# Remote reference magnetotelluric impedance estimation of wideband data using hybrid algorithm

TL;DR: In this article, the results of hybrid processing schemes in conjunction with the remote reference (RR) for a typical site out of several sites collected over the wide band data (∼103 to 10−3 Hz).

Abstract: [1] Precise and accurate determination of the magnetotelluric (MT) impedance is fundamental to valid interpretation. This paper deals with the results of hybrid processing schemes in conjunction with the remote reference (RR), for a typical site out of several sites collected over the wide band data (∼103 to 10−3 Hz). The standard practice of MT impedance estimation is the use of robust processing in conjunction with the remote referencing. The estimation by robust technique helps in reducing the effect of outliers in the electric field but is often not sensitive to the exceptional predictor (magnetic field) data, which are called leverage points. The data processed with robust M estimation (RME) exacerbated the bias problem in the dead band. The application of hybrid (coherence weighted estimation (CWE) + RME, rho-variance weighting + RME) and extra hybrid (CWE + rho variance + RME) approach helps in reducing the influence of both the outliers in the electric field and the leverage points. These two approaches perform considerably better than either data weighting scheme by itself.

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TL;DR: In this article, the authors reported thickness of the LAB in one of the oldest dated ancient cratons of India, Eastern Indian Craton (EIC) of ~ 3.3 Gyr, from magnetotelluric (MT) observations.

53 citations

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TL;DR: In this paper, a 2D inversion using TE+++TM and TE+TM+Tzy inversion brings up two conducting zones enveloping three anomalous conducting bodies.

15 citations

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TL;DR: In this paper, the authors conducted 14 audio-magnetotelluric (AMT) measurements for a profile of about 20 km in the frequency range of 1 kHz to 10 Hz over this rather complex geologic environment covering Dhanjori Volcanics (DhV) and Kolhan Group (KG).

Abstract: Greenstone belts are well known for gold occurrences at different regions of the world. The Dhanjori basin in the eastern Singhbhum region shows major characteristics of a rifted greenstone belt. Initially, we conducted 14 audio-magnetotelluric (AMT) measurements for a profile of $$\sim $$
20 km in the frequency range of 1 kHz to 10 Hz over this rather complex geologic environment covering Dhanjori Volcanics (DhV) and Kolhan Group (KG). Subsequently, gravity and magnetic surveys were also conducted over this AMT profile. The purpose of the survey was to identify and map conductive features and to relate them to metallogeny of the area along with the mapping of the basement of Dhanjori basin. The strike analysis showed $$\hbox {N30}^{\circ }\hbox {W}$$
strike for DhV for all the frequencies and for sites over KG domain in the frequency range of 100–10 Hz, but for KG domain, the obtained strike in 1 kHz to 100 Hz is $$\hbox {N45}^{\circ }\hbox {E}$$
. As the combination of transverse electric (TE), transverse magnetic (TM) and tipper (Tzy) can recover the electrical signature in complex geological environment, we discuss the conductivity model obtained from TE+TM+Tzy only. The inversion was carried for the regional profile with 14 sites and for 7 sites over KG domain. Conductivity model shows two well resolved conductors, one each in KG and Quartz Pebble Conglomerate Dhanjori (QPCD) domains respectively showing common linked concordant features between these regional and KG profiles. The conductors are interpreted as sulfide mineralization linked with QPCD group of rocks which may host gold. These conductors are also horizontally disposed due to the intrusive younger Mayurbhanj Granite. These intrusives correlate well with the gravity modeling as well. The thickness of the Dhanjori basin at the central is about 3.0 km, similar to that from gravity modeling. The conductivity model also indicates the presence of shallow conductors, but could not be resolved due to lack of high frequency data. However, the results from the close-by drill site indicate the presence of shallow sulfide mineralization hosting gold. The deep level conductors delineated from AMT studies are associated with gravity high and low magnetic. ICP-AES results of Dhanjori samples show significant concentration of gold $$\sim $$
5.0 g/t, which is of economic consideration. Thus, it can be inferred that the conductors have evidences of sulfide mineralization which host gold.

12 citations

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TL;DR: In this article, a 3D inversion of off-diagonal component of impedance was performed for obtaining an optimum value of uniform half space initial resistivity and error floor for offdiagonal components of impedance data.

11 citations

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8 citations

##### References

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01 Jan 1987

TL;DR: This paper presents the results of a two-year study of the statistical treatment of outliers in the context of one-Dimensional Location and its applications to discrete-time reinforcement learning.

Abstract: 1. Introduction. 2. Simple Regression. 3. Multiple Regression. 4. The Special Case of One-Dimensional Location. 5. Algorithms. 6. Outlier Diagnostics. 7. Related Statistical Techniques. References. Table of Data Sets. Index.

6,955 citations

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28 Jan 2005

3,532 citations

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TL;DR: In this article, magnetic field measurements were performed simultaneously at two sites 4.8 km apart near Hollister, California, where the data obtained at each site were analyzed using the magnetic fields at the other site as a remote reference.

Abstract: Magnetotelluric measurements were performed simultaneously at two sites 4.8 km apart near Hollister, California. SQUID magnetometers were used to measure fluctuations in two orthogonal horizontal components of the magnetic field. The data obtained at each site were analyzed using the magnetic fields at the other site as a remote reference. In this technique, one mUltiplies the equations relating the Fourier components of the electric and magnetic fields by a component of magnetic field from the remote reference. By averaging the various crossproducts, one can obtain estimates of the impedance tensor that are unbiased by noise, provided there are no correlations between the noises in the remote channels and the noises in the local channels. Even for data for which the E-E predicted coherencies were as low as 0.1, the apparent resistivities obtained from this technique were consistent with apparent resistivities calculated from high coherency data at adjacent periods. Apparent resistivities calculated by conventional analysis of the same data were biased by as much as two orders of magnitude. The estimated standard deviation for periods shorter than 3 s was less than 5%, and, for 87% of the data, was less than 2%. Where data bands overlapped between periods of 0.33more » s and 1 s,the average discrepancy between the apparent resistivities was 1.8%.« less

695 citations