatic assembly methods (Scheme 1). The negatively charged MMT was initially modified with positively charged CS through electrostatic assembly, followed by incorporation of CdTe-QDs into the MMT-CS nanosheets by covalent connections between the amino groups of CS and the carboxylic acid groups of thioglycollic acid (TGA). The X-ray diffraction (XRD), High resolution transmission electron microscopy (HRTEM), scanning electron microscopy (SEM) and the FTIR were used to prove the QDs have intercalated into the MMT-CS matrix. The fluorescence emission spectra showed that the MMT-CS/CdTe QDs nanocomposites had the best fluorescence intensity compared with the bare CdTe QDs and CS-QDs. PMID:27106146

  3. Three-dimensional Magnetotelluric Modeling of the Pohukuloa Training Area, Hawaii Island

    NASA Astrophysics Data System (ADS)

    Thomas, D. M.; Lienert, B. R.; Wallin, E.

    2015-12-01

    We report the results of 3D modeling of magnetotelluric (MT) data collected in the Pohakuloa Training Area (PTA) on the saddle between Mauna Loa and Mauna Kea volcanoes on Hawaii Island. We have previously used lower frequency MT data to construct 1D and 2D resistivity profiles in this area and confirmed the presence of a low-resistivity region at depths of about 2 km. One of our drill holes in PTA had previously encountered temperatures of 150 C at a similar depth. However, our 1D and 2D models were unable to fit features of the data that we suspected were due to 3D variations in subsurface resistivity. For the 3D modeling, we reprocessed the higher frequency data (1 kHz sampling rate) which were available at all 20 sites. We were then able to obtain complex impedances at frequencies of 0.5-500 Hz to use for the 3D inversion. We used Siripunvaraporn's 3D inversion method to obtain resistivities in a rectangular array of 0.5x0.5x0.25 km blocks spanning the areal extent of the stations down to a depth of 2.5 km. The results confirmed that much of the anomalous data could be explained by near-surface 3D variations in resistivity. The underlying conductor of 5-10 ohm-m at 2 km depth now appears to extend over the entire survey area.

  4. Geoelectrical dimensionality analyses in Sumatran Fault (Aceh segment) using magnetotelluric phase tensor

    NASA Astrophysics Data System (ADS)

    Prihantoro, Rudy; Nurhasan, Sutarno, Doddy; Ogawa, Yasuo; Priahadena, Has; Fitriani, Dini

    2014-03-01

    Earth electrical / geoelectrical conductivity may vary in any direction in a complex earth model. When conductivity only varying within one direction such as depth, it is considered as an one-dimensional (1-D) structure model. Two-dimensional (2-D) and three-dimensional (3-D) structure have more degrees of conductivity variation. In magnetotelluric (MT) surveys localized heterogeneities in conductivity near the Earth's surface distort the electromagnetic (EM) response produced by the underlying or 'regional' conductivity structure under investigation. Several attempts had been done to remove this distortion effect in measured MT transfer functions (impedances tensor) by a series of techniques and general conductivity models of increasing complexity. The most common technique are Bahr's method and Groom-Bailey decompositions, that is restricted by assumption of two dimensional (2D) regional conductivity structure. MT phase tensor technique proposed by Caldwell et al. (2004) requires no assumption about the dimensionality of the regional conductivity structure and is applicable where both the heterogeneity and the regional conductivity structure are 3-D. Here, we examine the dimensionality analyses using the MT phase tensor to measured data of Sumatran Fault (SF) Aceh segment that we've collected during July 2012. A small value of phase tensor dimensionality indicator (β) was found along the profile. This result indicate a strong a two dimensionality of regional conductivity structure of SF Aceh segment.

  5. Magnetotelluric monitoring of a fluid injection: Example from an enhanced geothermal system

    NASA Astrophysics Data System (ADS)

    Peacock, J. R.; Thiel, S.; Reid, P.; Heinson, G.

    2012-09-01

    Enhanced geothermal systems (EGS) are on the verge of becoming commercially viable for power production, where advancements in subsurface characterization are imperative to develop EGS into a competitive industry. Theory of an EGS is simple, pump fluids into thermally enhanced lithology and extract the hot fluids to produce energy. One significant complication in EGS development is estimating where injected fluids flow in the subsurface. Micro-seismic surveys can provide information about where fractures opened, but not fracture connectivity nor fluid inclusion. Electromagnetic methods are sensitive to conductivity contrasts and can be used as a supplementary tool to delineate reservoir boundaries. In July, 2011, an injection test for a 3.6 km deep EGS at Paralana, South Australia was continuously monitored by both micro-seismic and magnetotellurics (MT). Presented are the first results from continuous MT measurements suggesting transient variations in subsurface conductivity structure generated from the introduction of fluids at depth can be measured. Furthermore, phase tensor representation of the time dependent MT response suggests fluids migrated in a NE direction from the injection well. Results from this experiment supports the extension of MT to a monitoring tool for not only EGS but other hydraulic stimulations.

  6. A magnetotelluric survey in the northern Bolivian Altiplano

    SciTech Connect

    Ritz, M. ); Bondoux, F. ); Herail, G.; Sempere, T. )

    1991-03-01

    Magnetotelluric (MT) measurements were performed at 9 sites on the northern Bolivian Altiplano in an attempt to determine thicknesses of the Cainozoic sedimentary infill and to characterize the underlying crust. At some of the sites the MT soundings show complications due to static shift effects caused by local, surficial heterogeneities. Preliminary one-dimensional (1D) modeling of the data based on the impedance tensor determinant parameters was undertaken for sites considered to be free of static effects, and was followed by 2D modeling. The model obtained indicates, from the surface downward, three important geoelectrical units, namely (1) a very low-resistivity layer (1-6 ohm-m) consisting of late Cainozoic volcanic rocks and/or Tertiary-Cretaceous sedimentary rocks 1-4 km in thickness, (2) a crustal resistive zone (about 200 ohm-m), and (3) a lower crustal or uppermost mantle conductor (less than 10 ohm-m) at depths of 40-45 km which might be related to partial melting. This model is consistent with the geological model according to which the Altiplano formed as a synorogenic basin showing abrupt changes in depositional thicknesses across thrust faults.

  7. Magnetotelluric models of the Roosevelt Hot Springs thermal area, Utah

    SciTech Connect

    Wannamaker, P.E.; Ward, S.H.; Hohmann, G.W.; Sill, W.R.

    1980-09-01

    The Roosevelt Hot Springs (RHS) thermal area, which includes a hotwater-dominated fracture zone prospect, near the eastern margin of the Basin-Range tectonic province, conceivably possesses a whole family of resistivity structures that includes the following: deep hot brine reservoirs, deep-seated partially molten heat sources in the crust or upper mantle that drive the convective system, near-surface hydrothermal alteration zones, wet sedimentary fill in valleys, and a regional, apparently one-dimensional resistivity profile of the crust and upper mantle. This complex resistivity makeup, particular to RHS but probably similar to that at other geothermal areas in the Great Basin, must be treated as being fully three-dimensional (3-D). In an attempt to understand these structures, broadband (10/sup -3/ to 10/sup -2/ Hz) tensor magnetotelluric (MT) data were obtained including apparent resistivities (rho/sub a/), impedance phases (phi) and vertical magnetic field transfer functions for 93 sites in the vicinity of this resource area.

  8. Ophiolite emplacement in NE Oman: constraints from magnetotelluric sounding

    NASA Astrophysics Data System (ADS)

    Thiel, S.; Heinson, G.; Gray, D. R.; Gregory, R. T.

    2009-03-01

    Magnetotelluric (MT) data have been acquired across the Samail Ophiolite, Oman mountains, along a 115km transect in January 2005. Twenty-five MT stations were deployed approximately every 4km along a profile perpendicular to the coastline near Muscat. The profile extends from the Huw'l/Meeh subwindow in the northwestern part of the profile and crosses the Saih Hatat window, a Tertiary domal culmination that folds a major NE-facing recumbent fold nappe, and ends along the southern boundary between the Dasir and Ibra ophiolite blocks. The survey aimed to investigate the tectonic evolution of the emplacement of the Samail Ophiolite by delineating major faults and geological boundaries on a crustal scale. The data shows complex behaviour with the influence of static shift effects and anomalously high phases exceeding 90°. Phase tensor analysis and 3-D forward modelling hint that the upper plate-lower plate (UP-LP) shear zone has a 3-D effect on the data in the northern part of the profile. Rotated MT impedances were inverted using a 2-D code. Major resistivity interfaces coincide with the location of the UP-LP shear zone near the surface, and dip towards the Arabian margin suggesting a southwest orientated underthrusting prior to the ophiolite emplacement. The para-autochthonous and less deformed upper plate is a resistor, whereas the strongly deformed lower plate is more conductive.

  9. Three-dimensional inversion for Network-Magnetotelluric data

    NASA Astrophysics Data System (ADS)

    Siripunvaraporn, W.; Uyeshima, M.; Egbert, G.

    2004-09-01

    Three-dimensional inversion of Network-Magnetotelluric (MT) data has been implemented. The program is based on a conventional 3-D MT inversion code (Siripunvaraporn et al., 2004), which is a data space variant of the OCCAM approach. In addition to modifications required for computing Network-MT responses and sensitivities, the program makes use of Massage Passing Interface (MPI) software, with allowing computations for each period to be run on separate CPU nodes. Here, we consider inversion of synthetic data generated from simple models consisting of a 1 W-m conductive block buried at varying depths in a 100 W-m background. We focus in particular on inversion of long period (320-40,960 seconds) data, because Network-MT data usually have high coherency in these period ranges. Even with only long period data the inversion recovers shallow and deep structures, as long as these are large enough to affect the data significantly. However, resolution of the inversion depends greatly on the geometry of the dipole network, the range of periods used, and the horizontal size of the conductive anomaly.

  10. Comparing multiple 3D magnetotelluric inversions of the same dataset

    NASA Astrophysics Data System (ADS)

    Walter, C.; Jones, A. G.

    2013-12-01

    The Taupo Volcanic Zone (TVZ) hosts the majority of the geothermal systems in New Zealand and is a valuable source for power generation and tourism. It is important for the sustainable exploitation of this area to fully understand the processes and structures in the TVZ. As part of the 'Hotter and Deeper' project of the Foundation for Research, Science and Technology (FRST), a dataset of 200 broadband magnetotelluric (MT) stations has been collected in the TVZ of New Zealand in 2009 and 2010. Combined with a smaller dataset from Reporoa, a total of 230 stations are available for 3D inversion to image the deeper structures of the TVZ. For the study presented in this paper, multiple 3D inversions of this dataset using different control parameters have been undertaken to study the influence of the choice of parameters on the inversion result. The parameters that have been varied include; the type of responses used in the inversion, the use of topography and bathymetry, and varying vertical grid spacings. All inversions commenced with a uniform half-space so that there was no preconceived structures to begin with. The results show that the main structures in the model are robust in that they are independent of the choice of parameters and become introduced in every inversion. The only differences are in the shape and exact location of the structures, which vary between the models. Furthermore, different ways to get a measure for the differences between models have been explored.

  11. Magnetotelluric data, Taos Plateau Volcanic Field, New Mexico

    USGS Publications Warehouse

    Ailes, Chad E.; Rodriguez, Brian D.

    2010-01-01

    The population of the San Luis Basin region of northern New Mexico is growing. Water shortfalls could have serious consequences. Future growth and land management in the region depend on accurate assessment and protection of the region's groundwater resources. An important issue in managing the groundwater resources is a better understanding of the hydrogeology of the Santa Fe Group and the nature of the sedimentary deposits that fill the Rio Grande rift, which contain the principal groundwater aquifers. The shallow unconfined aquifer and the deeper confined Santa Fe Group aquifer in the San Luis Basin are the main sources of municipal water for the region. The U.S. Geological Survey (USGS) is conducting a series of multidisciplinary studies of the San Luis Basin. Detailed geologic mapping, high-resolution airborne magnetic surveys, gravity surveys, an electromagnetic survey called magnetotellurics (MT), and hydrologic and lithologic data are being used to better understand the aquifers. This report describes a regional east-west MT sounding profile acquired in late July 2009 across the Taos Plateau Volcanic Field where drillhole data are sparse. Resistivity modeling of the MT data can be used to help map changes in electrical resistivity with depths that are related to differences in rock types. These various rock types help control the properties of aquifers. The purpose of this report is to release the MT sounding data collected along the east-west profile. No interpretation of the data is included.

  12. Magnetotelluric investigation in the High Agri Valley (southern Apennine, Italy)

    NASA Astrophysics Data System (ADS)

    Balasco, M.; Giocoli, A.; Piscitelli, S.; Romano, G.; Siniscalchi, A.; Stabile, T. A.; Tripaldi, S.

    2015-04-01

    In this paper we present the result of a magnetotelluric (MT) investigation carried out across the High Agri Valley (HAV), southern Italy. Several MT soundings were carried out in order to obtain a ~15 km long 2-D resistivity model with an investigation depth of ~10 km. The main aim was to provide valuable data on the geological and structural setting of the HAV. The MT model was compared with pre-existing geological, geophysical and seismic data. The MT model can be schematized as a superposition of three stack lateral varying layers with different thickness and resistivity values: a surficial low-medium resistivity layer associated with the Quaternary deposits and to the allochthonous units; and a deeper high resistivity layer related to the Apulia Platform, separated by a thin layer connected to the mélange zone and to the Pliocene terrigenous marine deposits. Sharp lateral resistivity variations are interpreted as faults that, on the basis of accurate focal mechanism computations, display normal-faulting kinematics.

  13. Magnetotelluric investigation in the High Agri Valley (southern Apennine, Italy)

    NASA Astrophysics Data System (ADS)

    Balasco, M.; Giocoli, A.; Piscitelli, S.; Romano, G.; Siniscalchi, A.; Stabile, T. A.; Tripladi, S.

    2014-11-01

    In this paper we present the result of a Magnetotelluric (MT) investigation carried out across the High Agri Valley (HAV), southern Italy. Several MT soundings were carried out in order to obtain a ~15 km long 2-D resistivity model with an investigation depth of ~10 km. The main aim was to provide valuable data on the geological and structural setting of the HAV. The MT model was compared with pre-existing geological, geophysical and seismic data. The MT model can be schematized as a superposition of three stack lateral varying layers with different thickness and resistivity values: a surficial low-medium resistivity layer, associated to the Quaternary deposits and to the allochthonous units, and a deeper high resistivity layer, related to the Apulia Platform, separated by a thin layer connected to the mélange zone and to the Pliocene terrigenous marine deposits. Sharp lateral resistivity variations are interpreted as faults that, on the basis of accurate focal mechanism computations, display normal-faulting kinematics.

  14. An efficient modified hierarchical domain decomposition for two-dimensional magnetotelluric forward modelling

    NASA Astrophysics Data System (ADS)

    Rung-Arunwan, Tawat; Siripunvaraporn, Weerachai

    2010-11-01

    We use 2-D magnetotelluric (MT) problems as a feasibility study to demonstrate that 3-D MT problems can be solved with a direct solver, even on a standard single processor PC. The scheme used is a hierarchical domain decomposition (HDD) method in which a global computational domain is uniformly split into many smaller non-overlapping subdomains. To make it more efficient, two modifications are made to the standard HDD method. Instead of three levels as in the standard HDD method, we classify the unknowns into four classes: the interiors, the horizontal interfaces, the vertical interfaces and the intersections. Four sets of smaller systems of equations are successively solved with a direct method (an LU factorization). The separation significantly reduces the large memory requirements of a direct solver. It also reduces the CPU time to almost half that of the standard HDD method although it is still slower than the conventional finite difference (FD) method. To further enhance the speed of the code, a red-black ordering is applied to solve the horizontal and vertical interface reduced systems. Numerical experiments on a 2-D MT problem of a given size running on a single processor machine shows that CPU time and memory used are almost constant for any resistivity models, frequencies and modes. This is a clear advantage of our algorithm and is of particular importance if the method is applied to 3-D problems. We show that our new method results in reductions in both memory usage and CPU time for large enough domains when compared to the standard FD and HDD schemes. In addition, we also introduce a `memory minimization map', a graphical tool we can use instead of trial-and-error to pre-select the optimal size of subdomains, which yield the best performance in both CPU time and memory even running on a serial machine.

