Ionospheric influence on the seismo-telluric current related to electromagnetic signals observed before the Wenchuan <i>M</i><sub><i>S</i></sub> 8.0 earthquake
A three-layer (Earth–air–ionosphere) physical model, as well as a two-layer (Earth–air) model, is employed in this paper to investigate the ionospheric effect on the wave fields for a finite length dipole current source co-located at a hypocenter depth and along the main fault of an earthquake when...
| Main Authors: | , , |
|---|---|
| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2016-10-01
|
| Series: | Solid Earth |
| Online Access: | http://www.solid-earth.net/7/1405/2016/se-7-1405-2016.pdf |
| _version_ | 1819110777952403456 |
|---|---|
| author | M. Li H. Tan M. Cao |
| author_facet | M. Li H. Tan M. Cao |
| author_sort | M. Li |
| collection | DOAJ |
| description | A three-layer (Earth–air–ionosphere) physical model, as well as
a two-layer (Earth–air) model, is employed in this paper to investigate
the ionospheric effect on the wave fields for a finite length dipole current
source co-located at a hypocenter depth and along the main fault of an
earthquake when the distance between the epicenter and an observing station
is up to 1000 km or even more. The results show that all
electrical fields are free of ionospheric effects for different frequencies
in a relative short range, e.g., ∼ 300 km for <i>f</i> = 1 Hz,
implying the ionospheric influence on electromagnetic fields can be
neglected within this range, which becomes smaller as the frequency
increases. However, the ionosphere can give a constructive interference to
the waves passing through and make them decay slowly when an observation is
out of this range; moreover, the ionospheric effect can be up to 1–2 orders of magnitude of
the electrical fields. For a ground-based observable 1.3 mV m<sup>−1</sup> electric signal at <i>f</i> = 1 Hz 1440 km away from the Wenchuan
<i>M</i><sub><i>S</i></sub> 8.0 earthquake, the expected seismo-telluric current magnitude for
the Earth–air–ionosphere model is of 5.0 × 10<sup>7</sup><i>A</i>, 1
magnitude smaller than the current value of 3.7 × 10<sup>8</sup><i>A</i>
obtained by the Earth–air model free of ionospheric effects. This indicates
that the ionosphere facilitates the electromagnetic wave propagation, as if
the detectability of the system were improved effectively and it is easier
to record a signal even for stations located at distances beyond their
detectability thresholds. Furthermore, the radiating patterns of the
electrical field components |<i>E</i><sub><i>x</i></sub>| and |<i>E</i><sub><i>y</i></sub>| are
complementary to each other, although any two-dimensional (2-D) power distribution of
these components
shows strong power areas as well as weak ones, which is advantageous to
register a signal if the observing system is designed to measure both of
them instead of only one. |
| first_indexed | 2024-12-22T03:47:07Z |
| format | Article |
| id | doaj.art-f036232ceae246a29450370dc8b0b31a |
| institution | Directory Open Access Journal |
| issn | 1869-9510 1869-9529 |
| language | English |
| last_indexed | 2024-12-22T03:47:07Z |
| publishDate | 2016-10-01 |
| publisher | Copernicus Publications |
| record_format | Article |
| series | Solid Earth |
| spelling | doaj.art-f036232ceae246a29450370dc8b0b31a2022-12-21T18:40:07ZengCopernicus PublicationsSolid Earth1869-95101869-95292016-10-01751405141510.5194/se-7-1405-2016Ionospheric influence on the seismo-telluric current related to electromagnetic signals observed before the Wenchuan <i>M</i><sub><i>S</i></sub> 8.0 earthquakeM. Li0H. Tan1M. Cao2China Earthquake Networks Center, China Earthquake Administration, No. 5, Sanlihe Nanheng Street, Xicheng District, 100045 Beijing, ChinaChina University of Geosciences, No. 29, Xueyuan Road, Haidian District, 100083 Beijing, ChinaChina University of Geosciences, No. 29, Xueyuan Road, Haidian