Prediction of silicate melt viscosity from electrical conductivity : a model and its geophysical implications

Author Posting. © American Geophysical Union, 2013. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geochemistry, Geophysics, Geosystems 14 (2013): 1685–1692, doi:10.1002/ggge.20103.Our knowledge of magma dynamics would be improved if geophysical data could be used to infer rheological constraints in melt-bearing zones. Geophysical images of the Earth's interior provide frozen snapshots of a dynamical system. However, knowledge of a rheological parameter such as viscosity would constrain the time-dependent dynamics of melt bearing zones. We propose a model that relates melt viscosity to electrical conductivity for naturally occurring melt compositions (including H2O) and temperature. Based on laboratory measurements of melt conductivity and viscosity, our model provides a rheological dimension to the interpretation of electromagnetic anomalies caused by melt and partially molten rocks (melt fraction ~ >0.7).We acknowledge partial support under NASA USRA subaward 02153–04, NSF EAR 0739050, and the ASU School of Earth and Space Exploration (SESE) Exploration Postdoctoral Fellowship Program.2013-12-1

UNICEF IWASH Project, Northern Region, Ghana : an adapted training manual for groundwater development

This report is an adapted training manual, with specific best practice recommendations for groundwater development practitioners working in the Northern Region, Ghana. It is designed to be used in conjunction with the existing comprehensive training manual ‘Developing Groundwater: a guide to rural water supply’ by MacDonald, Davies, Calow and Chilton (2005). The additional guidelines provided in this supplementary report are specific to the Northern Region of Ghana, and have been informed by a review of groundwater development in the region which BGS carried out on behalf of UNICEF in 2010-2011. The Northern Region is a difficult area in which to find and develop groundwater resources. For this reason, more resources – time and money – need to be focussed on careful borehole siting and development in order to maximise success. This includes detailed desk and field reconnaissance surveys; the effective use and interpretation of geophysical siting methods; collection of good quality data during drilling and test pumping; rigorous recording and management of data; and effective interpretation, sharing and use of hydrogeological information by all groundwater development practitioners. This report, and the associated manual ‘Developing Groundwater’, provide practical help for carrying out these activities effectively. The authors gratefully acknowledge those persons who contributed to the formation of these guidelines, who include: UNICEF Ghana – Othniel Habila, Kabuka Banda and David Ede Community Water and Sanitation Agency (CWSA), Ghana – John Aduakye Canadian International Development Agency (CIDA) – Hydrogeological Assessment Project (HAP) – James Racicot All participants at the UNICEF/BGS workshop and training programme held in Tamale, Northern Region, from 7 to 18 February 2011

Geophysical Applications for Arctic/Subarctic Transportation Planning

This report describes a series of geophysical surveys conducted in conjunction with geotechnical investigations carried out by the Alaska Department of Transportation and Public Facilities. The purpose of the study was to evaluate the value of and potential uses for data collected via geophysical techniques with respect to ongoing investigations related to linear infrastructure. One or more techniques, including direct-current resistivity, capacitive-coupled resistivity, and ground-penetrating radar, were evaluated at sites in continuous and discontinuous permafrost zones. Results revealed that resistivity techniques adequately differentiate between frozen and unfrozen ground, and in some instances, were able to identify individual ice wedges in a frozen heterogeneous matrix. Capacitive-coupled resistivity was found to be extremely promising due to its relative mobility as compared with direct-current resistivity. Ground-penetrating radar was shown to be useful for evaluating the factors leading to subsidence in an existing road. Taken as a whole, the study results indicate that supplemental geophysical surveys may add to the quality of a geotechnical investigation by helping to optimize the placement of boreholes. Moreover, such surveys may reduce the overall investigation costs by reducing the number of boreholes required to characterize the subsurface

Empiric Models of the Earth's Free Core Nutation

Free core nutation (FCN) is the main factor that limits the accuracy of the modeling of the motion of Earth's rotational axis in the celestial coordinate system. Several FCN models have been proposed. A comparative analysis is made of the known models including the model proposed by the author. The use of the FCN model is shown to substantially increase the accuracy of the modeling of Earth's rotation. Furthermore, the FCN component extracted from the observed motion of Earth's rotational axis is an important source for the study of the shape and rotation of the Earth's core. A comparison of different FCN models has shown that the proposed model is better than other models if used to extract the geophysical signal (the amplitude and phase of FCN) from observational data.Comment: 8 pages, 3 figures; minor update of the journal published versio

Field-based Research Experience in Earth Science Teacher Education

This is an overview of a field-based research experience in Earth Science teacher education program that was conducted for secondary science teachers from Prince George's County, Maryland. The goal of the program was to produce well-prepared, scientifically and technologically literate Earth Science teachers through a teaching- and research-oriented partnership between in-service teachers and a university scientist-educator. Program participants were exposed to a broad background in field-based instruction in physical, historical, and environmental aspects of Earth Science content and teaching methods, followed by participation in an authentic, technology-rich field research project. Although attrition rates were high, program participants indicated that they were more confident in their Earth Science content knowledge and teaching ability than they had been initially. All respondents also indicated that they were currently using methods, strategies, and activities they had learned in the program within their own classrooms. Educational levels: Graduate or professional