  15. Magnetotelluric survey to characterize the Sunnyside porphyry copper system in the Patagonia Mountains, Arizona

    USGS Publications Warehouse

    Rodriguez, Brian D.; Sampson, Jay A.

    2010-01-01

    The Sunnyside porphyry copper system is part of the concealed San Rafael Valley porphyry system located in the Patagonia Mountains of Arizona. The U.S. Geological Survey is conducting a series of multidisciplinary studies as part of the Assessment Techniques for Concealed Mineral Resources project. To help characterize the size and resistivity of the mineralized area beneath overburden, a regional east-west magnetotelluric sounding profile was acquired. This is a data release report of the magnetotelluric sounding data collected along the east-west profile; no interpretation of the data is included.

  16. Audio-magnetotelluric survey to characterize the Sunnyside porphyry copper system in the Patagonia Mountains, Arizona

    USGS Publications Warehouse

    Sampson, Jay A.; Rodriguez, Brian D.

    2010-01-01

    The Sunnyside porphyry copper system is part of the concealed San Rafael Valley porphyry system located in the Patagonia Mountains of Arizona. The U.S. Geological Survey is conducting a series of multidisciplinary studies as part of the Assessment Techniques for Concealed Mineral Resources project. To help characterize the size, resistivity, and skin depth of the polarizable mineral deposit concealed beneath thick overburden, a regional east-west audio-magnetotelluric sounding profile was acquired. The purpose of this report is to release the audio-magnetotelluric sounding data collected along that east-west profile. No interpretation of the data is included.

  17. Advances in thermal control and performance of the MMT M1 mirror

    NASA Astrophysics Data System (ADS)

    Gibson, J. D.; Williams, G. G.; Callahan, S.; Comisso, B.; Ortiz, R.; Williams, J. T.

    2010-07-01

    Strategies for thermal control of the 6.5-meter diameter borosilicate honeycomb primary (M1) mirror at the MMT Observatory have included: 1) direct control of ventilation system chiller setpoints by the telescope operator, 2) semiautomated control of chiller setpoints, using a fixed offset from the ambient temperature, and 3) most recently, an automated temperature controller for conditioned air. Details of this automated controller, including the integration of multiple chillers, heat exchangers, and temperature/dew point sensors, are presented here. Constraints and sanity checks for thermal control are also discussed, including: 1) mirror and hardware safety, 2) aluminum coating preservation, and 3) optimization of M1 thermal conditions for science acquisition by minimizing both air-to-glass temperature differences, which cause mirror seeing, and internal glass temperature gradients, which cause wavefront errors. Consideration is given to special operating conditions, such as high dew and frost points. Precise temperature control of conditioned ventilation air as delivered to the M1 mirror cell is also discussed. The performance of the new automated controller is assessed and compared to previous control strategies. Finally, suggestions are made for further refinement of the M1 mirror thermal control system and related algorithms.

  18. Status of the 6.5m MMT Telescope laser adaptive optics system

    NASA Astrophysics Data System (ADS)

    Bendek, Eduardo A.; Hart, Michael; Powell, Keith B.; Milton, Norman M.; Vaitheeswaran, Vidhya; McCarthy, Don; Kulesa, Craig; Callahan, Shawn; Ammons, S. Mark; Garcia Rissmann, Aurea

    2010-07-01

    The Laser Adaptive Optics system of the 6.5 m MMT telescope has now been commissioned with Ground Layer Adaptive Optics operations as a tool for astronomical science. In this mode the wavefronts sampled by each of five laser beacons are averaged, leading to an estimate of the aberration in the ground layer. The ground layer is then compensated by the deformable secondary mirror at 400 Hz. Image quality of 0.2-0.3 arc sec is delivered in the near infrared bands from 1.2-2.5 μm over a field of view of 2 arc minutes. Tomographic wavefront sensing tests in May 2010 produced open loop data necessary to streamline the software to generate a Laser Tomography Adaptive Optics (LTAO) reconstructor. In addition, we present the work being done to achieve optimal control PID wavefront control and thus increase the disturbance rejection frequency response for the system. Finally, we briefly describe plans to mount the ARIES near infrared imager and echelle spectrograph, which will support the 2 arc min ground-layer corrected field and will exploit the diffraction limit anticipated with LTAO.

  19. Synthesis of novel MMT/acyl-protected nucleo alanine monomers for the preparation of DNA/alanyl-PNA chimeras

    PubMed Central

    Roviello, G. N.; Gröschel, S.; Pedone, C.

    2009-01-01

    Alanyl-peptide nucleic acid (alanyl-PNA)/DNA chimeras are oligomers envisaged to be beneficial in efficient DNA diagnostics based on an improved molecular beacon concept. A synthesis of alanyl-PNA/DNA chimera can be based on the solid phase assembly of the oligomer with mixed oligonucleotide/peptide backbone under DNA synthesis conditions, in which the nucleotides are introduced as phosphoramidites, whereas the nucleo amino acids make use of the acid labile monomethoxytrityl (MMT) group for temporary protection of the α-amino groups and acyl protecting groups for the exocyclic amino functions of the nucleobases. In this work, we realized for the first time the synthesis of all four MMT/acyl-protected nucleo alanines, achieved by deprotection/reprotection of the newly synthesized Boc/acyl intermediates, useful monomers for the obtainment of (alanyl-PNA)/DNA chimeras by conditions fully compatible with the standard phosphoramidite DNA synthesis strategy. PMID:19629638

  20. Update on a Pharmacokinetic-Centric Alternative Tier II Program for MMT-Part I: Program Implementation and Lessons Learned.

    PubMed

    Dorman, David C; Andersen, Melvin E; Roper, Jerry M; Taylor, Michael D

    2012-01-01

    Concerns have been raised regarding environmental manganese exposure since high exposures have been associated with neurological disorders. The USA Environmental Protection Agency most recent human health risk assessment of inhaled manganese conducted in 1993 identified specific areas of uncertainty regarding manganese pharmacokinetics. This led to the development of a test rule under the USA Clean Air Act that required the generation of pharmacokinetic information on the inorganic manganese combustion products of the organometallic fuel additive methylcyclopentadienyl manganese tricarbonyl (MMT). The Alternative Tier 2 testing program for MMT, described in this paper, has yielded substantial pharmacokinetic data and has enabled the generation of physiologically based pharmacokinetic (PBPK) models for manganese. These models are capable of predicting tissue manganese concentrations across a variety of dose routes, levels, and durations while accounting for factors such as age, gender, and reproductive status, enabling the consideration of tissue dosimetry in future risk assessments. PMID:22545047

  1. Multiscale joint interpretation of seismic and magnetotelluric data in Hontomín (Spain): From shallow subsurface to reservoir.

    NASA Astrophysics Data System (ADS)

    Ogaya, Xènia; Alcalde, Juan; Marzán, Ignacio; Ledo, Juanjo; Queralt, Pilar; Marcuello, Alex; Saura, Eduard; Martí, David; Carbonell, Ramón; Benjumea, Beatriz

    2016-04-01

    The village of Hontomín (north of Spain) hosts the first Technological Development Plant (TDP) for CO2 geological storage located in Spain. The study area has been extensively surveyed to produce a multidisciplinary characterisation, including a 36 km2 3D seismic survey and a circumscribed 15 km2 3D magnetotelluric (MT) survey. In this work, we use the outcomes of these two methods to produce a combined characterisation of the subsurface of Hontomín. This characterisation is carried out at three different scales: reservoir, borehole and shallow subsurface. (1) At reservoir scale, characterisation is obtained by comparing the 3D structural model, obtained from the interpretation of the seismic dataset, with the resistivity model obtained from the 3D MT survey. This joint interpretation highlights the similarities and disagreements between the two models, which informs of their good complementarity. (2) At borehole scale, there is an outstanding correlation between the resistivity logs and the resistivity model obtained by the inversion of the 3D MT data. This allowed building resistivity-velocity pairs from the wireline-log data across the entire sedimentary sequence with confidence, and furthermore computing resistivity-velocity relationships for each formation. These relationships are used to calculate a 3D velocity model from the resistivity model. The agreement between the two velocity models is evaluated at the target depth (reservoir and seal formations). (3) At shallow subsurface (40 m depth), the derived velocity model is compared to the inverted model used in the static correction calculations in the seismic data. The results allowed extracting information about the characteristics of the shallow sediments, suggesting geometry and location of potential karstic structures present in the study area. This work explores the compatibility of the seismic and magnetotelluric methods across scales highlighting the importance of joint interpretation in

  2. Magnetotelluric Investigation of Melt Storage Beneath Okmok Caldera, Alaska

    NASA Astrophysics Data System (ADS)

    Bennington, N. L.; Bedrosian, P.; Key, K.; Zelenak, G.

    2015-12-01

    Alaska accounts for nearly 99% of the seismic moment release within the US. Much of this is associated with the Aleutian volcanic arc, the most tectonically active region in North America, and an ideal location for studying arc magmatism. Okmok is an active volcano located in the central Aleutian arc, defined by a pair of nested, 10 km diameter calderas. The subdued topography of Okmok, relative to other Aleutian volcanoes, improves access and permits dense sampling within the caldera closer to the underlying magmatic system. Okmok volcano was selected as the site of study for this project due to frequent volcanic activity and the presence of a crustal magma reservoir as inferred from previous coarse resolution seismic studies. In June-July 2015, we carried out an amphibious geophysical field deployment at Okmok. Onshore work in and around the volcano included collection of an array of magnetotelluric (MT) stations and installation of a temporary, year-long seismic array. A ring of 3D offshore MT deployments made around the island augments the onshore array. An additional 2D tectonic-scale profile spans the trench, volcanic arc, and backarc. This new geophysical data will be used to gain a greater understanding of Aleutian arc melt generation, migration, and storage beneath an active caldera. We present results from the analysis of the newly collected amphibious 3D MT data. This data will be used to model the distribution and migration of melt within Okmok's crustal magma reservoir. Initial processing of the data shows strong MT signal levels, in particular from a geomagnetic storm that occurred from June 21-23, 2015. A companion abstract discussing the 2D tectonic scale MT profile, which constrains the mantle and deep crust beneath Okmok volcano, is discussed by Zelenak et al.

  3. Dimensionality and geological implications of a sparse magnetotelluric dataset

    NASA Astrophysics Data System (ADS)

    Derosier, B.; Dennis, K. N.; Plata Martinez, R. O.; Montahaei, M.; Bedrosian, P.; Pellerin, L.

    2014-12-01

    High-quality broadband magnetotelluric (MT) data (0.01-1000 s period) were acquired at four stations in Borrego Canyon within the Santo Domingo Basin of the Rio Grande Rift, New Mexico, during the 2014 Summer of Applied Geophysical Experience (SAGE) field program. MT response functions along the 10-km long NW trending profile are nearly identical with all stations showing a distinct mode split at 10 s period, suggesting a significant conductivity contrast is located roughly 10-20 km away from the profile based on skin depth estimates. Audiomagnetotelluric, polar diagrams, impedance skew, induction vectors and phase tensor analysis all indicate one-dimensional (1-D) structure at periods <10 sec, a predominantly two-dimensional (2-D) structure at intermediate depths (10-100 s) with a 60° geoelectric strike, and three-dimensional (3-D) structure at the longest periods. Inverse modeling of the data from 0.01-10 s reveals a three-layer electrical structure: a moderately resistive sediments from the surface to ~750 m depth, a conductive layer (weathered volcanoclastics) to 4 km depth, and below 4 km a highly resistive basement of Mesozoic and Precambrian rocks. A 2-D inverse model converged, but resulted in physically unrealistic structure. Hence a 3-D forward model study was performed using the 2014 data together with three additional MT stations acquired further to the east during SAGE 2010. Models that include a NE-trending conductive structure to the north of the profile show broad consistency between the measured and synthetic phase tensors and impedances. We infer our MT data to be on the conductive side of this contact, with the resistive material to the NW attributed to a heavily intruded crust beneath the Jemez lineament, and possibly the edge of the thick lithosphere beneath the Colorado Plateau. 3-D inversion of this sparse data set is being carried out to determine whether this conceptual model is consistent with the full impedance tensor and tipper data.

  4. Two-dimensional magnetotelluric inversion of the EMSLAB Lincoln Line

    NASA Astrophysics Data System (ADS)

    Jiracek, George R.; Curtis, Jeffrey H.; Ramirez, Jorge; Martinez, Mario; Romo, Jose

    1989-10-01

    Two-dimensional, Backus-Gilbert inversion of the EMSLAB land magnetotelluric (MT) data along the 200-km-long Lincoln Line has yielded optimally smooth geoelectric sections. Inversions were performed on the apparent resistivity and impedance phase data approximating the transverse magnetic (TM) mode. The land portion of the Lincoln Line traverses the edge of the North American plate that is being underthrust by the Juan de Fuca plate system. The inversion reveals three centralized conductive zones in the depth range of 20-40 km. A slightly conducting (<100 S) zone is centered at 30-35 km depth under the Oregon Coast Range; this feature may be the top of the subducting Juan de Fuca plate since there is complementary evidence here from Consortium for Continental Reflection Profiling seismic data. A prominent conduction zone of several hundred Siemens (S) is also detected at 30-35 km depth under the very resistive (>1000 ohm m) Western Cascades. Here the depth is too shallow for the zone to be the subducting plate. There is also evidence for a highly conducting (>1000 S) lower crust east of the High Cascades on the east end of the Lincoln Line. Two vertical conductive regions are also exposed in the inversion model. One occurs at 70-80 km from the coast under the Willamette Valley where a postulated Eocene trench may have left a suture zone. The second region is coincident with surface hydrothermal activity along the Western-High Cascades boundary. There are ample sources of water in the crust, e.g., in subducted sediments, from dehydration reactions along the upper plate boundary, and in volcanic arc magmas, to lead us to believe that hot, saline water is the major source of the conductive occurrences along the Lincoln Line. However, the various zones appear to be distinct, and the water may be trapped by different mechanisms.

  5. Subsurface resistivity images of the Belik area, Purbalingga based on magnetotelluric data, implication for hydrocarbon exploration

    NASA Astrophysics Data System (ADS)

    Gaffar, Eddy Z.

    2016-02-01

    The study area is an area of hydrocarbon potential located in Belik Area, Central Java. From the results of seismic survey, it seen that the depth of about 2000 meters is still visible, but the signal of the seismic instrument could not penetrate deeper than 2000 meters. Therefore, Research Center for Geotechnology did an alternative method of magnetoteluric with trending north-south trajectory. Based on Djuri 1996, the stratigraphy of the study area consists of Tertiary to the Quaternary rocks. From the oldest is Pemali Formation, Rambatan Formation, Halang Formation, Kumbang Formation, Tapak Formation, Kalibiuk Formation, Ligung Formation and Alluvial. Pemali Formation consists of marl, Rambatan Formation consists of shale, marl and calcareous sandstone, Halang Formation consists of sandstone, conglomerate and marl, Kumbang Formation consists of breccia, andesite lava and tuff, Tapak Formation consists of breccia and limestone, Kalibiuk Formation consists of silty marl and sandstone Ligung Formation consists of agglomerates, breccias, tuffs and clays. Kumbang Formation is an igneous rock as sill with a thickness of up to 2000 meters and is a breakthrough that layered rocks parallel to the rock above and below. Resistivity image of the north-south trajectory is seen a layer with high resistivity more than 1000 OhmM. It is interpreted as Kumbang Formation and underneath there is a layer with resistivity values lower than Kumbang Formation is interpreted as Halang Formation, Rambatan Formation and Pemali Formation. It is concluded that magnetotelluric method could penetrate very high resistivity layer and thick enough where seismic method can not penetrate.

