Paul A. Bedrosian

United States Geological Survey

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Anna Kelbert

United States Geological Survey

Jeffrey J. Love

United States Geological Survey

Martyn Unsworth

University of Alberta

U. Weckmann

Helmholtz Centre Potsdam - GFZ German Research Centre for Geosciences

B. J. Minsley

United States Geological Survey

E. J. Rigler

United States Geological Survey

O. Ritter

Helmholtz Centre Potsdam - GFZ German Research Centre for Geosciences

Benjamin S. Murphy

United States Geological Survey

D. W. Feucht

University of Colorado Boulder

Carol A. Finn

United States Geological Survey

Cooperative Institutions

United States Geological Survey

109

John Wiley & Sons (United States)

Helmholtz Centre Potsdam - GFZ German Research Centre for Geosciences

Charles River Laboratories (Netherlands)

Denver Federal Center

Hanover College

United States Department of the Interior

University of Potsdam

Colorado School of Mines

Planetary Science Institute

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A one-dimensional model of solid-earth electrical resistivity beneath Florida

Antarctica A Keystone in a Changing World (2015)

Cletus C. Blum Jeffrey J. Love Kolby Pedrie Paul A. Bedrosian E. J. Rigler

First posted November 19, 2015 For additional information, contact: Director, Geologic Hazards Science Center U.S. Geological Survey Box 25046, MS–966 Denver, CO 80225-0046http://geohazards.cr.usgs.gov/ An estimated one-dimensional layered model of electrical resistivity beneath Florida was developed from published geological and geophysical information. The resistivity of each layer is represented by plausible upper and lower bounds as well as a geometric mean resistivity. Corresponding impedance transfer functions, Schmucker-Weidelt transfer functions, apparent resistivity, and phase responses are calculated for inducing geomagnetic frequencies ranging from 10−5 to 100 hertz. The resulting one-dimensional model and response functions can be used to make general estimates of time-varying electric fields associated with geomagnetic storms such as might represent induction hazards for electric-power grid operation. The plausible upper- and lower-bound resistivity structures show the uncertainty, giving a wide range of plausible time-varying electric fields.

Electrical Resistivity Tomography

10.3133/ofr20151185

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Citations (7)

Hydrothermal circulation at Mount St. Helens determined by self-potential measurements

Journal of Volcanology and Geothermal Research (2006)

Paul A. Bedrosian Martyn Unsworth M. J. S. Johnston

Fumarole

Dome (geology)

Caldera

Lava dome

10.1016/j.jvolgeores.2006.09.003

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Citations (34)

Event list for intense geoelectric fields identified from EarthScope sites during geomagnetic storms

Zenodo (CERN European Organization for Nuclear Research) (2022)

Xueling Shi M. Hartinger J. B. H. Baker Benjamin S. Murphy Paul A. Bedrosian

This data set contains properties of intense geoelectric field events identified from 24 EarthScope sites during geomagnetic storms with Dst minima of less than - 100 nT from 2006 to 2019. Columns are the name of EarthScope site that detected the event (station), geoelectric field component in which the event was detected (Ecomp), the component value of geoelectric fields (Edata), geoelectric field peak prominence, geoelectric field peak width, dBx/dt at the time of the geoelectric field peak, dBy/dt at the time of geoelectric field peak, date and time when the intense geoelectric field peak was observed, geographical latitude of the EarthScope site (glat), geographical longitude of the EarthScope site (glon), geomagnetic latitude of the EarthScope site (mlat), geomagnetic longitude of the EarthScope site (mlon), and magnetic local time of the EarthScope site when the event was detected (mlt).