Radio-Echo Sounding Over Polar Ice Masses

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3-D Magnetotelluric Investigations for geothermal exploration in Martinique (Lesser Antilles). Characteristic Deep Resistivity Structures, and Shallow Resistivity Distribution Matching Heliborne TEM Results

Within the framework of a global French program oriented towards the development of renewable energies, Martinique Island (Lesser Antilles, France) has been extensively investigated (from 2012 to 2013) through an integrated multi-methods approach, with the aim to define precisely the potential geothermal ressources, previously highlighted (Sanjuan et al., 2003). Amongst the common investigation methods deployed, we carried out three magnetotelluric (MT) surveys located above three of the most promising geothermal fields of Martinique, namely the Anses d'Arlet, the Montagne Pel{\'e}e and the Pitons du Carbet prospects. A total of about 100 MT stations were acquired showing single or multi-dimensional behaviors and static shift effects. After processing data with remote reference, 3-D MT inversions of the four complex elements of MT impedance tensor without pre-static-shift correction, have been performed for each sector, providing three 3-D resistivity models down to about 12 to 30 km depth. The sea coast effect has been taken into account in the 3-D inversion through generation of a 3-D resistivity model including the bathymetry around Martinique from the coast up to a distance of 200 km. The forward response of the model is used to calculate coast effect coefficients that are applied to the calculated MT response during the 3-D inversion process for comparison with the observed data. 3-D resistivity models of each sector, which are inherited from different geological history, show 3-D resistivity distribution and specificities related to its volcanological history. In particular, the geothermal field related to the Montagne Pel{\'e}e strato-volcano, is characterized by a quasi ubiquitous conductive layer and quite monotonic typical resistivity distribution making interpretation difficult in terms of geothermal targets. At the opposite, the resistivity distribution of Anse d'Arlet area is radically different and geothermal target is thought to be connected to a not so deep resistive intrusion elongated along a main structural axis. Beside these interesting deep structures, we demonstrate, after analyzing the results of the recent heliborne TEM survey covering the whole Martinique, that surface resistivity distribution obtained from 3-D inversion reproduce faithfully the resistivity distribution observed by TEM. In spite of a very different sampling scale, this comparison illustrates the ability of 3-D MT inversion to take into account and reproduce static shift effects in the sub-surface resistivity distribution.Comment: Wordl Geothermal Congress 2015, Apr 2015, Melbourne, Australi

Long-term monitoring of geodynamic surface deformation using SAR interferometry

Thesis (Ph.D.) University of Alaska Fairbanks, 2014Synthetic Aperture Radar Interferometry (InSAR) is a powerful tool to measure surface deformation and is well suited for surveying active volcanoes using historical and existing satellites. However, the value and applicability of InSAR for geodynamic monitoring problems is limited by the influence of temporal decorrelation and electromagnetic path delay variations in the atmosphere, both of which reduce the sensitivity and accuracy of the technique. The aim of this PhD thesis research is: how to optimize the quantity and quality of deformation signals extracted from InSAR stacks that contain only a low number of images in order to facilitate volcano monitoring and the study of their geophysical signatures. In particular, the focus is on methods of mitigating atmospheric artifacts in interferograms by combining time-series InSAR techniques and external atmospheric delay maps derived by Numerical Weather Prediction (NWP) models. In the first chapter of the thesis, the potential of the NWP Weather Research & Forecasting (WRF) model for InSAR data correction has been studied extensively. Forecasted atmospheric delays derived from operational High Resolution Rapid Refresh for the Alaska region (HRRRAK) products have been compared to radiosonding measurements in the first chapter. The result suggests that the HRRR-AK operational products are a good data source for correcting atmospheric delays in spaceborne geodetic radar observations, if the geophysical signal to be observed is larger than 20 mm. In the second chapter, an advanced method for integrating NWP products into the time series InSAR workflow is developed. The efficiency of the algorithm is tested via simulated data experiments, which demonstrate the method outperforms other more conventional methods. In Chapter 3, a geophysical case study is performed by applying the developed algorithm to the active volcanoes of Unimak Island Alaska (Westdahl, Fisher and Shishaldin) for long term volcano deformation monitoring. The volcano source location at Westdahl is determined to be approx. 7 km below sea level and approx. 3.5 km north of the Westdahl peak. This study demonstrates that Fisher caldera has had continuous subsidence over more than 10 years and there is no evident deformation signal around Shishaldin peak.Chapter 1. Performance of the High Resolution Atmospheric Model HRRR-AK for Correcting Geodetic Observations from Spaceborne Radars -- Chapter 2. Robust atmospheric filtering of InSAR data based on numerical weather prediction models -- Chapter 3. Subtle motion long term monitoring of Unimak Island from 2003 to 2010 by advanced time series SAR interferometry -- Chapter 4. Conclusion and future work

The 3D Attenuation Structure of Deception Island (Antarctica)

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