  6. MT+, integrating magnetotellurics to determine earth structure, physical state, and processes

    USGS Publications Warehouse

    Bedrosian, P.A.

    2007-01-01

    As one of the few deep-earth imaging techniques, magnetotellurics provides information on both the structure and physical state of the crust and upper mantle. Magnetotellurics is sensitive to electrical conductivity, which varies within the earth by many orders of magnitude and is modified by a range of earth processes. As with all geophysical techniques, magnetotellurics has a non-unique inverse problem and has limitations in resolution and sensitivity. As such, an integrated approach, either via the joint interpretation of independent geophysical models, or through the simultaneous inversion of independent data sets is valuable, and at times essential to an accurate interpretation. Magnetotelluric data and models are increasingly integrated with geological, geophysical and geochemical information. This review considers recent studies that illustrate the ways in which such information is combined, from qualitative comparisons to statistical correlation studies to multi-property inversions. Also emphasized are the range of problems addressed by these integrated approaches, and their value in elucidating earth structure, physical state, and processes. ?? Springer Science+Business Media B.V. 2007.

  7. Using seismically constrained magnetotelluric inversion to recover velocity structure in the shallow lithosphere

    NASA Astrophysics Data System (ADS)

    Moorkamp, M.; Fishwick, S.; Jones, A. G.

    2015-12-01

    Typical surface wave tomography can recover well the velocity structure of the upper mantle in the depth range between 70-200km. For a successful inversion, we have to constrain the crustal structure and assess the impact on the resulting models. In addition,we often observe potentially interesting features in the uppermost lithosphere which are poorly resolved and thus their interpretationhas to be approached with great care.We are currently developing a seismically constrained magnetotelluric (MT) inversion approach with the aim of better recovering the lithospheric properties (and thus seismic velocities) in these problematic areas. We perform a 3D MT inversion constrained by a fixed seismic velocity model from surface wave tomography. In order to avoid strong bias, we only utilize information on structural boundaries to combine these two methods. Within the region that is well resolved by both methods, we can then extract a velocity-conductivity relationship. By translating the conductivitiesretrieved from MT into velocities in areas where the velocity model is poorly resolved, we can generate an updated velocity model and test what impactthe updated velocities have on the predicted data.We test this new approach using a MT dataset acquired in central Botswana over the Okwa terrane and the adjacent Kaapvaal and Zimbabwe Cratons togetherwith a tomographic models for the region. Here, both datasets have previously been used to constrain lithospheric structure and show some similarities.We carefully asses the validity of our results by comparing with observations and petrophysical predictions for the conductivity-velocity relationship.

  8. Trans-dimensional Monte Carlo sampling applied to the magnetotelluric inverse problem

    NASA Astrophysics Data System (ADS)

    Mandolesi, Eric; Piana Agostinetti, Nicola

    2015-01-01

    The data required to build geological models of the subsurface are often unavailable from direct measurements or well logs. In order to image the subsurface geological structures several geophysical methods have been developed. The magnetotelluric (MT) method uses natural, time-varying electromagnetic (EM) fields as its source to measure the EM impedance of the subsurface. The interpretation of these data is routinely undertaken by solving inverse problems to produce 1D, 2D or 3D electrical conductivity models of the subsurface. In classical MT inverse problems the investigated models are parametrized using a fixed number of unknowns (i.e. fixed number of layers in a 1D model, or a fixed number of cells in a 2D model), and the non-uniqueness of the solution is handled by a regularization term added to the objective function. This study presents a different approach to the 1D MT inverse problem, by using a trans-dimensional Monte Carlo sampling algorithm, where trans-dimensionality implies that the number of unknown parameters is a parameter itself. This construction has been shown to have a built-in Occam razor, so that the regularization term is not required to produce a simple model. The influences of subjective choices in the interpretation process can therefore be sensibly reduced. The inverse problem is solved within a Bayesian framework, where posterior probability distribution of the investigated parameters are sought, rather than a single best-fit model, and uncertainties on the model parameters, and their correlation, can be easily measured.

  9. Broadband signal generator for the approximation of a magnetotelluric source for indoor testing

    NASA Astrophysics Data System (ADS)

    Ge, Shuang-chao; Deng, Ming; Chen, Kai; Shi, Xin-yu

    2016-08-01

    To test the frequency response of a magnetotelluric (MT) receiver, a broadband source, especially white noise is more efficient and intuitive than single frequency signals. In view of the absence of an appropriate source generator for MT receiver indoor testing, we designed a broadband signal generator based on a pseudo-random binary sequence (PRBS). Firstly, we divided the whole MT band into two segments to avoid data redundancy and simplify calculation in data processing and designed a generator composed of several modules: a clock module, a PRBS logic module, and a voltage level conversion module. We conducted a detailed analysis of the optimal parameter selection methods for each module, and key parameters including clock frequency, order, the primitive polynomial and the original states of the linear registers were determined. The generator provides four-channel PRBS signals with two effective bandwidths of 5  ×  10‑4–714 Hz and 0.1 Hz–14 kHz which are broad enough to cover the frequency range for different MT methods. These four-channel signals were used to simulate two modes of sources (xy and yx) with strong auto-correlation and weak cross-correlation. The power spectral density is quite stable in the whole passband. The new generator is characterized by broadband output in low-frequency bands, low power consumption, simple operation and reliable performance. Indoor and field tests indicated that the generator can provide an analog MT source and is a practical tool for MT receiver indoor testing.

  10. Imaging the conductivity anomalies at the vicinity of Ganos Fault, northwest Turkey by magnetotellurics

    NASA Astrophysics Data System (ADS)

    Karaş, Mustafa; Tank, Bülent; Özaydın, Sinan

    2016-04-01

    Audio-frequency magnetotelluric (AMT: 10400 Hz. - 1 Hz.) data were collected across Ganos Fault, near Mürefte, at the western part of North Anatolian Fault, Turkey. The twelve observation points were densely distributed to form a north - south aligned continuous profile that aims to reveal the electrical resisitivity structure to a depth of 1500 m. Ganos Fault is inactive since 1912 Mürefte Earthquake (Ms: 7.4) and acts as a locked segment with the potential to generate a significant event in the near future. Preliminary dimensionality analyses of the AMT data were performed by using three approaches; strike angle determination following Groom and Bailey decomposition (N70°E), phase tensor analyses (N70°E) and induction vectors (N60°E). All of these methods gave results that are in good agreement with present geological (N70°E) and seismological (N70°E) values. Following the dimensionality analyses, two- and three- dimensional numerical modeling routines were utilized to perform inverse modeling. The inversions were performed by different methods such as Rodi and Mackie, WinGLink, (2001) and Ogawa and Uchida, ABIC, (1996) for 2D and Siripunvaraporn et al., WSINV3DMT (2005) and Egbert and Kelbert, ModEM (2012) for 3D. All modeling attempts ended up with similar models suggesting that: (i) A significant low resistivity anomaly was detected just below the fault's trace representing the so-called "fault zone conductor" with 400 m width and 500 m depth, (ii) An asymmetric damage zone is present involving the fault's core concentrated to the south, (iii) A resistivity contrast between the two sides of the fault, representing a geological boundary between Eocene aged Keşan Formation in the north and Miocene aged Çengelli Formation in the south (iv) Opiholitic basement appears as a high resistivity block at a depth of 800 m.

  11. Pattern recognition and lithological interpretation of collocated seismic and magnetotelluric models using self-organizing maps

    NASA Astrophysics Data System (ADS)

    Bauer, K.; Muñoz, G.; Moeck, I.

    2012-05-01

    Joint interpretation of models from seismic tomography and inversion of magnetotelluric (MT) data is an efficient approach to determine the lithology of the subsurface. Statistical methods are well established but were developed for only two types of models so far (seismic P velocity and electrical resistivity). We apply self-organizing maps (SOMs), which have no limitations in the number of parameters considered in the joint interpretation. Our SOM method includes (1) generation of data vectors from the seismic and MT images, (2) unsupervised learning, (3) definition of classes by algorithmic segmentation of the SOM using image processing techniques and (4) application of learned knowledge to classify all data vectors and assign a lithological interpretation for each data vector. We apply the workflow to collocated P velocity, vertical P-velocity gradient and resistivity models derived along a 40 km profile around the geothermal site Groß Schönebeck in the Northeast German Basin. The resulting lithological model consists of eight classes covering Cenozoic, Mesozoic and Palaeozoic sediments down to 5 km depth. There is a remarkable agreement between the litho-type distribution from the SOM analysis and regional marker horizons interpolated from sparse 2-D industrial reflection seismic data. The most interesting features include (1) characteristic properties of the Jurassic (low P-velocity gradients, low resistivity values) interpreted as the signature of shales, and (2) a pattern within the Upper Permian Zechstein layer with low resistivity and increased P-velocity values within the salt depressions and increased resistivity and decreased P velocities in the salt pillows. The latter is explained in our interpretation by flow of less dense salt matrix components to form the pillows while denser and more brittle evaporites such as anhydrite remain in place during the salt mobilization.

  12. Shallow water radio-magnetotelluric (RMT) measurements in urban environment: A case study from Stockholm city

    NASA Astrophysics Data System (ADS)

    Mehta, Suman; Bastani, Mehrdad; Malehmir, Alireza; Wang, Shunguo; Pedersen, Laust

    2014-05-01

    of the impedance tensor were obtained by the parametric representation combined with a Truncated Singular Value Decomposition (TSVD) regularization of Bastani and Pedersen (2001). The processed data were then inverted to obtain 2D resistivity models. The resulting models along 23 lines correlate well and image variation of water depth, thickness of subaqueous sediments as well as the depth to crystalline bedrock. Low resistivity zones observed in the bedrock coincide well with the low velocity zones identified in refraction seismic surveys available along the RMT lines, indicating the presence of possible fracture zones in the bedrock. The experiment illustrates that the RMT methods can be well adapted to this type of environment; it is fast and cost-effective in shallow water especially in urban settings. Acknowledgments: Formas, SGU, BeFo, SBUF, Skanska, Boliden, FQM and NGI References: Bastani, M., 2001, EnviroMT - a new Controlled Source/Radio Magnetotelluric System: Ph.D. thesis, ISBN 91-554-5051-2, Uppsala University. Bastani, M. and Pedersen, L. B., 2001, Estimation of magnetotelluric transfer functions from radio transmitters. GEOPHYSICS, 66, 1038-1051.

  13. Magnetotelluric data, stable distributions and impropriety: an existential combination

    NASA Astrophysics Data System (ADS)

    Chave, Alan D.

    2014-07-01

    The robust statistical model of a Gaussian core contaminated by outlying data that underlies robust estimation of the magnetotelluric (MT) response function has been re-examined. The residuals from robust estimators are systematically long tailed compared to a distribution based on the Gaussian, and hence are inconsistent with the robust model. Instead, MT data are pervasively described by the alpha stable distribution family whose variance and sometimes mean are undefined. A maximum likelihood estimator (MLE) that exploits the stable nature of MT data is formulated, and its two-stage implementation in which stable parameters are first fit to the data and then the MT responses are solved for is described. The MLE is shown to be inherently robust, but differs from the conventional robust estimator because it is based on a model derived from the data, while robust estimators are ad hoc, being based on the robust model that is inconsistent with actual data. Propriety versus impropriety of the complex MT response was investigated, and a likelihood ratio test for propriety and its null distribution was established. The Cramér-Rao lower bounds for the covariance matrix of proper and improper MT responses were specified. The MLE was applied to exemplar long period and broad-band data sets from South Africa. Both are shown to be significantly stably distributed using the Kolmogorov-Smirnov goodness of fit and Ansari-Bradley non-parametric dispersion tests. Impropriety of the MT responses at both sites is pervasive, hence the improper Cramér-Rao bound was used to estimate the MLE covariance. The MLE is shown to be nearly unbiased and well described by a Gaussian distribution based on bootstrap simulation. The MLE was compared to a conventional robust estimator, establishing that the standard errors of the former are systematically smaller than for the latter and that the standardized differences between them exhibit excursions that are both too frequent and too large to

  14. Crustal Scale Magnetotelluric Imaging of the Central Atlas in Moocco

    NASA Astrophysics Data System (ADS)

    Ledo, J.; Jones, A. G.; Sinischalchi, A.; Rouais, M.; Campanyà, J.; Kiyan, D.; Moretti, P.; Piña, P.; Hogg, C.; Romano, G.; Picasso Team

    2010-12-01

    The Central Atlas of Morocco is an intracontinental fold-thrust belt with an ENE-WSW main strike that extends about 2000 km and 100 km wide, located in the foreland of the Mediterranean Alpine belt. The structure of the Atlas resulted from the tectonic inversion of a Mesozoic extensional basin, due to compression related to convergence between Africa and Europe occurred from cenozoic to present times. Previous MT data models based on stitched 1D inversion or using only the phases and the induction vector data following and trial and error approach (Schwarz et al., 1992), therefore the overall geoelectrical structure is partly unresolved. In this paper we will expose and discuss the results of new magnetotelluric data acquired along a profile crossing the Atlas that allows imaging its electrical crustal structure.In the lower crust two conductive units appear. One below the Moulouya plains that coincides with a minimum of the Bouguer anomaly, less earthquakes than the adjacent Middle and High Atlas and a low velocity anomaly at lower crustal levels. Moreover, the Moulouya plain and the Middle Atlas to the north are host of the largest Neogene-Quaternary intraplate alkaline volcanic field in Morocco. This feature has been associated either to a Canary mantle plume flow beneath Africa or to the interplay between reactivation of inherited geological structures and the thermal erosion of the metasomatized lithosphere. In any case, all the authors agree that are originated by low degree partial melting of sublithospheric mantle sources. Another low resistivity anomaly appears at lower crustal depths below the Anti-Atlas, that could be either a remnant of tectonic processes in the pre-mesozoic or a more recent overprint of the lower crust due to mantle processes. Two main events during the Pan African orogeny may be the cause of this anomaly, a relic of a subduction process or a deep mineralization associated to magmatism. The Anti-Atlas consists of of a Precambrian

  15. The Amplitude Phase Decomposition for the Magnetotelluric Impedance Tensor and Galvanic Electric Distortion

    NASA Astrophysics Data System (ADS)

    Neukirch, Maik; Rudolf, Daniel; Garcia, Xavier

    2016-04-01

    The introduction of the phase tensor marked a major breakthrough in understanding of, analysing of and dealing with galvanic distortion of the electric field in the Magnetotelluric method. The phase tensor itself can be used for (distortion free) dimensionality analysis, if applicable distortion analysis and even to invert for subsurface models. However, impedance amplitude information is not stored in the phase tensor, therefore the impedance corrected by distortion analysis (or alternative remedies) may yield better results. We formulate an impedance tensor decomposition into the known phase tensor and an amplitude tensor that is shown to be complementary and independent of the phase tensor. The rotational invariant amplitude tensor contains galvanic and inductive amplitudes of which the latter are physically related to the inductive phase information present in the phase tensor. We show, that for the special cases of 1D and 2D subsurfaces, the geometric amplitude tensor parameter (strike and skew) converge to phase tensor parameter and the singular values are the amplitudes of the impedance in TE and TM mode. Further, the physical similarity between inductive phase and amplitude is used to approximate the galvanic amplitude for the general subsurface, which leads to the qualitative interpretation of 3D galvanic distortion: (i) the (purely) galvanic part of the subsurface (as sensed at a given period) may have a changing impact on the impedance (over a period range) and (ii) only the purely galvanic response of the lowest available period should be termed galvanic distortion. The approximation of the galvanic amplitude (and therewith galvanic distortion), though not accurate, offers a new perspective on galvanic distortion, which breaks with the general belief of the need to assume 1D or 2D regional structure for the impedance. The amplitude tensor itself is complementary to the phase tensor containing integrated (galvanic and inductive) subsurface information

  16. Processing of noisy magnetotelluric data using digital filters and additional data selection criteria

    NASA Astrophysics Data System (ADS)

    Fontes, S. L.; Harinarayana, T.; Dawes, G. J. K.; Hutton, V. R. S.