10.5281/zenodo.6338092

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Lithospheric conductors reveal source regions of convergent margin mineral systems

Scientific Reports (2022)

Alison Kirkby K. Czarnota David L. Huston D.C. Champion Michael P. Doublier

The clean energy transition will require a vast increase in metal supply, yet new mineral deposit discoveries are declining, due in part to challenges associated with exploring under sedimentary and volcanic cover. Recently, several case studies have demonstrated links between lithospheric electrical conductors imaged using magnetotelluric (MT) data and mineral deposits, notably Iron Oxide Copper Gold (IOCG). Adoption of MT methods for exploration is therefore growing but the general applicability and relationship with many other deposit types remains untested. Here, we compile a global inventory of MT resistivity models from Australia, North and South America, and China and undertake the first quantitative assessment of the spatial association between conductors and three mineral deposit types commonly formed in convergent margin settings. We find that deposits formed early in an orogenic cycle such as volcanic hosted massive sulfide (VHMS) and copper porphyry deposits show weak to moderate correlations with conductors in the upper mantle. In contrast, deposits formed later in an orogenic cycle, such as orogenic gold, show strong correlations with mid-crustal conductors. These variations in resistivity response likely reflect mineralogical differences in the metal source regions of these mineral systems and suggest a metamorphic-fluid source for orogenic gold is significant. Our results indicate the resistivity structure of mineralized convergent margins strongly reflects late-stage processes and can be preserved for hundreds of millions of years. Discerning use of MT is therefore a powerful tool for mineral exploration.

Magnetotellurics

10.1038/s41598-022-11921-2

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Analysis of the Magnetotelluric Profile Data from the Española Basin, New Mexico

AGU Fall Meeting Abstracts (2018)

K. Pratscher J. Grab T. Wang R. Chi-Duran D. W. Feucht

Magnetotellurics

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A deep crustal fluid channel into the San Andreas Fault system near Parkfield, California

Geophysical Journal International (2008)

Michael Becken O. Ritter S. K. Park Paul A. Bedrosian U. Weckmann

Magnetotelluric (MT) data from 66 sites along a 45-km-long profile across the San Andreas Fault (SAF) were inverted to obtain the 2-D electrical resistivity structure of the crust near the San Andreas Fault Observatory at Depth (SAFOD). The most intriguing feature of the resistivity model is a steeply dipping upper crustal high-conductivity zone flanking the seismically defined SAF to the NE, that widens into the lower crust and appears to be connected to a broad conductivity anomaly in the upper mantle. Hypothesis tests of the inversion model suggest that upper and lower crustal and upper-mantle anomalies may be interconnected. We speculate that the high conductivities are caused by fluids and may represent a deep-rooted channel for crustal and/or mantle fluid ascent. Based on the chemical analysis of well waters, it was previously suggested that fluids can enter the brittle regime of the SAF system from the lower crust and mantle. At high pressures, these fluids can contribute to fault-weakening at seismogenic depths. These geochemical studies predicted the existence of a deep fluid source and a permeable pathway through the crust. Our resistivity model images a conductive pathway, which penetrates the entire crust, in agreement with the geochemical interpretation. However, the resistivity model also shows that the upper crustal branch of the high-conductivity zone is located NE of the seismically defined SAF, suggesting that the SAF does not itself act as a major fluid pathway. This interpretation is supported by both, the location of the upper crustal high-conductivity zone and recent studies within the SAFOD main hole, which indicate that pore pressures within the core of the SAF zone are not anomalously high, that mantle-derived fluids are minor constituents to the fault-zone fluid composition and that both the volume of mantle fluids and the fluid pressure increase to the NE of the SAF. We further infer from the MT model that the resistive Salinian block basement to the SW of the SAFOD represents an isolated body, being 5–8 km wide and reaching to depths >7 km, in agreement with aeromagnetic data. This body is separated from a massive block of Salinian crust farther to the SW. The NE terminus of resistive Salinian crust has a spatial relationship with a near-vertical zone of increased seismic reflectivity ∼15 km SW of the SAF and likely represents a deep-reaching fault zone.

