5. Electromagnetic Sounding

Spies, Brian R.; Frischknecht, F.C.

doi:10.1190/1.9781560802686.ch5

Cited by 150 publications

(100 citation statements)

References 0 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…In addition to direct monitoring of the geoelectric field, one can estimate the geoelectric field though characterizing and mapping the behavior of the Earth's ground-level geomagnetic field across broad geographic regions (e.g., Love et al 2016) and characterizing an impedance (e.g., Chave 2012) at a given location, which is dependent on the 3-dimensional conductivity distribution of the Earth's interior (e.g., Bedrosian and Feucht 2014;Meqbel et al 2014;Alekseev et al 2015). Subsurface conductivity can also be characterized with active sources, as described in works such as Spies and Frischknecht (1991) on land or Swidinsky et al (2015) in the marine environment; such conductivity models can be used to supplement impedances typically constructed using passive magnetotelluric methods.…”

Section: Introductionmentioning

confidence: 99%

Geoelectric hazard assessment: the differences of geoelectric responses during magnetic storms within common physiographic zones

Cuttler

Love

Swidinsky

2018

Earth Planets Space

View full text Add to dashboard Cite

Geomagnetic field data obtained through the INTERMAGNET program are convolved with with magnetotelluric surface impedance from four EarthScope USArray sites to estimate the geoelectric variations throughout the duration of a magnetic storm. A duration of time from June 22, 2016, to June 25, 2016, is considered which encompasses a magnetic storm of moderate size recorded at the Brandon, Manitoba and Fredericksburg, Virginia magnetic observatories over 3 days. Two impedance sites were chosen in each case which represent different responses while being within close geographic proximity and within the same physiographic zone. This study produces estimated time series of the geoelectric field throughout the duration of a magnetic storm, providing an understanding of how the geoelectric field differs across small geographic distances within the same physiographic zone. This study shows that the geoelectric response of two sites within 200 km of one another can differ by up to two orders of magnitude (4484 mV/km at one site and 41 mV/km at another site 125 km away). This study demonstrates that the application of uniform 1-dimensional conductivity models of the subsurface to wide geographic regions is insufficient to predict the geoelectric hazard at a given site. This necessitates that an evaluation of the 3-dimensional conductivity distribution at a given location is necessary to produce a reliable estimation of how the geoelectric field evolves over the course of a magnetic storm.© The Author(s) 2018. This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.

show abstract

Section: Introductionmentioning

confidence: 99%

Geoelectric hazard assessment: the differences of geoelectric responses during magnetic storms within common physiographic zones

Cuttler

Love

Swidinsky

2018

Earth Planets Space

View full text Add to dashboard Cite

show abstract

“…균질 반무한공간(half space)의 표면에서 단위 수평쌍극자로 생성된 동일선(inline) 수평 step-off 반응의 전기장 e x (t)는 다음 과 같이 주어진다 (Spies and Frischknecht, 1991). ,…”

Section: 하였다unclassified

A Scheme for Computing Time-domain Electromagnetic Fields of a Horizontally Layered Earth

Jang¹,

Kim²

2013

Geophysics and Geophysical Exploration

View full text Add to dashboard Cite

A computer program has been developed to estimate time-domain electromagnetic (EM) responses for a onedimensional model with multiple source and receiver dipoles that are finite in length. The time-domain solution can be obtained by applying an inverse fast Fourier transform (FFT) to frequency-domain fields for efficiency. Frequency-domain responses are first obtained for 10 logarithmically equidistant frequencies per decade, and then cubic spline interpolated to get the FFT input. In the case of phases, the phase curve must be made to be continuous prior to the spline interpolation. The spline interpolated data are convolved with a source current waveform prior to FFT. In this paper, only a step-off waveform is considered. This time-domain code is verified with an analytic solution and EM responses for a marine hydrocarbon reservoir model. Through these comparisons, we can confirm that the accuracy of the developed program is fairly high.

show abstract

“…The SPM decay recorded at 40 m elevation and shown in Figure 2 agrees with these results, matching the VTEM response from mid-to late time with a 1/t 1.2 decay. For comparison, Figure 2 also shows the decay recorded at 120 m elevation, which appears unaffected by SPM and is matched by a 1/t 2.5 decay, as expected for dBz/dt data above a half-space (Spies and Frischknecht, 1991). Assuming a power-law decay 1/t k at late time, the power-law index k was derived from the data shown in Figure 1.…”

Section: Helicopter Take-off Datamentioning

confidence: 99%