    1988-10-01

    Although the magnetotelluric (MT) method is known to be effective and fast in probing the electrical conductivity structure of the Earth at crustal depths, the results are often degraded by industrial and cultural noise. To obtain reliable processed results for modelling, it is first necessary to extract or select the natural signals from the contaminated time series. Various noise-reduction techniques based on digital filters are discussed with special reference to persistent noise signals, e.g. from power lines, DC-operated railways and electrical fences. Both previously suggested techniques (delay-line and notch filtering) and two other procedures (maximum entropy extension and deconvolution filtering) are applied to both synthetic data and to field observations from southern Scotland and the Italian Alps. Better quality data sets and more geophysically acceptable Earth models are shown to result. Noise of a more intermittent nature has recently been observed in MT observations near the development site of the geothermal power station on Milos, Greece. Large highly coherent electromagnetic field signals were observed to coincide with the opening and closure of the valves on the test wells. In this case, meaningful apparent resistivity curves could be obtained from an undisturbed subset of the previously accepted data, which had been selected mainly on the basis of signal power. Delay-line filtering is shown to be superior to notch filtering in eliminating non-sinusoidal noise, while both the MEM extension and the window deconvolution techniques are found to be useful in spike removal. These studies illustrate that use of an automatic data selection procedure should only be undertaken with great care in areas where the cultural noise is high. In such cases, continuous time-domain monitoring of the MT signals is recommended. The appropriate techniques of noise reduction can then be applied.

  17. A magnetotelluric study of the sensitivity of an area to seismoelectric signals

    USGS Publications Warehouse

    Balasis, G.; Bedrosian, P.A.; Eftaxias, K.

    2005-01-01

    During recent years, efforts at better understanding the physical properties of precursory ultra-low frequency pre-seismic electric signals (SES) have been intensified. Experiments show that SES cannot be observed at all points of the Earth's surface but only at certain so-called sensitive sites. Moreover, a sensitive site is capable of collecting SES from only a restricted number of seismic areas (selectivity effect). Tberefore the installation of a permanent station appropriate for SES collection should necessarily be preceded by a pilot study over a broad area and for a long duration. In short, a number of temporary stations are installed and, after the occurrence of several significant earthquakes (EQs) from a given seismic area, the most appropriate (if any) of these temporary stations, in the sense that they happen to collect SES, can be selected as permanent. Such a long experiment constitutes a serious disadvantage in identifying a site as SES sensitive. However, the SES sensitivity of a site should be related to the geoelectric structure of the area that hosts the site as well as the regional geoelectric structure between the station and the seismic focal area. Thus, knowledge of the local and regional geoelectric structure can dramatically reduce the time involved in identifying SES sites. hi this paper the magnetotelluric method is used to investigate the conductivity structure of an area where a permanent SES station is in operation. Although general conclusions cannot be drawn, the area surrounding an SES site near Ioannina, Greece is characterized by: (1) major faults in the vicinity; (2) highly resistive structure flanked by abrupt conductivity contrasts associated with large-scale geologic contacts, and (3) local inhomogeneities in conductivity structure. The above results are consistent with the fact that electric field amplitudes from remotely-generated signals should be appreciably stronger at such sites when compared to neighboring sites

  18. The impact of ultra-low amounts of amino-modified MMT on dynamics and properties of densely cross-linked cyanate ester resins

    NASA Astrophysics Data System (ADS)

    Bershtein, Vladimir; Fainleib, Alexander; Egorova, Larisa; Gusakova, Kristina; Grigoryeva, Olga; Kirilenko, Demid; Konnikov, Semen; Ryzhov, Valery; Yakushev, Pavel; Lavrenyuk, Natalia

    2015-04-01

    Thermostable nanocomposites based on densely cross-linked cyanate ester resins (CER), derived from bisphenol E and doped by 0.01 to 5 wt. % amino-functionalized 2D montmorillonite (MMT) nanoparticles, were synthesized and characterized using Fourier transform infrared (FTIR), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDXS), wide-angle X-ray diffraction (WAXD), dynamic mechanical analysis (DMA), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), far-infrared (Far-IR), and creep rate spectroscopy (CRS) techniques. It was revealed that ultra-low additives, e.g., 0.025 to 0.1 wt. %, of amino-MMT nanolayers covalently embedded into CER network exerted an anomalously large impact on its dynamics and properties resulting, in particular, in some suppression of dynamics, increasing the onset of glass transition temperature by 30° to 40° and twofold rise of modulus in temperature range from 20°C to 200°C. Contrarily, the effects became negligibly small or even negative at increased amino-MMT contents, especially at 2 and 5 wt. %. That could be explained by TEM/EDXS data displaying predominance of individual amino-MMT nanolayers and their thin (2 to 3 nanolayers) stacks over more thick tactoids (5 to 10 nanolayers) and the large amino-MMT aggregates (100 to 500 nm in thickness) reversing the composite structure produced with increasing of amino-MMT content within CER matrix. The revealed effect of ultra-low amino-MMT content testifies in favor of the idea about the extraordinarily enhanced long-range action of the `constrained dynamics' effect in the case of densely cross-linked polymer networks.

  19. Calibration and testing of the 6.5 m MMT adaptive optics system

    NASA Astrophysics Data System (ADS)

    Johnson, Robert Lee

    2001-10-01

    This dissertation describes the development, calibration, and testing of the adaptive optics system for the 6.5 m Multiple Mirror Telescope. By employing a deformable secondary mirror, the MMT adaptive optics system uniquely solves several problems typical of astronomical adaptive optics systems. Extra components are eliminated, improving throughput and reducing emissivity. Since the adaptive secondary is integral to the telescope, a corrected beam is presented to any instrument mounted at Cassegrain focus. The testing of an adaptive mirror, which is large and convex, poses a new and difficult problem. I present a test apparatus that allows complete calibration and operation, in closed-loop, of the entire adaptive optics system in the laboratory. The test apparatus replicates the optical path of the telescope with a wavefront error of less than 500 nm RMS. To simulate atmospheric turbulence, machined acrylic plates are included. A phase-shifting interferometer allows calibration of the Shack-Hartmann wavefront sensor and reconstruction algorithms; comparisons agree to one-third of the root-mean-square wavefront. First, techniques were developed to align the apparatus and measure residual aberration. Then, the wavefront sensor was calibrated by measuring its response to introduced tilt. Lastly, a Fourier wave-optics approach was used to produce a modal wavefront reconstructor. The adaptive secondary mirror uses electro-magnetic force actuators. Capacitive position sensors are placed at each actuator to permit control of the mirror shape without measuring the reflected wavefront. These sensors have nanometer resolution, but require calibration. To calibrate the sensors, I developed a small optical instrument which measures the thickness of transparent films to an absolute accuracy of 5 nm with a precision of 2 nm. The device has applications far beyond the scope of this research. Twenty-four of these optical gap sensors have been built to calibrate the 336 capacitive

  20. High resolution imaging of the Methana volcanic complex, Greece, with magnetotelluric and aeromagnetic data

    NASA Astrophysics Data System (ADS)

    Efstathiou, A.; Tzanis, A.; Chailas, S.; Lagios, E.; Stamatakis, M.

    2012-04-01

    The Methana calc-alkaline volcanic complex is located off the NE coast of Argolis Peninsula (Peloponnesus, Greece) at the NW terminus of the Hellenic Volcanic Arc (HVA). It consists of approximately 32 domes, with the most recent eruptive episodes dated to 258 BCE and 1700 CE. Herein, we report the results an attempt to investigate the volcano's interior with joint interpretation of Magnetotelluric and Aeromagnetic data. The aeromagnetic data was inverted with the UBC-GIF 3D magnetic inversion suite, constrained by several in-situ susceptibility measurements. At depths to 2 km, the inversion resolves individual intrusions corresponding to known phases of volcanic activity (domes), with susceptibilities >0.1. At depths greater than 4.5 km, a more weakly magnetized domain is detected (~0.025); its ceiling is well resolved; its floor cannot be placed with certainty but extends to at least 7 km. The depths are comparable to those of magma chambers. Based on the palaeomagnetic analysis of nearby volcanic rocks, it may be safely suggested that its temperature should not be higher than 550-600°C, but also not considerably lower. It may comprise a magma chamber, inasmuch as it compares well with the temperatures and locations of known magma chambers along the HVA. Finally, there's exists evidence of the location of the vents through which the extrusive activity has taken place. A Magnetotelluric survey comprising 14 stations was conducted IN 1992, as part of a geothermal project. Herein, this data is reevaluated with modern analysis methods and re-interpreted with 2D inversion. The results indicate the presence of conductors at depths of 1500-2500 m beneath the centre of the Peninsula, extensive horizontal conductors at, or just below sea level and conductive protrusions above sea level. The joint interpretation of the susceptibility and geoelectric images is based on the premise that they both are generated by hydrothermal circulation which depresses resistivity and

  1. Effect of film multi-scale structure on the water vapor permeability in hydroxypropyl starch (HPS)/Na-MMT nanocomposites.

    PubMed

    Liu, Siyuan; Cai, Panfu; Li, Xiaoxi; Chen, Ling; Li, Lin; Li, Bing

    2016-12-10

    To improve the water vapor resistance of starch-based films, Na-MMT (Na-montmorillonite) as nanofillers were fabricated into hydroxypropyl starch and the multi-scale structural changes (including intermolecular interaction, short-range conformation, long-range ordered structure and the aggregated structure of the film) were revealed. The elongation of the water vapor molecule pathway by tortuous path is generally recognized as the main reason for the improvement of water resistance. However this study observed the lowest water vapor permeability (WVP) was at the 3% Na-MMT/hydroxypropyl starch (HPS) ratio instead of 5% even nanofillers were partially exfoliated at both ratio. Except for the "tortuous path" caused by nanofillers, this observation proposed that the short-range conformation of HPS chains, long-range ordered structure and the aggregated structure likely influenced the water barrier property. The relationship between WVP and multi-scale structure of the film was investigated. The results suggested that a good balance of short-range conformationin the amorphous region, long-range ordered structure and the aggregated structure of the film was required for the improvement of water vapor barrier property. PMID:27577909

  2. An automated airplane detection system for the safeguard against airplane illumination from the laser guide star beacons at the MMT

    NASA Astrophysics Data System (ADS)

    Snyder, Miguel; Lloyd-Hart, Michael

    2007-09-01

    Laser beams for guide star generation are a potential hazard for aircraft. At the MMT telescope located on Mt. Hopkins in Southern Arizona, a constellation of five Rayleigh guide stars is created with a total of 25 W of projected power at 532 nm wavelength. We report operational results from an automatic system deployed at the MMT that is designed to detect aircraft and shut down the lasers if a collision with the beams appears likely. The system, building on a previous prototype, uses a wide-angle CCD camera mounted with a minimally unobstructed view to the optical support structure at the top of the telescope. A computer program reads the camera once every two seconds and calculates the difference between adjacent image pairs. The anti-collision beacons required on all aircraft by the Federal Aviation Administration appear as streaks in the field. If an airplane is detected, it is located in the field relative to the laser beam and its path is projected. If aircraft are detected near or appear that they will approach the beam, the laser's safety shutter is closed and warning messages are sent to the laser operator. Failsafe operation is assured by a "heart beat" signal continuously sent from the detection system to the laser controller, and by the fact that the safety shutter must be energized to open. In the event of a power failure, the system must be manually reset by the Laser Safety Officer before the laser beam can again be propagated.

  3. Full-system laboratory testing of the F/15 deformable secondary mirror for the new MMT adaptive optics system

    NASA Astrophysics Data System (ADS)

    Mcguire, Patrick C.; Lloyd-Hart, Michael; Angel, J. Roger P.; Angeli, George Z.; Johnson, Robert L.; Fitz-Patrick, Bruce C.; Davison, Warren B.; Sarlot, Roland J.; Bresloff, Cynthia J.; Hughes, John M.; Miller, Stephen M.; Schaller, Skip; Wildi, Francois P.; Kenworthy, Matthew A.; Cordova, Richard M.; Rademacher, Matthew J.; Rascon, Mario H.; Burge, James H.; Stamper, Brian L.; Zhao, Chunyu; Salinari, Piero; del Vecchio, Ciro; Riccardi, Armando; Brusa, Guido; Biasi, Roberto; Andrighettoni, Mario; Gallieni, Daniele; Franchini, Claudio; Sandler, David G.; Barrett, Todd K.

    1999-09-01

    We will present a system to perform closed-loop optical tests of the 64 cm diameter, 336 actuator adaptive secondary made at the Steward Observatory Mirror Laboratory. Testing will include Shack-Hartmann wavefront sensing and modal correction of static and dynamic aberrated wavefronts. The test optical system is designed so that experiments can be made with both the focal plane instrument and secondary installed in their normal configuration at the MMT, or with the same 9 m spacing in a laboratory test tower. The convex secondary will be illuminated at normal incidence through two 70 cm diameter lenses mounted just below. The artificial, aberrated star is projected from near the wavefront sensor in the Cassegrain focus assembly. Computer generated holograms correct for spherical aberration in the really optics at the test wavelengths of 0.594 and 1.5 micrometers . Atmospheric turbulence is reproduced by two spinning transmission plates imprinted with Kolmogorov turbulence. The Shimmulator will give us the opportunity to test fully the adaptive optics system before installation at the new MMT, hence saving much precious telescope time.

  4. A SEARCH FOR OCCULTATIONS OF BRIGHT STARS BY SMALL KUIPER BELT OBJECTS USING MEGACAM ON THE MMT

    SciTech Connect

    Bianco, F. B.; Lehner, M. J.; Protopapas, P.; McLeod, B. A.; Alcock, C. R.; Holman, M. J.

    2009-08-15

    We conducted a search for occultations of bright stars by Kuiper Belt Objects (KBOs) to estimate the density of subkilometer KBOs in the sky. We report here the first results of this occultation survey of the outer solar system conducted in 2007 June and 2008 June/July at the MMT Observatory using Megacam, the large MMT optical imager. We used Megacam in a novel shutterless continuous-readout mode to achieve high-precision photometry at 200 Hz, which with point-spread function convolution results in an effective sampling of {approx}30 Hz. We present an analysis of 220 star hours of data at a signal-to-noise ratio of 25 or greater, taken from images of fields within 3 deg. of the ecliptic plane. The survey efficiency is greater than 10% for occultations by KBOs of diameter d {>=} 0.7 km, and we report no detections in our data set. We set a new 95% confidence level upper limit for the surface density {sigma} {sub N}(d) of KBOs larger than 1 km: {sigma} {sub N}(d {>=} 1 km) {<=} 2.0 x 10{sup 8} deg{sup -2}, and for KBOs larger than 0.7 km {sigma} {sub N}(d {>=} 0.7 km) {<=} 4.8 x 10{sup 8} deg{sup -2}.

  5. Geothermal exploration using audio-magnetotelluric in Pariangan Tanah Datar, West Sumatra

    NASA Astrophysics Data System (ADS)

    Saputra, Andriyan; Widodo, Kholid, Muhammad

    2015-04-01

    The existence of Mt. Marapi in Pariangan Tanah Datar has a big potential of geothermal energy resource. The study area is located in southeastern Mt. Marapi. The geological elements correspond to lava granitic, sandstone quartz, quartzite and conglomerate. The aim of this research is to investigate the geothermal system in this area. Measurements of audio-magnetotelluric (AMT) long line are 10 km with two profiles. The audio-magnetotelluric (AMT) data carried out during July 2014. The models result were done by using 1-D inversion technique. The 1-D inversion was done with Occam and Marquadt algoritm. We assumed that for the first layer indicates as the conductive zone (±10 Ωm), the second layer as the reservoir geothermal system (±100 Ωm) that contains with sandstone quartz, and the third layer can be interpreted as volcanic rock (±1000 - 10000 Ωm) which is the basement of geothermal system.