District, 100083 Beijing, ChinaA three-layer (Earth–air–ionosphere) physical model, as well as a two-layer (Earth–air) model, is employed in this paper to investigate the ionospheric effect on the wave fields for a finite length dipole current source co-located at a hypocenter depth and along the main fault of an earthquake when the distance between the epicenter and an observing station is up to 1000 km or even more. The results show that all electrical fields are free of ionospheric effects for different frequencies in a relative short range, e.g., ∼ 300 km for <i>f</i> = 1 Hz, implying the ionospheric influence on electromagnetic fields can be neglected within this range, which becomes smaller as the frequency increases. However, the ionosphere can give a constructive interference to the waves passing through and make them decay slowly when an observation is out of this range; moreover, the ionospheric effect can be up to 1–2 orders of magnitude of the electrical fields. For a ground-based observable 1.3 mV m<sup>−1</sup> electric signal at <i>f</i> = 1 Hz 1440 km away from the Wenchuan <i>M</i><sub><i>S</i></sub> 8.0 earthquake, the expected seismo-telluric current magnitude for the Earth–air–ionosphere model is of 5.0 × 10<sup>7</sup><i>A</i>, 1 magnitude smaller than the current value of 3.7 × 10<sup>8</sup><i>A</i> obtained by the Earth–air model free of ionospheric effects. This indicates that the ionosphere facilitates the electromagnetic wave propagation, as if the detectability of the system were improved effectively and it is easier to record a signal even for stations located at distances beyond their detectability thresholds. Furthermore, the radiating patterns of the electrical field components |<i>E</i><sub><i>x</i></sub>| and |<i>E</i><sub><i>y</i></sub>| are complementary to each other, although any two-dimensional (2-D) power distribution of these components shows strong power areas as well as weak ones, which is advantageous to register a signal if the observing system is designed to measure both of them instead of only one.http://www.solid-earth.net/7/1405/2016/se-7-1405-2016.pdf |
| spellingShingle | M. Li H. Tan M. Cao Ionospheric influence on the seismo-telluric current related to electromagnetic signals observed before the Wenchuan <i>M</i><sub><i>S</i></sub> 8.0 earthquake Solid Earth |
| title | Ionospheric influence on the seismo-telluric current related to
electromagnetic signals observed before the Wenchuan <i>M</i><sub><i>S</i></sub> 8.0 earthquake |
| title_full | Ionospheric influence on the seismo-telluric current related to
electromagnetic signals observed before the Wenchuan <i>M</i><sub><i>S</i></sub> 8.0 earthquake |
| title_fullStr | Ionospheric influence on the seismo-telluric current related to
electromagnetic signals observed before the Wenchuan <i>M</i><sub><i>S</i></sub> 8.0 earthquake |
| title_full_unstemmed | Ionospheric influence on the seismo-telluric current related to
electromagnetic signals observed before the Wenchuan <i>M</i><sub><i>S</i></sub> 8.0 earthquake |
| title_short | Ionospheric influence on the seismo-telluric current related to
electromagnetic signals observed before the Wenchuan <i>M</i><sub><i>S</i></sub> 8.0 earthquake |
| title_sort | ionospheric influence on the seismo telluric current related to electromagnetic signals observed before the wenchuan i m i sub i s i sub 8 0 earthquake |
| url | http://www.solid-earth.net/7/1405/2016/se-7-1405-2016.pdf |
| work_keys_str_mv | AT mli ionosphericinfluenceontheseismotelluriccurrentrelatedtoelectromagneticsignalsobservedbeforethewenchuanimisubisisub80earthquake AT htan ionosphericinfluenceontheseismotelluriccurrentrelatedtoelectromagneticsignalsobservedbeforethewenchuanimisubisisub80earthquake AT mcao ionosphericinfluenceontheseismotelluriccurrentrelatedtoelectromagneticsignalsobservedbeforethewenchuanimisubisisub80earthquake |