Magnetotellurics

Upper crust

10.1111/j.1365-246x.2008.03754.x

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Citations (91)

HYDROLOGIC IMPLICATIONS FROM AIRBORNE RESISTIVITY SURVEYS OF THE SAND HILLS OF WESTERN NEBRASKA

Symposium on the Application of Geophysics to Engineering and Environmental Problems 2000 (2013)

Bruce D. Smith James C. Cannia Jared D. Abraham Donald O. Rosenberry Alexander Prikhodko

The Sand Hills of western Nebraska are part of an extensive terrain of dunes distributed across the Great Plains. These dune complexes provide unique ecosystems, recharge to underlying aquifers including the Ogallala aquifer, and are very sensitive to short and longer term climate changes. Understanding the hydrogeologic framework of these dune systems and their underlying aquifers is essential in management of groundwater resources and ecosystems. The hydrogeologic framework is a critical component in understanding implications of climate change for one of the most productive agricultural regions of the United States A frequency domain airborne electromagnetic (AEM) resistivity survey performed in 2010 in the area of Crescent Lakes National Wildlife Refuge (CLNWR) was extended several 10s of kilometers to the north and east with a time domain AEM survey conducted in early 2012. Previous hydrologic studies in the area have demonstrated that a dune dam has blocked the now partially buried Blue Creek. The dune dam is defined by a resistive zone that has a depth of 45 meters suggesting that it influences modern ground-water flow paths and surface-water features. In addition shallow lakes in the immediate area have variable salinity. This difference in salinity appears to be related to the lake interaction with the regional groundwater system. The AEM resistivity depth sections show the subsurface distribution of dune sands and saline waters that act as a natural tracer for groundwater flow. The flow path of the saline waters follow the same patterns as classical groundwater models proposed nearly two decades ago. Some saline waters are perched above more resistive zones that may contain fresher waters. Other conductive zones suggest downward flow from saline lakes. In general flow paths are consistent with previously suggested paleo-channels of the ancestral Blue Creek. Ground-water flow paths controlled by buried topography interpreted from new geophysical surveys are important in predicting how possible deep and shallow groundwater are interconnected.

10.4133/sageep2013-252.1

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

2015 AGU Fall Meeting (2015)

G. Zelenak Kerry Key N. L. Bennington Paul A. Bedrosian

Magnetotellurics

Caldera

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Quantitative Hydrogeological Framework Interpretations from Modeling Helicopter Electromagnetic Survey Data, Nebraska Panhandle

AGU Fall Meeting Abstracts (2009)

Jared D. Abraham Lyndsay B. Ball Paul A. Bedrosian James C. Cannia Maria Deszcz‐Pan

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Evaluating Transient Electromagnetic Data in a High Noise Environment

Symposium on the Application of Geophysics to Engineering and Environmental Problems 2000 (2012)

Daniel Friedman Becky Hollingshaus Benjamin Lee Collin Wilson Paul A. Bedrosian

In 2011, the Summer of Applied Geophysical Experience (SAGE) students acquired transient electromagnetic (TEM) sounding data at 20 sites in the Caja del Rio (CDR) area, west of Santa Fe, New Mexico to assess groundwater conditions and the potential for future geophysical work. The CDR area is reported to have geothermal potential, so TEM data were collected to constrain the structure and water quality of the local aquifer. Unfortunately, the CDR survey area also has multiple noise sources present including a power transmission substation, a series of high‐voltage transmission lines, and gas and water pipelines. It is necessary to assess the impact of the noise sources on TEM data from study areas like the CDR before inverting and interpreting the data. We analyzed the maximum amplitude of background noise relative to the measured transient decay and used the deviation of the sounding response from a power‐law decay to empirically estimate the extent of electromagnetic (EM) coupling to anthropogenic structures at each site along the profile. The theoretical effects of EM coupling as a function of distance were also calculated for an infinite line source. A correlation between potential noise sources and measured background noise was found, but no evidence of EM coupling was observed in the data, which we attribute to the conductive environment and relatively small transmitter loop size. In a more resistive environment the background noise would have been more problematic and a larger transmitter moment would increase coupling with the infrastructure. Our analysis indicates that the TEM data are valid, and for this data set the estimated signal‐to‐noise ratios are sufficient for reliable interpretation of TEM inverse models. The electrical resistivity of the CDR subsurface was modeled to a depth of approximately 150 meters. Results of two‐ and three‐layered one‐dimensional TEM inverse models are in agreement with well‐log data in the CDR area. Porosity variations along the top of the aquifer were not resolvable due to high clay content in the sediments. The results of this study leave room for further investigations of the local aquifer structure and chemistry.

Transient (computer programming)

Geological survey

10.4133/1.4721888

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