  6. Magnetotelluric study of the Xuefeng mountain area, Hu'nan Province, China

    NASA Astrophysics Data System (ADS)

    Chen, Musen; Xue, Lingxiang; Wang, Yousheng; Zhu, Shengjun

    2016-03-01

    A magnetotelluric study was carried out in the Xuefeng mountain uplift belt and its western margins. A detailed investigation was made of the resistivity of the formations, and reliable data were obtained. The sedimentary cover and basement structure of the Xuefeng mountain area and the deep geological structure were analyzed in detail using magnetotelluric data from the two-dimensional inversion of the resistivity profile data in combination with regional gravity and magnetic data. It was concluded that the tectonic movements were characterized by basement detachment, and north-south ramp. The study area can be divided into a southern uplift zone, a southern thrust-faulted zone, a central uplift zone, and a northern depression zone. This work has provided geophysical evidence that can be used in future studies of the tectonics and petroleum geology of this region.

  7. Magnetotelluric study of the Xuefeng mountain area, Hu'nan Province, China

    NASA Astrophysics Data System (ADS)

    Chen, Musen; Xue, Lingxiang; Wang, Yousheng; Zhu, Shengjun

    2016-04-01

    A magnetotelluric study was carried out in the Xuefeng mountain uplift belt and its western margins. A detailed investigation was made of the resistivity of the formations, and reliable data were obtained. The sedimentary cover and basement structure of the Xuefeng mountain area and the deep geological structure were analyzed in detail using magnetotelluric data from the two-dimensional inversion of the resistivity profile data in combination with regional gravity and magnetic data. It was concluded that the tectonic movements were characterized by basement detachment, and north-south ramp. The study area can be divided into a southern uplift zone, a southern thrust-faulted zone, a central uplift zone, and a northern depression zone. This work has provided geophysical evidence that can be used in future studies of the tectonics and petroleum geology of this region.

  8. Adsorption of PolyCarboxylate Poly(ethylene glycol) (PCP) esters on Montmorillonite (Mmt): effect of exchangeable cations (Na+, Mg2+ and Ca2+) and PCP molecular structure.

    PubMed

    Ait-Akbour, Rachid; Boustingorry, Pascal; Leroux, Fabrice; Leising, Frédéric; Taviot-Guého, Christine

    2015-01-01

    This study deals with the adsorption of PolyCarboxylate Poly(ethylene glycol) esters (PCP) superplasticizers on Na-, Mg- and Ca-saturated Montmorillonite (Mmt) clays. The interactions have been examined through different experimental methods: adsorption isotherms, zeta potential measurements and sedimentation experiments. It was found that PCP adsorption depends both on the architecture of PCP molecules and the nature of cation located on the interlayer exchange sites of the Montmorillonite. Whatever the PCP, a larger amount was adsorbed on Na-Mont than on Mg-Mont or Ca-Mont. This indicates the occurrence of two adsorption mechanisms: (i) a superficial adsorption via electrostatic interactions between the carboxylate groups of PCP and positively charged sites on clay surfaces, (ii) intercalation of ether units of the PCP grafts in the interlayer space by displacement of water molecules coordinated to the exchangeable cations. Furthermore, despite the weak negative values of the zeta potential, the addition of PCP promotes the stability of the suspensions which is attributed to steric repulsion acting between particles. PMID:25313488

  9. Assembly of luminescent ordered multilayer thin-films based on oppositely-charged MMT and magnetic NiFe-LDHs nanosheets with ultra-long lifetimes.

    PubMed

    Liu, Meitang; Wang, Tianlei; Ma, Hongwen; Fu, Yu; Hu, Kunran; Guan, Chao

    2014-01-01

    In this present report, luminescent ordered multilayer thin films (OMFs) based on oppositely-charged inorganic nanosheets and the different oppositely-charged chromophores were fabricated via layer-by-layer assembly method. Exfoliated layered double hydroxides (LDHs) and montmorillonite (MMT) nanosheets with opposite charges can be expected to provide a pseudo electronic microenvironment (PEM) which has not been declared in previous literatures, and transition metal-bearing LDHs nanosheets can offer an additional ferromagnetic effect (FME) for the chromophores at the same time. Surprisingly, the luminescent lifetimes of those OMFs with PEM and FME are significantly prolonged compared with that of the pristine chromophores, even much longer than those of OMFs without oppositely-charged and ferromagnetic architecture. Therefore, it is highly expected that the PEM and FME formed by oppositely-charged and transition metal-bearing inorganic nanosheets have remarkable influence on obtaining better optical property, which suggests a new potential way to manipulate, control and develop the novel light-emitting materials and optical devices. PMID:25413710

  10. Assembly of luminescent ordered multilayer thin-films based on oppositely-charged MMT and magnetic NiFe-LDHs nanosheets with ultra-long lifetimes

    PubMed Central

    Liu, Meitang; Wang, Tianlei; Ma, Hongwen; Fu, Yu; Hu, Kunran; Guan, Chao

    2014-01-01

    In this present report, luminescent ordered multilayer thin films (OMFs) based on oppositely-charged inorganic nanosheets and the different oppositely-charged chromophores were fabricated via layer-by-layer assembly method. Exfoliated layered double hydroxides (LDHs) and montmorillonite (MMT) nanosheets with opposite charges can be expected to provide a pseudo electronic microenvironment (PEM) which has not been declared in previous literatures, and transition metal-bearing LDHs nanosheets can offer an additional ferromagnetic effect (FME) for the chromophores at the same time. Surprisingly, the luminescent lifetimes of those OMFs with PEM and FME are significantly prolonged compared with that of the pristine chromophores, even much longer than those of OMFs without oppositely-charged and ferromagnetic architecture. Therefore, it is highly expected that the PEM and FME formed by oppositely-charged and transition metal-bearing inorganic nanosheets have remarkable influence on obtaining better optical property, which suggests a new potential way to manipulate, control and develop the novel light-emitting materials and optical devices. PMID:25413710

  11. Synthesis of the very acid-sensitive Fmoc-Cys(Mmt)-OH and its application in solid-phase peptide synthesis.

    PubMed

    Barlos, K; Gatos, D; Hatzi, O; Koch, N; Koutsogianni, S

    1996-03-01

    S-4-methoxytrityl cysteine was synthesized and converted into the corresponding Fmoc-Cys(Mmt)-OH by its reaction with Fmoc-OSu. As compared to the corresponding Fmoc-Cys(Trt)-OH, the S-Mmt-function was found to be considerably more acid labile. Quantitative S-Mmt-removal occurs selectively in the presence of groups of the tert butyl type and S-Trt by treatment with 0.5-1.0% TFA. The new derivative was successfully utilized in the SPPS of Tyr1-somatostatin on 2-chlorotrityl resin. In this synthesis groups of the Trt-type were exclusively used for amino acid side-chain protection. Quantitative cleavage from the resin and complete deprotection was performed by treatment with 3% TFA in DCM-TES (95:5) for 30 min at RT. We observed no reduction of tryptophan under these conditions. PMID:8740963

  12. Numerical Simulation of Response Characteristics of Audio-magnetotelluric for Gas Hydrate in the Qilian Mountain Permafrost, China

    NASA Astrophysics Data System (ADS)

    Xiao, Kun; Zou, Changchun; Yu, Changqing; Pi, Jinyun

    2015-10-01

    Audio-magnetotelluric (AMT) method is a kind of frequencydomain sounding technique, which can be applied to gas hydrate prospecting and assessments in the permafrost region due to its high frequency band. Based on the geological conditions of gas hydrate reservoir in the Qilian Mountain permafrost, by establishing high-resistance abnormal model for gas hydrate and carrying out numerical simulation using finite element method (FEM) and nonlinear conjugate gradient (NLCG) method, this paper analyzed the application range of AMT method and the best acquisition parameters setting scheme. When porosity of gas hydrate reservoir is less than 5%, gas hydrate saturation is greater than 70%, occurrence scale is less than 50 m, or bury depth is greater than 500 m, AMT technique cannot identify and delineate the favorable gas hydrate reservoir. Survey line should be more than twice the length of probable occurrence scale, while tripling the length will make the best result. The number of stations should be no less than 6, and 11 stations are optimal. At the high frequency section (10~1000 Hz), there should be no less than 3 frequency points, 4 being the best number.

  13. Two-dimensional magnetotelluric characterization of the El Hito Anticline (Loranca Basin, Spain)

    NASA Astrophysics Data System (ADS)

    Piña-Varas, Perla; Ledo, Juanjo; Queralt, Pilar; Roca, Eduard; García-Lobón, Jose L.; Ibarra, Pedro; Biete, Cristina

    2013-08-01

    Magnetotelluric surveys were conducted to investigate the structure in the El Hito Anticline in the southern Loranca Basin, Spain. The structure of this anticline is partly known from nearby data (geological cross sections, geological maps, well-logs) from vintage geophysical and geological basin-scale surveys. Unfortunately, these surveys do not have the appropriate resolution to determine certain characteristics of the anticline accurately, such as the thickness or geometry of geological units. To address this deficiency, magnetotelluric data were acquired at 51 sites along three profiles to image the electrical resistivity of the anticline. To identify a geologically reasonable resistivity model, a conceptual model based on previous geological and geophysical information (cross sections and well-log data) was generated. Several inversions were performed using the conceptual model, which played a key role in the interpretation of the magnetotelluric data, and the construction of a suitable initial model was essential in producing geologically meaningful models. Using these results, we obtained 2-D resistivity models that provide information on the main geological units and structures. We also performed sensitivity tests to understand the morphology and structure of the resistive basement better. The results indicate the presence of basement highs that show different structural styles for the basement and its cover, and an increase in the basement depth towards the south. The final 2-D resistivity models provide new information regarding the structure of the anticline and demonstrate a clear correlation between the main geological units and resistivity, as well as correlations with mapped surface faults.

  14. Hydrothermal System of the Lastarria Volcano (Central Andes) Imaged by Magnetotellurics

    NASA Astrophysics Data System (ADS)

    Diaz, D.

    2015-12-01

    Lazufre volcanic complex, located in the central Andes, is recently undergoing an episode of uplift, conforming one of the most extensive deforming volcanic systems worldwide. Recent works have focused on the subsurface of this volcanic system at different scales, using surface deformation data, seismic noise tomography and magnetotellurics. Here we image the electrical resistivity structure of the Lastarria volcano, one of the most important features in the Lazufre area, using broadband magnetotelluric data at 30 locations around the volcanic edifice. Results from 3-D modeling show a conductive zone at 6 km depth south of the Lastarria volcano interpreted as a magmatic heat source, which is connected to a shallower conductive area beneath the volcanic edifice and its close vicinity. This shallow highly conductive zone fits with geochemical analysis results of thermal fluid discharges, related to fumaroles present in this area, in terms of depth extent and possible temperatures of fluids, and presents also a good correlation with seismic tomography results. The horizontal extension of this shallow conductive zone, related to the hydrothermal system of Lastarria, suggests that it has been draining one of the lagoons in the area (Laguna Azufrera), forming a sulfur rich area which can be observed at the southern side of this lagoon. Joint modeling of the hydrothermal system using magnetotellurics and seismic data is part of the current work.

  15. 3-D inversion of magnetotelluric data using unstructured tetrahedral elements: applicability to data affected by topography

    NASA Astrophysics Data System (ADS)

    Usui, Yoshiya

    2015-08-01

    A 3-D magnetotelluric (MT) inversion code using unstructured tetrahedral elements has been developed in order to correct the topographic effect by directly incorporating it into computational grids. The electromagnetic field and response functions get distorted at the observation sites of MT surveys because of the undulating surface topography, and without correcting this distortion, the subsurface structure can be misinterpreted. Of the two methods proposed to correct the topographic effect, the method incorporating topography explicitly in the inversion is applicable to a wider range of surveys. For forward problems, it has been shown that the finite element method using unstructured tetrahedral elements is useful for the incorporation of topography. Therefore, this paper shows the applicability of unstructured tetrahedral elements in MT inversion using the newly developed code. The inversion code is capable of using the impedance tensor, the vertical magnetic transfer function (VMTF), and the phase tensor as observational data, and it estimates the subsurface resistivity values and the distortion tensor of each observation site. The forward part of the code was verified using two test models, one incorporating topographic effect and one without, and the verifications showed that the results were almost the same as those of previous works. The developed inversion code was then applied to synthetic data from a MT survey, and was verified as being able to recover the resistivity structure as well as other inversion codes. Finally, to confirm its applicability to the data affected by topography, inversion was performed using the synthetic data of the model that included two overlapping mountains. In each of the cases using the impedance tensor, the VMTF and the phase tensor, by including the topography in the mesh, the subsurface resistivity was determined more proficiently than in the case using the flat-surface mesh. Although the locations of the anomalies were

  16. Case histories of electrical resistivity and controlled-source magnetotelluric surveys for the site investigation of tunnel construction

    SciTech Connect

    Kwon, H.S.; Song, Y.; Yi, M.J.; Chung, H.J.; Kim, K.S.

    2006-12-15

    In tunnel construction, the information regarding rock mass quality and the distribution of weak zones is crucial for economical tunnel design and to ensure safety. Usually, the rock mass grade is estimated by observing recovered cores obtained by drilling or by physical parameters calculated in a laboratory using core samples. However, the high drilling cost limits the number of boreholes; furthermore, rough terrains can reduce the access of drilling machines to the survey sites. In such situations, surface geophysical methods such as electrical resistivity or controlled-source magnetotelluric (CSMT) can provide a rough estimate of the rock mass condition over the planned tunnel route. These methods can also map weak zones (faults, fractures, coal bearing zones, and cavities), which are characterized by a lower resistivity than the surrounding fresh rock mass. We present two successful applications of the electrical resistivity and CSMT methods to the site investigation of tunnel construction over a rough terrain. The first example demonstrates that the boundary of the bedrock and weak zones related to the distribution of coaly shale and coal seams were estimated to extend beyond a few hundred meters below the rough surface. The second example shows that the developing direction and depth of cavities, which are mainly related to the weak zones in limestone, were successfully interpreted by a three-dimensional (3-D) electrical resistivity survey with the aid of borehole test results.

  17. The lithospheric architecture of a Neoproterozoic collision zone in Southern Africa inferred from deep probing magnetotelluric data

    NASA Astrophysics Data System (ADS)

    Khoza, D. T.; Jones, A. G.; Muller, M. R.; Evans, R. L.; Miensopust, M. P.; Hamilton, M.; Garcia, X. A.; Cole, P.; Ngwisanyi, T.; Hutchins, D.; Fourie, S.; Jelsma, H.; Pettit, W.; Aravanis, T.; Webb, S. J.; Wasborg, J.

