22 - ERTH2&0&/1& Geomagnetic ha6ards 1...

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Unformatted text preview: ERTH2&0&/1& Geomagnetic ha6ards 1 GEOMAGNETIC HAZARDS Instructor: Claire Samson@ PhBDB@ PBEngB ERTH2&0&/1& Geomagnetic ha6ards 2 Lecture obFectives To describe the characteristics of the Earths magnetic field To describe solar activity To understand the interaction between the solar wind and the Earths magnetosphere@ and its conseNuences on technological systems ERTH2&0&/1& Geomagnetic ha6ards 3 Contents Electricity and magnetism The Earths magnetic field The internal geomagnetic field Solar activity and the external geomagnetic field Space weather ConseNuences on technological systems ERTH2&0&/1& Geomagnetic ha6ards & Electricity and magnetism ERTH2&0&/1& Geomagnetic ha6ards 5 Faradays law In the laboratory: Magnetic field variations induce an electrical current in a medium The induced current creates its own magnetic field ERTH2&0&/1& Geomagnetic ha6ards U N S A Magnetic field variations induce an electric current Author: SB HeffordB Shown with permissionB ERTH2&0&/1& Geomagnetic ha6ards W Faradays law In nature: Xariations in the Earths magnetic field induce electrical (Z telluric Z) currents In the ground \n electrically conducting networks Telegraph network Telephone lines and seafloor cables Pipelines Power transmission lines ERTH2&0&/1& Geomagnetic ha6ards ^ Magnetotelluric sounding Prospecting techniNue Record for a few hours to a few days Earths magnetic field Telluric currents Estimate the electrical conductivity in the subsurface Metallic ore bodies are more conductive than the surrounding rocks ERTH2&0&/1& Geomagnetic ha6ards _ Photo: IB Ferguson@ UB of Manitoba Magnetic sensors ERTH2&0&/1& Geomagnetic ha6ards 10 Photo: MB Folta@ Carleton UB Photo: Narod Geophysics. Shown with permission. ERTH2&0&/1& Geomagnetic ha6ards 11 Electrodes Photos: MB Folta@ Carleton UB ! 15 cm Photo: Phoenix GeophysicsB Shown with permissionB ERTH2&0&/1& Geomagnetic ha6ards 12 Photo: MB Folta@ Carleton UB ERTH2&0&/1& Geomagnetic ha6ards 13 Photo: CB Samson ERTH2&0&/1& Geomagnetic ha6ards 1& Electromagnetic surveying Prospecting techniNue GroundAbased or airborne Controlled experiment n artificial varying magnetic field induces currents in subsurface ore bodies These currents generate a magnetic field recorded at the surface Estimate the depth@ shape and electrical conductivity of subsurface ore bodies ERTH2&0&/1& Geomagnetic ha6ards 15 130m 50m 125m Transmitter Receiver Ore Body Subsurface X Y Z Secondary Field Primary Field Eddy Currents Author: SB HeffordB ShownwithpermissionB ERTH2&0&/1& Geomagnetic ha6ards 1U Photo: Fugro Airborne SurveysB Shown with permissionB ERTH2&0&/1& Geomagnetic ha6ards 1W ERTH2&0&/1& Geomagnetic ha6ards 1^ The Earths magnetic field (synB geomagnetic field ) ERTH2&0&/1& Geomagnetic ha6ards 1_ Geomagnetic ha6ards Extreme variations of the Earths magnetic field can have a significant effect on technological...
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This note was uploaded on 11/13/2011 for the course CIVE 2*** taught by Professor - during the Spring '11 term at Carleton CA.

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22 - ERTH2&0&/1& Geomagnetic ha6ards 1...

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