Electroseismic Waves From Point Sources In Layered Media
The macroscopic governing equations controlling the coupled electromagnetics and acoustics of porous media are numerically solved for the case of a layered poro-elastic medium.It is shown that these coupled equations decouple into two equation sets describing two uncoupled wavefield pictures. That i...
| Main Authors: | , |
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| Other Authors: | |
| Format: | Technical Report |
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Massachusetts Institute of Technology. Earth Resources Laboratory
2012
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| Online Access: | http://hdl.handle.net/1721.1/75261 |
| _version_ | 1811093012282867712 |
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| author | Haartsen, Matthijs W. Toksoz, M. N. |
| author2 | Massachusetts Institute of Technology. Earth Resources Laboratory |
| author_facet | Massachusetts Institute of Technology. Earth Resources Laboratory Haartsen, Matthijs W. Toksoz, M. N. |
| author_sort | Haartsen, Matthijs W. |
| collection | MIT |
| description | The macroscopic governing equations controlling the coupled electromagnetics and acoustics of porous media are numerically solved for the case of a layered poro-elastic medium.It is shown that these coupled equations decouple into two equation sets describing two uncoupled wavefield pictures. That is, the PSVTM picture where the compressional and vertical polarized mechanical waves drive currents in the PSV particle motion plane that couples to the electromagnetic wavefield components of the TM mode. And the SHTE picture where the horizontal polarized rotational mechanical waves drive currents in the SH particle motion plane that couples to the electromagnetic wavefield
components of the T E mode. The global matrix method is employed in computing
electroseismograms in layered poro-elastic media in the PSVTM picture.
The principal features of the converted electromagnetic signals are the following:
(1) contacts all antennas at approximately the same time; (2) arrives at the antennas
at half of the seismic traveltime at normal incidence reflected P waves; and (3) changes
sign on opposite sides of the shot.
The seismic pulse is shown to induce electric fields that travel with the compressional
wavespeed and magnetic fields that travel with the rotational wavefield. The frequency
content of the converted electromagnetic field has the same frequency content of the
driving incident seismic pulse, as long as the propagation distances are much less than
the electromagnetic skin depth.
Snapshots in time and converted electromagnetic amplitudes versus seismic point
source-antenna offset-are calculated for contrasts in mechanical and/or electrical medium
property. Conversion happens there where the seismic wavefront passes a contrast in
medium properties due to generated imbalances in current across the contrast. The TM
component amplitude radiation pattern away from the interface shows similarities with an effective electric dipole radiation pattern, or its dual, an effective magnetic current
loop radiation pattern centered right beneath the source at the contrast's depth. The
TM mode amplitudes decay rapidly with traveled distance and suggest the importance
of a Vertical Electroseismic Profiling geometry to enhance recording of the converted
electromagnetic signal by positioning the antennas closer to the target (contrast) of
interest. |
| first_indexed | 2024-09-23T15:38:10Z |
| format | Technical Report |
| id | mit-1721.1/75261 |
| institution | Massachusetts Institute of Technology |
| last_indexed | 2024-09-23T15:38:10Z |
| publishDate | 2012 |
| publisher | Massachusetts Institute of Technology. Earth Resources Laboratory |
| record_format | dspace |
| spelling | mit-1721.1/752612019-04-10T18:05:19Z Electroseismic Waves From Point Sources In Layered Media Haartsen, Matthijs W. Toksoz, M. N. Massachusetts Institute of Technology. Earth Resources Laboratory Haartsen, Matthijs W. Toksoz, M. N. The macroscopic governing equations controlling the coupled electromagnetics and acoustics of porous media are numerically solved for the case of a layered poro-elastic medium.It is shown that these coupled equations decouple into two equation sets describing two uncoupled wavefield pictures. That is, the PSVTM picture where the compressional and vertical polarized mechanical waves drive currents in the PSV particle motion plane that couples to the electromagnetic wavefield components of the TM mode. And the SHTE picture where the horizontal polarized rotational mechanical waves drive currents in the SH particle motion plane that couples to the electromagnetic wavefield components of the T E mode. The global matrix method is employed in computing electroseismograms in layered poro-elastic media in the PSVTM picture. The principal features of the converted electromagnetic signals are the following: (1) contacts all antennas at approximately the same time; (2) arrives at the antennas at half of the seismic traveltime at normal incidence reflected P waves; and (3) changes sign on opposite sides of the shot. The seismic pulse is shown to induce electric fields that travel with the compressional wavespeed and magnetic fields that travel with the rotational wavefield. The frequency content of the converted electromagnetic field has the same frequency content of the driving incident seismic pulse, as long as the propagation distances are much less than the electromagnetic skin depth. Snapshots in time and converted electromagnetic amplitudes versus seismic point source-antenna offset-are calculated for contrasts in mechanical and/or electrical medium property. Conversion happens there where the seismic wavefront passes a contrast in medium properties due to generated imbalances in current across the contrast. The TM component amplitude radiation pattern away from the interface shows similarities with an effective electric dipole radiation pattern, or its dual, an effective magnetic current loop radiation pattern centered right beneath the source at the contrast's depth. The TM mode amplitudes decay rapidly with traveled distance and suggest the importance of a Vertical Electroseismic Profiling geometry to enhance recording of the converted electromagnetic signal by positioning the antennas closer to the target (contrast) of interest. United States. Dept. of Energy. Office of Energy Research (Grant DE-FG02-93ERI4322) 2012-12-05T20:58:43Z 2012-12-05T20:58:43Z 1995 Technical Report http://hdl.handle.net/1721.1/75261 Earth Resources Laboratory Industry Consortia Annual Report;1995-13 application/pdf Massachusetts Institute of Technology. Earth Resources Laboratory |
| spellingShingle | Haartsen, Matthijs W. Toksoz, M. N. Electroseismic Waves From Point Sources In Layered Media |
| title | Electroseismic Waves From Point Sources In Layered Media |
| title_full | Electroseismic Waves From Point Sources In Layered Media |
| title_fullStr | Electroseismic Waves From Point Sources In Layered Media |
| title_full_unstemmed | Electroseismic Waves From Point Sources In Layered Media |
| title_short | Electroseismic Waves From Point Sources In Layered Media |
| title_sort | electroseismic waves from point sources in layered media |
| url | http://hdl.handle.net/1721.1/75261 |
| work_keys_str_mv | AT haartsenmatthijsw electroseismicwavesfrompointsourcesinlayeredmedia AT toksozmn electroseismicwavesfrompointsourcesinlayeredmedia |