    2009-12-01

    Cratonic margins have played a major role in shaping the modern Southern African tectonic landscape, and central to our knowledge is information about the lithospheric-scale structures and geometries using geophysical methods. Understanding the evolution of the younger orogenic belts around Archean cratons using electrical resistivity data is one of the primary objectives of the Southern African Magnetotelluric Experiment (SAMTEX); the largest ever land-based magnetotelluric (MT) project. MT data were acquired along four profiles crossing the enigmatic Rehoboth Terrane, the Neo-Proterozoic Ghanzi-Chobe/Damara belts (collectively termed the Damara Mobile Belt, DMB) and the southern Angola craton. The extended Groom and Bailey distortion decomposition technique was applied to the MT data and analyses show significant depth and along-profile variations in geo-electric strike and dimensionality on all transects crossing these three tectonic units (i.e. Rehoboth Terrane, Angola craton and the DMB). Geo-electric strikes are generally parallel to the north-east trending tectonic fabric, as inferred from the magnetic data, but the significant strike variations with depth are expressions of heterogeneity in lithospheric structure. Electrical resistivity models derived from the data provide the first pseudo three-dimensional tectonic structure of the Damara orogen and adjacent terranes. Regional-scale resistivity models constructed from two-dimensional inversions of the MT data indicate significant variations in lithospheric resistivity structure along and across strike from the younger orogen to the older adjacent cratons. The Damara belt lithosphere, although generally more conductive and significantly thinner than adjacent Angola craton and Rehoboth terrane, exhibits upper resistive upper crustal features tentatively interpreted to be caused by igneous intrusions emplaced during Pan-African magmatic event. Upper crustal listric faults are imaged as conductive features and

  18. An approach for monitoring resistivity variations using surface magnetotelluric data and its application to CO2 storage site

    NASA Astrophysics Data System (ADS)

    Ogaya, X.; Ledo, J.; Queralt, P.; Jones, A. G.; Marcuello, A.

    2014-12-01

    In this work we present an approach to perform electromagnetic (EM) monitoring using surface magnetotelluric (MT) data. The proposed methodology, called layer stripping, is based on the analytical solution of the one-dimensional MT problem and the fact that resolution to resistivity changes produced at a given depth increase when increasing the depth at which data are acquired. Thus, giving a well-known geoelectrical baseline model of a reservoir site, the layer stripping approach aims to remove the effect of the upper, unchanging, structures in order to obtain the time-varying MT responses at the target depth. In this paper the proposed method is tested and validated using the 3D geoelectrical baseline model of the Hontomín site (Spain) for CO2 geological storage in a deep saline aquifer. The 3D resistivity model of Hontomín defines the subsurface in the pre-injection state, showing the dome-like structure of the saline aquifer and imaging the principal set of faults. For monitoring purposes, the model allows obtaining the MT responses at the main reservoir depth using the layer stripping approach to remove the upper structures not affected by the injection of the gas. The results obtained in this work suggest that the layer stripping method improves the resolution of surface MT responses being able to detect smaller resistivity changes.

  19. Crustal and lithospheric imaging of the Atlas Mountains of Morocco inferred from magnetotelluric data

    NASA Astrophysics Data System (ADS)

    Kiyan, D.; Jones, A. G.; Fullea, J.; Hogg, C.; Ledo, J.; Sinischalchi, A.; Campanya, J.; Picasso Phase II Team

    2010-12-01

    The Atlas System of Morocco is an intra-continental mountain belt extending for more than 2,000 km along the NW African plate with a predominant NE-SW trend. The System comprises three main branches: the High Atlas, the Middle Atlas, and the Anti Atlas. We present the results of a very recent multi-institutional magnetotelluric (MT) experiment across the Atlas Mountains region that started in September, 2009 and ended in February, 2010, comprising acquisition of broadband and long-period MT data. The experiment consisted of two profiles: (1) a N-S oriented profile crossing the Middle Atlas through the Central High Atlas to the east and (2) a NE-SW profile crossing the western High Atlas towards the Anti Atlas to the west. The MT measurements are part of the PICASSO (Program to Investigate Convective Alboran Sea System Overturn) and the concomitant TopoMed (Plate re-organization in the western Mediterranean: Lithospheric causes and topographic consequences - an ESF EUROCORES TOPO-EUROPE project) projects, to develop a better understanding of the internal structure and evolution of the crust and lithosphere of the Atlas Mountains. The MT data have been processed with robust remote reference methods and submitted to comprehensive strike and dimensionality analysis. Two clearly depth-differentiated strike directions are apparent for crustal (5-35 km) and lithospheric (50-150 km) depth ranges. These two orientations are roughly consistent with the NW-SE Africa-Eurasia convergence acting since the late Cretaceous, and the NNE-SSW Middle Atlas, where Miocene to recent Alkaline volcanism is present. Two-dimensional (2-D) smooth electrical resistivity models were computed independently for both 50 degrees and 20 degrees E of N strike directions. At the crustal scale, our preliminary results reveal a middle to lower-crustal conductive layer stretching from the Middle Atlas southward towards the High Moulouya basin. The most resistive (and therefore potentially thickest

  20. Amphibious Magnetotelluric Investigation of the Aleutian Arc: Mantle Melt Generation and Migration beneath Okmok Caldera

    NASA Astrophysics Data System (ADS)

    Zelenak, G.; Key, K.; Bennington, N. L.; Bedrosian, P.

    2015-12-01

    Understanding the factors controlling the release of volatiles from the downgoing slab, the subsequent generation of melt in the overlying mantle wedge, the migration of melt to the crust, and its evolution and emplacement within the crust are important for advancing our understanding of arc magmatism and crustal genesis. Because melt and aqueous fluids are a few orders of magnitude more electrically conductive than unmelted peridotite, the conductivity-mapping magnetotelluric (MT) method is well-suited to imaging fluids and melt beneath arc volcanoes. Here we present conductivity results from an amphibious MT profile crossing Okmok volcano in the central Aleutian arc. The Aleutian arc is one of the most volcanically active regions in North America, making it an ideal location for studying arc magnetism. Okmok volcano, located on the northeastern portion of Umnak Island, is among the most active volcanoes in the Aleutian chain. In addition to two caldera-forming events in the Holocene, numerous eruptions in the past century indicate a robust magmatic supply. Previous coarse resolution seismic studies have inferred a crustal magma reservoir. In order to investigate the role fluids play in melting the mantle wedge, how melts ascend through the corner flow regime of the mantle wedge, how melt migrates and is stored within the upper mantle and crust, and how this impacts explosive caldera forming eruptions, we carried out an amphibious geophysical survey across the arc in June-July 2015. Twenty-nine onshore MT stations and 10 offshore stations were collected in a 3D array covering Okmok, and 43 additional offshore MT stations completed a 300 km amphibious profile starting at the trench, crossing the forearc, arc and backarc. Thirteen onshore passive seismic stations were also installed and will remain in place for one year to supplement the twelve permanent stations on the island. Data collected by this project will be used to map seismic velocity and electrical

  1. The upper crust of the Scandinavian Caledonides as seen by Magnetotellurics

    NASA Astrophysics Data System (ADS)

    Yan, Ping; Garcia Juanatey, Maria A.; Kalscheuer, Thomas; Juhlin, Christopher

    2015-04-01

    As part of the Collisional Orogeny in the Scandinavian Caledonides (COSC) project, broadband magnetotelluric (MT) data were acquired along a 60 km long profile following recent seismic reflection surveys. In total, 78 MT sites were installed with an inter-site spacing varying between 600 and 1000 m. The aims of this study are to provide resistivity information on the upper crust of the mountain belt and, together with other geophysical investigations, to better delineate the structures of the orogen and the processes that shaped it. Additionally, the MT data are expected to help determine the location of a future borehole, COSC-2. COSC-2 is planned to drill through the décollement zone associated to the graphitic rich alum shales. Since these shales are highly conductive, they are an excellent target for the MT method. Besides the long MT profile, one short profile with 5 stations was acquired nearby the already existing COSC-1 drill site to increase areal coverage and better constrain 3D resistivity structures. The new 3D information improves the existing 3D geological model around the borehole, that has been interpreted from seismic reflection and potential field data. The impedance functions were calculated using a robust statistical procedure and the remote reference technique. MT data from Norway recorded at the same time in a field campaign by Oulu University were used for remote referencing. The data quality of the obtained transfer functions varies along the profile, being very good in remote areas, but quite noisy close to cities. Thus, a careful selection of the data set was necessary prior to analysis and modelling. 2D resistivity models of the 60 km long profile were estimated through inversion using the determinant of the impedance tensor, the TE mode, the TM mode, and the combination of TE and TM modes. The main features shared by the models are a resistor lying beneath COSC-1 extending down to about 2 km depth, a shallow resistor further to the east

  2. 2-D magnetotelluric experiment to investigate the Nassugtoqidian orogeny in South-East Greenland

    NASA Astrophysics Data System (ADS)

    Heincke, Björn; Chen, Jin; Riisager, Peter; Kolb, Jochen; Jørgensen, Asta F.

    2015-04-01

    The northwest-trending Palaeoproterozoic Nagssugtoqidian orogen extends over 250 km along the east coast of Greenland in the area around the village Tasiilaq. The geological evolution of this area closely compares with the ones of the Lewisian complex of Scotland and the Nagssugtoqidian orogen in western Greenland and, hence, leads to the suggestion that they belong to the same continental-scale orogenic belt. However, an accurate correlation across the inland ice is challenging and still ambiguous and therefore more detailed knowledge about the individual orogens might help to understand their relationship. Details about the large-scale tectonic evolution during the Nagssugtoqidian orogeny in this remote Arctic region are not known due to complex geology, relatively coarse geological mapping and the lack of extensive geophysical investigations. E.g. the vergence of the orogen, subduction-related magmatism and accretion history are matters of ongoing discussion (Kalsbeek et al., 1993; Nutman et al., 2008 and Kolb, 2013). We performed a 2-D magnetotelluric (MT) experiment across the southern part of the orogen along the Sermilik Fjord in order to improve our understanding of the orogenic process in general and to better constrain the location and vergence of the suture zone. However, because of the rough climate and the lack of infrastructure, this study is considered as a first test to investigate how MT surveys can be most efficiently performed in this remote part of the world. The NE-SW trending profile consists of eight MT stations and has a total length of ~70 km using long period LEMI-420 systems. The quality of the data is severely affected by polar electrojets that do not satisfy the plane wave assumptions, which is typical for regions close to the magnetic poles. In order to reduce the distortion from these signals onto the impedance estimates, we tested different advanced processing schemes. In addition to the more conventional robust response function

  3. Hydrogen Content Of The Mantle From Combined Magnetotelluric, Mineral Physics And Xenolith Data

    NASA Astrophysics Data System (ADS)

    Selway, K.; Karato, S.

    2012-12-01

    Determining the composition of the mantle is a significant challenge. The only direct measurements can be made from mantle xenoliths, which sample only a small fraction of the lithsopheric mantle and are unlikely to have strictly representative compositions. Therefore it is vital that geophysical data that image the mantle are also analysed and that their relationship to compositional factors is well understood. The geophysical techniques with the best resolution at mantle depths are seismic tomography and magnetotellurics (MT). MT is a passive electromagnetic method that relies on the fact that the Earth's time-varying magnetic field induces electrical currents in conductive bodies within the Earth and thus images the electrical resistivity structure of the Earth. Mineral physics experiments on the nominally anhydrous silicates that dominate the continental mantle have shown that, at a given temperature, their electrical conductivities are very sensitive to small amounts of hydrogen while being relatively insensitive to major element composition. The combination of MT data and experimental mineral physics data is therefore a powerful tool to constrain the hydration state of the mantle. However, in order to obtain reliable estimates of water content, the influence of other factors such as temperature and oxygen fugacity needs to be analysed with a great care. With this in mind, an MT survey was carried out in north-east Tanzania, crossing from the Tanzanian Craton over the East Africa Rift. The Tanzanian Craton has remained largely stable since the Archean whereas the adjacent lithosphere has been reworked during several major orogenic events including the Paleoproterozoic Usagaran Orogen, the Neoproterozoic East African Orogen and the current East Africa Rifting. The very different responses of the Tanzanian Craton and the adjacent lithosphere to these tectonothermal events suggests that there are significant compositional differences between them. Much of the

  4. Analytic magnetotelluric responses to a two-segment model with axially anisotropic conductivity structures overlying a perfect conductor

    NASA Astrophysics Data System (ADS)

    Qin, Linjiang; Yang, Changfu

    2016-06-01

    The rocks in the crust and the upper mantle of the Earth are believed to exhibit electrical anisotropy to some extent. It is beneficial to further understand and recognize the propagation of the electromagnetic waves in the Earth by investigating the magnetotelluric (which is one of the main geophysical techniques to probe the deep structures in the Earth) responses of the media with anisotropic conductivity structures. In this study, we examine the magnetotelluric fields over an idealized 2-D model consisting of two segments with axially anisotropic conductivity structures overlying a perfect conductor basement by a quasi-static analytic approach. The resulting analytic solution could not only contribute to the electromagnetic induction theory in the anisotropic Earth but also serve as at least an initial standard solution which could be used to validate the reliability and accuracy of the numerical algorithms developed for modelling the magnetotelluric responses of the 2-D media with much more general anisotropic conductivity.

  5. Analytic magnetotelluric responses to a two-segment model with axially anisotropic conductivity structures overlying a perfect conductor

    NASA Astrophysics Data System (ADS)

    Linjiang, QIN; Changfu, YANG

    2016-03-01

    The rocks in the crust and the upper mantle of the Earth are believed to exhibit electrical anisotropy to some extent. It is beneficial to further understand and recognize the propagation of the electromagnetic waves in the Earth by investigating the magnetotelluric (which is one of the main geophysical techniques to probe the deep structures in the Earth) responses of the media with anisotropic conductivity structures. In the present study, we examine the magnetotelluric fields over an idealized 2-D model consisting of two segments with axially anisotropic conductivity structures overlying a perfect conductor basement by a quasi-static analytic approach. The resulting analytic solution could not only contribute to the electromagnetic induction theory in the anisotropic Earth but also serve as at least an initial standard solution which could be used to validate the reliability and accuracy of the numerical algorithms developed for modeling the magnetotelluric responses of the 2-D media with much more general anisotropic conductivity.

  6. Magnetotellurics with long distance remote reference to reject DC railway noise

    NASA Astrophysics Data System (ADS)

    Hanstein, T.; Jiang, J.; Strack, K.; Ritter, O.

    2014-12-01

    Some parts of railway network in Europe is electrified by DC current. The return current in the ground is varying in space, time and power when the train is moving. Since the train traffic is active 24 hours, there is no quite time. The train signal is dominating for periods longer than 1 s and is a near field source. The transfer function of the magnetotelluric sounding (MT) is influenced by this near field source, the phase is going to zero and amplitude increase with slope 1 for longer periods. Since this dominating noise is present all day robust magnetotelluric processing technique to identify and remove outliers are not applicable and sufficient. The remote reference technique has successfully been applied for magnetotelluric soundings Combining an disturbed local MT data set with the data of the remote station, which is recording simultaneously the horizontal magnetic fields, can improve the data quality. Finding a good remote station during field survey is difficult and expensive. There is a permanent MT remote reference station in Germany. The set up and maintance is done by the GFZ - Helmholtz Centre Potsdam - GFZ German Research Centre for Geosciences. The location is near Wittstock and has good signal-to-noise-ratio with low cutural noise, the ground is almost lD and recording since May 2010. The electric and magnetic field is continously recorded with 250 Hz sampling and induction coils. The magnetic field is also recorded with fluxgate magnetometers and 5 Hz sampling. The distance to the local MT site is about 600 km.

  7. New facilities for magnetotelluric sounding and electromagnetic sounding with active sources

    NASA Astrophysics Data System (ADS)

    Klymovych, Y.; Rakhlin, L.; Tregubenko, V.

    2003-04-01

    Magnetotelluric (MT) sounding and investigations that use electromagnetic sounding with active sources (SAS) are wide spread in many branch of geophysics. The main goal of their application is Earth geoelectric cross-section parameters definition. For MT sounding it was possible to carry out it mostly till the time intervals less, than 10000 sec, that does not permitted to get the sections for the depth more than some first kilometres. Last years in LCISR the new generation of MT and facilities for deep electromagnetic sounding in ultra-low frequencies periods up to 200,000 sec were designed. It became possible after the development of highly stable devices for DC magnetic and telluric measurements. The long term stability of newly created magnetometers now is better than 0.5 nT per month and temperature stability about 0.1 nT/oC. For telluric currents measurements highly stable non-polarized electrodes with long term stability better than 60 mV per month, and temperature stability about 10 mV/oC were designed. Implementation of such facilities made it possible to realize the magnetotelluric sounding to the depth 400-600 km and the experimental results have good agreement with global magnetotelluric curve. Such MT stations (LEMI-404 model) were used in BEAR (Baltic Electromagnetic Array Research) and several others projects. Their use made it possible also to prove with very high probability the existence of low-depth astenosphere in Dnepre-Donetsk Basin (Ukraine). Now a batch of these MT stations is manufactured and used in Ukrainian magnetotelluric net. This net was intended firstly for investigation of electromagnetic earthquake precursors, but after its further development - for geoelectric section circular changes too. Recently two new MT stations are developed. First one low-frequency (DC 1 Hz) inexpensive station LEMI-411 which, having as high metrological parameters as the wide-band one, costs considerebly lower. Second one is multifunctional SAS station

  8. MT3D: a 3 dimensional magnetotelluric modeling program (user's guide and documentation for Rev. 1)

    SciTech Connect

    Nutter, C.; Wannamaker, P.E.

    1980-11-01

    MT3D.REV1 is a non-interactive computer program written in FORTRAN to do 3-dimensional magnetotelluric modeling. A 3-D volume integral equation has been adapted to simulate the MT response of a 3D body in the earth. An integro-difference scheme has been incorporated to increase the accuracy. This is a user's guide for MT3D.REV1 on the University of Utah Research Institute's (UURI) PRIME 400 computer operating under PRIMOS IV, Rev. 17.

  9. Two-dimensional magnetotelluric and gravity models of the Tuzgle volcano zone (Jujuy province, Argentina)

    NASA Astrophysics Data System (ADS)

    Sainato, Claudia M.; Pomposiello, Maria C.

    1997-07-01

    The Tuzgle volcano (24 ° 03'S, 66 ° 29'W) is situated in the southern part of the South American Andean Altiplano (Puna). The region has several geothermal manifestations. A 2-D magnetotelluric model of resistivity distribution and a 3-D gravity anomaly of the area have been proposed. A highly conductive and low density body is probably associated with a magma chamber surrounded by free saline fluids with its top at about 8 km depth. The release of fluids might be caused by the chemical reactions generated at the subduction plate of Nazca in contact with the South American plate.

  10. Topographic effect on Radio-Magnetotelluric and Slingram signals: application to a levee along the Loire river, France.

    NASA Astrophysics Data System (ADS)

    Duval, Rodolphe; Fauchard, Cyrille; Antoine, Raphael

    2014-05-01

    We study the influence of the topography of a levee on the electric and magnetic signals obtained with the Radio-Magnetotelluric method (RMT) and the Slingram method, respectively. For the RMT method, field measurements have been modelled with a finite element commercial software (AC/DC and Radio-Frequency modules of Comsol Multiphysics). A levee situated in Orléans (France) along the Loire river has been considered in order to design a model taking into account the skin depth and the incident wavelength. The effect of the incident electromagnetic field direction has been assessed with two different incident wave directions: BBC 5 from Salford (UK) and France-Inter from Allouis (France). The simulations highlight the tri-dimensional effects of the topography in the apparent resistivity, observed on the crest of the levee, depending on the incident field direction and topography. For the Slingram method, the magnetic field has been simulated using the AC/DC module of Comsol. The ratio of the primary magnetic field on the secondary one, received in a loop is determined above a straight levee. The study aims to show the various responses obtained in function of both vertical and horizontal coil configurations. We show that the signal also depends on the topography and the right configuration of the coils alignment with respect to the levee stretch direction. In this study, a buried gas pipe is also characterized by the two methods. Numerical modelling of 3D electromagnetic effects on geophysical signals helps to interpret the field measurements and offers to the stakeholder an optimized methodology for geophysical surveys on levees.

  11. Magnetotelluric survey to locate the Archean-Proterozoic suture zone in the northeastern Great Basin, Nevada, Utah, and Idaho

    USGS Publications Warehouse

    Sampson, Jay A.; Rodriguez, Brian D.

    2013-01-01

    North-central Nevada contains a large amount of gold in linear belts, the origin of which is not fully understood. During July 2008, September 2009, and August 2010, the U.S. Geological Survey, as part of the Assessment Techniques for Concealed Mineral Resources project, collected twenty-three magnetotelluric soundings along two profiles in Box Elder County, Utah; Elko County, Nevada; and Cassia, Minidoka, and Blaine Counties, Idaho. The main twenty-sounding north-south magnetotelluric profile begins south of Wendover, Nev., but north of the Deep Creek Range. It continues north of Wendover and crosses into Utah, with the north profile terminus in the Snake River Plain, Idaho. A short, three-sounding east-west segment crosses the main north-south profile near the northern terminus of the profile. The magnetotelluric data collected in this study will be used to better constrain the location and strike of the concealed suture zone between the Archean crust and the Paleoproterozoic Mojave province. This report releases the magnetotelluric sounding data that was collected. No interpretation of the data is included.

  12. New application of wavelets in magnetotelluric data processing: reducing impedance bias

    NASA Astrophysics Data System (ADS)

    Larnier, Hugo; Sailhac, Pascal; Chambodut, Aude

    2016-04-01

    Magnetotelluric (MT) data consist of the sum of several types of natural sources including transient and quasiperiodic signals and noise sources (instrumental, anthropogenic) whose nature has to be taken into account in MT data processing. Most processing techniques are based on a Fourier transform of MT time series, and robust statistics at a fixed frequency are used to compute the MT response functions, but only a few take into account the nature of the sources. Moreover, to reduce the influence of noise in the inversion of the response functions, one often sets up another MT station called a remote station. However, even careful setup of this remote station cannot prevent its failure in some cases. Here, we propose the use of the continuous wavelet transform on magnetotelluric time series to reduce the influence of noise even for single site processing. We use two different types of wavelets, Cauchy and Morlet, according to the shape of observed geomagnetic events. We show that by using wavelet coefficients at clearly identified geomagnetic events, we are able to recover the unbiased response function obtained through robust remote processing algorithms. This makes it possible to process even single station sites and increase the confidence in data interpretation.

  13. 3-D Magnetotelluric Exploration of Tenerife Geothermal System (Canary Islands, Spain)

    NASA Astrophysics Data System (ADS)

    Piña-Varas, P.; Ledo, J.; Queralt, P.; Marcuello, A.; Bellmunt, F.; Hidalgo, R.; Messeiller, M.

    2014-07-01

    The resistivity structure of the Tenerife geothermal system has been determined by the 3-D inversion of data from different magnetotelluric surveys. In this paper, the ocean and topography effects on the magnetotelluric data were investigated by constructing a 3-D conceptual geoelectrical model of the island. The study showed that these effects should be taken into account in order to obtain a reliable subsurface model of the island. Data from 148 sites were used during three-dimensional inversion. The most interesting feature in the final geoelectrical model of the geothermal system is a low resistivity structure (<10 Ωm) above the resistive core of the system. The low resistivity structure has been interpreted as a hydrothermal clay alteration cap typically generated in the conventional geothermal systems. The resistivity model has been correlated with a recent seismic velocity model, showing that a low resistivity structure surrounds an area with high P wave velocity and medium-high resistivity. This medium-high resistivity area can be associated with a slowly solidified magma and, therefore, with a hotter part of the geothermal system.

  14. Water exploration using Magnetotelluric and gravity data analysis; Wadi Nisah, Riyadh, Saudi Arabia

    NASA Astrophysics Data System (ADS)

    Aboud, Essam; Saud, Ramzi; Asch, Theodore; Aldamegh, Khaled; Mogren, Saad

    2014-12-01

    Saudi Arabia is a desert country with no permanent rivers or lakes and very little rainfall. Ground water aquifers are the major source of water in Saudi Arabia. In the Riyadh region, several Wadies including Wadi Nisah store about 14 × 106 m3 of water, which is extracted for local irrigation purposes. In such areas, the water wells are as shallow as 200-300 m in depth. The importance of Wadi Nisah is because the subsurface water aquifers that are present there could support the region for many years as a water resource. Accordingly, in this study, we performed a Magnetotelluric survey using a portable broadband sounding system (MT24/LF) to evaluate the ground water aquifer at great depths. We collected 10 broadband Magnetotelluric sounding stations (1 station/day) with an interval of about 2-3 km reaching a profile length of about 25-30 km along Wadi Nisah. Additionally, we used available gravity data to image the subsurface structure containing the aquifer. MT results indicated a low resistivity layer, associated with alluvium deposits, which was defined at a depth of about 1-2 km and extended horizontally about 15 km. Gravity data analysis was used to model this resistivity layer indicating a basement surface at 3-4 km depth.

  15. Magnetotelluric Data, Rainier Mesa/Shoshone Mountain, Nevada Test Site, Nevada

    USGS Publications Warehouse

    Williams, Jackie M.; Sampson, Jay A.; Rodriguez, Brian D.; Asch, Theodore H.

    2006-01-01

    Introduction: The United States Department of Energy (DOE) and the National Nuclear Security Administration (NNSA) at their Nevada Site Office (NSO) are addressing ground-water contamination resulting from historical underground nuclear testing through the Environmental Management (EM) program and, in particular, the Underground Test Area (UGTA) project. During 2005, the U.S. Geological Survey (USGS), in cooperation with the DOE and NNSA-NSO, collected and processed data from twenty-six magnetotelluric (MT) and audio-magnetotelluric (AMT) sites at the Nevada Test Site. The 2005 data stations were located on and near Rainier Mesa and Shoshone Mountain to assist in characterizing the pre-Tertiary geology in those areas. These new stations extend the area of the hydrogeologic study previously conducted in Yucca Flat. The MT data presented in this report will help refine what is known about the character, thickness, and lateral extent of pre Tertiary confining units. Subsequent interpretation will include a three dimensional (3 D) character analysis and a two-dimensional (2 D) resistivity model. The purpose of this report is to release the MT sounding data. No interpretation of the data is included here.

  16. Crustal rheology of the Himalaya and Southern Tibet inferred from magnetotelluric data

    USGS Publications Warehouse

    Unsworth, M.J.; Jones, A.G.; Wei, W.; Marquis, G.; Gokarn, S.G.; Spratt, J.E.; Bedrosian, P.; Booker, J.; Leshou, C.; Clarke, G.; Shenghui, L.; Chanhong, L.; Ming, D.; Sheng, J.; Solon, K.; Handong, T.; Ledo, J.; Roberts, B.

    2005-01-01

    The Cenozoic collision between the Indian and Asian continents formed the Tibetan plateau, beginning about 70 million years ago. Since this time, at least 1,400 km of convergence has been accommodated by a combination of underthrusting of Indian and Asian lithosphere, crustal shortening, horizontal extrusion and lithospheric delamination. Rocks exposed in the Himalaya show evidence of crustal melting and are thought to have been exhumed by rapid erosion and climatically forced crustal flow. Magnetotelluric data can be used to image subsurface electrical resistivity, a parameter sensitive to the presence of interconnected fluids in the host rock matrix, even at low volume fractions. Here we present magnetotelluric data from the Tibetan-Himalayan orogen from 77??E to 92??E, which show that low resistivity, interpreted as a partially molten layer, is present along at least 1,000 km of the southern margin of the Tibetan plateau. The inferred low viscosity of this layer is consistent with the development of climatically forced crustal flow in Southern Tibet. ?? 2005 Nature Publishing Group.

  17. Finite Element Modeling of the Magnetotelluric Phase Tensor Response to Evaluate Sensitivity to Lateral and Vertical Resistivity Contrasts

    NASA Astrophysics Data System (ADS)

    Hawkes, S.; McClain, J. S.

    2015-12-01

    Phase tensor analysis of magnetotelluric data is a relatively new technique introduced by Caldwell et. al. (2004) and requires substantial research efforts to evaluate the capabilities of the method. We have conducted finite element (FE) modeling using the AC/DC module of Comsol Multiphysics to determine the effect of resistivity structure on the phase tensor response. Measurements are made at eleven frequencies from 10-104 Hz at points on a 5x5 grid above various simple model geometries. Phase tensor plotting methods are adapted from Booker (2013) and involve displaying data graphically as stacks of colored ellipses. This allows for interpretation across the frequency spectrum vertically as well as laterally between stations. Two types of plot are presented for each model, a "ϕmin plot" where the ellipses are colored according to the minimum principle phase and a "delta plot" where the ellipses are colored according to the difference between the principle phases (ϕmax - ϕmin), which provides a quantification of the phase anisotropy. Results suggest that the principle phases ϕmin and ϕmax are sensitive to vertical resistivity contrasts but not lateral resistivity contrasts. Conversely, delta plots reveal sensitivity to lateral resistivity contrasts but not vertical resistivity contrasts. A clear distance relationship is observed with proximity to the boundary controlling the frequency range that senses a lateral resistivity contrast. Rotation of the phase tensor ellipses and increased skew values occur in the presence of resistivity contrasts that strike nonparallel to the source field, with the effect increasing towards lower frequencies. The total phase tensor response is confirmed to be sensitive to both vertical and lateral resistivity contrasts and can be used effectively to interpret subsurface resistivity structure.

  18. Magnetotelluric survey for exploration of a volcanic-rock reservoir in the Yurihara oil and gas field, Japan

    SciTech Connect

    Mitsuhata, Yuji; Matsuo, Koichi; Minegishi, Masato

    1999-03-01

    The Yurihara oil and gas field is located on the southern edge of Akita Prefecture, northeastern Japan. In this area, drilling, surface geological surveys and many seismic surveys have been used to investigate the geological structure. Wells drilled into the Nishikurosawa Basalt Group (NBG) of Miocene age found oil and gas reservoirs at depths of 1.5--2 km. Oil and gas are now being produced commercially and further exploration is required in the surrounding areas. However, since the neighboring areas are covered with young volcanic products from the Chokai volcano, and have a rough topography, the subsurface distribution of the NBG must be investigated using other methods in addition to seismic reflection. According to the well data, the resistivity of the NBG is comparatively higher than that of the overlying sedimentary formations, and therefore the magnetotelluric (MT) method is expected to be useful for the estimation of the distribution of the NBG. An MT survey was conducted along three survey lines in this area. Each line trended east-west, perpendicular to the regional geological strike, and was composed of about 25 measurement sites. Induction vectors evaluated from the magnetic field show that this area has a two-dimensional structure. The evaluated resistivity sections are in agreement with the log data. In conclusion, the authors were able to detect resistive layers (the NBG) below conductive layers. The results indicate that the NBG becomes gradually less resistive from north to south. In the center of the northern line, an uplifted resistive area is interpreted as corresponding to the reservoir. By comparison with a seismic section, the authors prove the effectiveness of the integration of seismic and MT surveys for the investigation of the morphology and internal structure of the NBG. On other survey lines, the resistive uplifted zones are interpreted as possible prospective areas.

  19. A new co-operative inversion strategy via fuzzy clustering technique applied to seismic and magnetotelluric data

    NASA Astrophysics Data System (ADS)

    Thong Kieu, Duy; Kepic, Anton

    2015-04-01

    Geophysical inversion produces very useful images of earth parameters; however, inversion results usually suffer from inherent non-uniqueness: many subsurface models with different structures and parameters can explain the measurements. To reduce the ambiguity, extra information about the earth's structure and physical properties is needed. This prior information can be extracted from geological principles, prior petrophysical information from well logs, and complementary information from other geophysical methods. Any technique used to constrain inversion should be able to integrate the prior information and to guide updating inversion process in terms of the geological model. In this research, we have adopted fuzzy c-means (FCM) clustering technique for this purpose. FCM is a clustering method that allows us to divide the model of physical parameters into a few clusters of representative values that also may relate to geological units based on the similarity of the geophysical properties. This exploits the fact that in many geological environments the earth is comprised of a few distinctive rock units with different physical properties. Therefore FCM can provide a platform to constrain geophysical inversion, and should tend to produce models that are geologically meaningful. FCM was incorporated in both separate and co-operative inversion processing of seismic and magnetotelluric (MT) data with petrophysical constraints. Using petrophysical information through FCM assists the inversion to build a reliable earth model. In this algorithm, FCM plays a role of guider; it uses the prior information to drive the model update process, and also forming an earth model filled with rocks units rather than smooth transitions when the boundary is in doubt. Where petrophysical information from well logs or core measurement is not locally available the cluster petrophysics may be solved for in inversion as well if some knowledge of how many distinctive geological exist. A

  20. Magnetotelluric characterization of a tectonic boundary in the Chaco-Pampean Plain (27° S), Argentina

    NASA Astrophysics Data System (ADS)

    Peri, V. G.; Pomposiello, C.; Favetto, A.; Barcelona, H.; Rossello, E.

    2013-05-01

    The study area is placed in the Chaco-Pampean Plain (Central-North Argentina), which is part of the distal plain of the central Andean piedmont originated by the uplift and erosion of the Andean Cordillera. A sedimentary aggradational process typifies this region and buries a large history related to Western Gondwana and Andean Orogeny. The Andean piedmont is composed of a collage of crustal blocks that were amalgamated by different orogeny and deformation belts. The Transbrasiliano lineament constitutes one of these continental belts and transversely intersects the South American Platform, from NNE to SSW. Northward, this lineament is well evidenced, while southward, in the distal Andean foreland, it remains unknown and is associated with the tectonic boundary between the Río de la Plata Craton (RPC) and the Pampean terrane (PT). This tectonic boundary is mostly unexposed in the Chaco-Pampean Plain. An east or west dipping subduction and a later collision between these terranes is still under debate. Deep geophysical studies are not abundant in this region. Few works have locally characterized the composition and structure of the crust and upper mantle beneath this extensive intracontinental plain. Magnetotelluric (MT), gravimetric and magnetic data have inferred the boundary between the RPC and the PT at the limit between Eastern Pampean Ranges and the Chaco-Pampean Plain. Furthermore, at regional scale, 3-D seismic tomographies and images of the seismic structure of the crust and the uppermost mantle have revealed the Moho depths and other lithospheric discontinuities. Here, we report the results of a MT survey along a W-E profile located at 27° S between 63°45' and 60°30' W, that characterized the geoelectric structure of the tectonic boundary between the RPC and the PT beneath the Chaco-Pampean Plain. The MT method provides an image of the electrical resistivity distribution of the Earth's subsurface and constitutes an effective and complementary technique

  1. Simulation of magnetotelluric fields at Stromboli volcano using unstructured grid finite element techniques together with digital topography and bathymetry data

    NASA Astrophysics Data System (ADS)

    Kütter, Sissy; Franke-Börner, Antje; Börner, Ralph-Uwe; Spitzer, Klaus

    2010-05-01

    Marine volcanoes are particularly demanding when it comes to applying electric or electromagnetic methods to investigate their interiors. First, the surrounding highly conductive sea water represents a significant difference in conductivity with respect to the volcanic edifice, second, the volcano's topography has great impact on the electromagnetic response, and, third, the surrounding sea bed topography heavily distorts electromagnetic fields in frequency bands that interfere with a certain spatial wavelength and amplitude of the bathymetry. By neglecting these issues severe misinterpretations are the inevitable consequence. We present different approaches to 3D vector finite element simulation on unstructured grids which are able to compute plain-wave magnetotelluric fields for models including arbitrary surface and sea bed topography. As an example, we consider Stromboli volcano. One major issue is the incorporation of the Stromboli topography using a digital terrain model so that nearly all geometric features affecting the electromagnetic response are considered and an electromagnetic view on Stromboli's interior becomes possible. By carrying out a number of different synthetic experiments it has become obvious that not only the topography of Stromboli island itself is influencing the behavior of the fields but, even stronger, the topography of the surrounding sea bed within a radius of several tens of kilometers. The experiment therefore comprises three steps which gradually approach the complex setting of the target and map the entire volcanic environment with increasing accuracy. The first step outlines the volcano as a resistive geometric frustum surrounded by conductive sea water and underlain by a resistive substratum. This model already gives fundamental answers concerning the principal frequency-dependent current flow pattern within the edifice and the surrounding sea. For this purpose, the MT response was calculated at the earth/sea and the earth

  2. High-resolution magnetotelluric studies of the Archaean-Proterozoic border zone in the Fennoscandian Shield, Finland

    NASA Astrophysics Data System (ADS)

    Vaittinen, K.; Korja, T.; Kaikkonen, P.; Lahti, I.; Smirnov, M. Yu.

    2012-03-01

    The Archaean-Proterozoic collisional zone is a complex mixture of the Archaean complexes [e.g. Iisalmi Complex (IC)], Proterozoic supracrustal belts [e.g. Kainuu Belt (KB) and Savo Belt (SB)] and oceanic arc lithologies in the central Fennoscandian Shield. The zone was formed in the Savo orogeny when the Keitele microcontinent collided with the Archaean Karelian craton in the Palaeoproterozoic time. The crustal architecture of this palaeosuture is studied using new broad-band magnetotelluric data from 104 sites. 2-D conductivity models across the border zone between the Palaeoproterozoic Svecofennian Domain and the Archaean Karelian province are constrained using the recent, partly collocated reflection seismic data from the Finnish Reflection Experiment (FIRE). Dimensionality analyses, in particular the Q-function analysis, show that magnetotelluric data represent reasonably well regional 2-D structure at periods <100 s, which is the longest period used in this study. Strike determinations gave a stable strike of N15W. For the inversions, the data are projected into three parallel profiles with an azimuth of N75E. The determinant inversion is selected as the most suitable method for the data set. Especially the phase data are useable only from the determinant since one of the polarizations have the out-of-quadrant phase at several sites. The interpreted final, geological more appropriate models, where smoother thick conductive areas are replaced by thinner layers, are constructed from the results of the unconstrained smooth inversions with the help of forward modelling, synthetic and prior model inversions and reflection seismic models. The two major sets of crustal conductors are identified. They have an opposite dip and together they form a bowl-shaped conductor. In the west, the eastward dipping SB conductors are located at the bottom of the formation underlain by the Keitele microcontinent. The SB conductors extend to the east possibly cutting the westward

  3. A new methodology to estimate magnetotelluric (MT) tensor relationships: Estimation of Local transfer-functIons by Combining Interstation Transfer-functions (ELICIT)

    NASA Astrophysics Data System (ADS)

    Campanyà, Joan; Ledo, Juanjo; Queralt, Pilar; Marcuello, Alex; Jones, Alan G.

    2014-07-01

    A new methodology to estimate magnetotelluric (MT) tensor relationships, called Estimation of Local transfer-functIons by Combining Interstation Transfer-functions (ELICIT), is proposed whereby the MT tensor relationships of the local site are derived using only interstation transfer functions. The MT impedance tensor and the geomagnetic transfer function at the local site are characterised by combining interstation tensor relationships between electric and magnetic fields at the local site with the horizontal magnetic fields acquired at a neighbouring site. The main property of the proposed method is that the employed interstation transfer functions are independently constrained, without the need to acquire the electric and the magnetic fields at the local site simultaneously to recover the local MT tensor relationships. Due to this property, the ELICIT method offers new possibilities for MT data acquisition and processing, providing significant improvements when the magnetic time-series at the local site are affected by local noise or are truncated. Error analysis shows that, even when magnetic fields are truncated, the quality of the results obtained following the ELICIT method are similar to those we would obtain if the magnetic fields had not been truncated. Another important property is that different neighbouring sites can be used to recover the tensor relationships at the local site. Averaging of results obtained using different neighbouring sites can be performed to improve the statistics. For our example data, when the ELICIT method is used to improve the statistics, errors of the estimates for periods between 1000 and 20 000 s periodicities are clearly reduced. All interstation transfer functions are calculated doing remote reference and the bootstrap method is used to compute the errors, when necessary. Long period magnetotelluric data acquired in the Pyrenees and in the Atlas Mountains in Morocco, and magnetic data provided by F

  4. Lithospheric structures and Precambrian terrane boundaries in northeastern Botswana revealed through magnetotelluric profiling as part of the Southern African Magnetotelluric Experiment

    NASA Astrophysics Data System (ADS)

    Miensopust, M. P.; Jones, A. G.; Muller, M. R.; Garcia, X.; Evans, R. L.

    2011-02-01

    Within the framework of the Southern African Magnetotelluric Experiment a focused study was undertaken to gain improved knowledge of the lithospheric geometries and structures of the westerly extension of the Zimbabwe craton (ZIM) into Botswana, with the overarching aim of increasing our understanding of southern African tectonics. The area of interest is located in northeastern Botswana, where Kalahari sands cover most of the geological terranes and very little is known about lithospheric structures and thicknesses. Some of the regional-scale terrane boundary locations, defined based on potential field data, are not sufficiently accurate for local-scale studies. Investigation of the NNW-SSE orientated, 600 km long ZIM line profile crossing the Zimbabwe craton, Magondi mobile belt, and Ghanzi-Chobe belt showed that the Zimbabwe craton is characterized by thick (˜220 km) resistive lithosphere, consistent with geochemical and geothermal estimates from kimberlite samples of the nearby Orapa and Letlhakane pipes (˜175 km west of the profile). The lithospheric mantle of the Ghanzi-Chobe belt is resistive, but its lithosphere is only about 180 km thick. At crustal depths a northward dipping boundary between the Ghanzi-Chobe and the Magondi belts is identified, and two middle to lower crustal conductors are discovered in the Magondi belt. The crustal terrane boundary between the Magondi and Ghanzi-Chobe belts is found to be located further to the north, and the southwestern boundary of the Zimbabwe craton might be further to the west, than previously inferred from the regional potential field data.

  5. Two and three dimensional magnetotelluric inversion. Final report

    SciTech Connect

    Booker, J.

    1993-05-01

    Electrical conductivity depends on properties such as the presence of ionic fluids in interconnected pores that are difficult to sense with other remote sensing techniques. Thus improved imaging of underground electrical structure has wide practical importance in exploring for groundwater, mineral and geothermal resources, and in assessing the diffusion of fluids in oil fields and waste sites. Because the electromagnetic inverse problem is fundamentally multi-dimensional, most imaging algorithms saturate available computer power long before they can deal with the complete data set. We have developed an algorithm to directly invert large multi-dimensional data sets that is orders of magnitude faster than competing methods. We have proven that a two-dimensional (2D) version of the algorithm is highly effective for real data and have made substantial progress towards a three-dimensional (3D) version. We are proposing to cure identified shortcomings and substantially expand the utility of the existing 2D program, overcome identified difficulties with extending our method to three-dimensions (3D) and embark on an investigation of related EM imaging techniques which may have the potential for even further increasing resolution.

  6. Thermal regimes of major volcanic centers: magnetotelluric constraints

    SciTech Connect

    Hermance, J.F.

    1987-11-13

    The focus of activity at this laboratory is on applying natural electromagnetic methods along with other geophysical techniques to studying the dynamical processes and thermal regimes associated with centers of major volcanic activity. We are presently emphasizing studies of the Long Valley/Mono Craters Volcanic Complex, the Cascades Volcanic Belt, and the Valles Caldera. This work addresses questions regarding geothermal energy, chemical transport of minerals in the crust, emplacement of economic ore deposits, and optimal siting of drill-holes for scientific purposes. In addition, since much of our work is performed in the intermontane sedimentary basins of the western US (along with testing our field-system in some of the graben structures in the Northeast), there is an application of these studies to developing exploration and interpretational strategies for detecting and delineating structures associated with hydrocarbon reserves.

  7. Magnetotelluric/audiomagnetotelluric study of the Zuni Hot Dry Rock Geothermal Prospect, New Mexico

    SciTech Connect

    Ander, M.E.; Goss, R.; Strangway, D.; Hillebrand, C.; Laughlin, A.W.; Hudson, C.

    1980-01-01

    The Los Alamos Scientific Laboratory has been investigating a large area in New Mexico for Hot Dry Rock geothermal potential. The area includes parts of the Jemez volcanic lineament and the central Rio Grande rift. LASL has completed a detailed magnetotelluric/audiomagnetotelluric survey covering 161 square km over an area of high heat flow, south of Zuni, NM. The data collection was collected and preliminary analysis phases of a regional MT survey which suggest the Jemez lineament is associated with a crustal structure of anomalously high electrical conductivity. The detailed MT shows an average tipper strike of N60/sup 0/E above 100 sec period, representing the structural trend within Precambrian basement. The Jemez lineament strikes approximately N55/sup 0/E; this suggests a relationship between the Precambrian structure beneath the Zuni area and the Jemez lineament.

  8. Crustal structure of the Chicxulub Impact crater imaged with magnetotelluric exploration

    NASA Astrophysics Data System (ADS)

    Unsworth, Martyn; Enriquez, Oscar Campos; Belmonte, Salvador; Arzate, Jorge; Bedrosian, Paul

    2002-08-01

    The electrical resistivity structure of the Chicxulub Impact crater has been imaged using broadband magnetotelluric exploration. A 1-2 km thick sequence of conductive Tertiary sedimentary rocks was imaged within the crater. The shallow resistivity of this layer increases across the cenote ring. This is primarily due to a decrease in porosity, although the groundwater composition may have some effect. While this layer reduces the sensitivity of MT, several features can be discerned beneath it. In the center of the crater the structural high is imaged as a region of high resistivity. In the outer part of the crater, lower resistivities in the upper crust may be due to mineralization or hydrothermal alteration.

  9. Seismic and magneto-telluric imaging for geothermal exploration at Jemez pueblo in New Mexico

    SciTech Connect

    Huang, Lianjie; Albrecht, Michael

    2011-01-25

    A shallow geothermal reservoir in the Pueblo of Jemez in New Mexico may indicate a commercial-scale geothermal energy potential in the area. To explore the geothermal resource at Jemez Pueblo, seismic surveys are conducted along three lines for the purpose of imaging complex subsurface structures near the Indian Springs fault zone. A 3-D magneto-telluric (MT) survey is also carried out in the same area. Seismic and MT imaging can provide complementary information to reveal detailed geologic formation properties around the fault zones. The high-resolution seismic images will be used together with MT images, geologic mapping, and hydrogeochemistry, to explore the geothermal resource at Jemez Pueblo, and to determine whether a conunercial-scale geothermal resource exists for power generation or direct use applications after drilling and well testing.

  10. Electrical resistivity image of the South Atlantic continental margin derived from onshore and offshore magnetotelluric data

    NASA Astrophysics Data System (ADS)

    Kapinos, G.; Weckmann, U.; Jegen-Kulcsar, M.; Meqbel, N.; Neska, A.; Katjiuongua, T. T.; Hoelz, S.; Ritter, O.

    2016-01-01

    We present a deep electrical resistivity image from the passive continental margin in Namibia. The approximately 700 km long magnetotelluric profile follows the Walvis Ridge offshore, continues onshore across the Kaoko Mobile Belt and reaches onto the Congo Craton. Two-dimensional inversion reveals moderately resistive material offshore, atypically low for oceanic lithosphere, reaching depths of 15-20 km. Such moderate resistivities are consistent with seismic P wave velocity models, which suggest up to 35 km thick crust. The Neoproterozoic rocks of the Kaoko Mobile Belt are resistive, but NNW-striking major shear-zones are imaged as subvertical, conductive structures in the upper and middle crust. Since the geophysical imprint of the shear zones is intact, opening of the South Atlantic in the Cretaceous did not alter the middle crust. The transition into the cratonic region coincides with a deepening of the high-resistive material to depths of more than 60 km.