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| Titel |
Estimating the seismotelluric current required for observable electromagnetic ground signals |
| VerfasserIn |
J. Bortnik, T. E. Bleier, C. Dunson, F. Freund |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
0992-7689
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| Digitales Dokument |
URL |
| Erschienen |
In: Annales Geophysicae ; 28, no. 8 ; Nr. 28, no. 8 (2010-08-31), S.1615-1624 |
| Datensatznummer |
250016875
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| Publikation (Nr.) |
 copernicus.org/angeo-28-1615-2010.pdf |
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| Zusammenfassung |
| We use a relatively simple model of an underground current source co-located
with the earthquake hypocenter to estimate the magnitude of the
seismotelluric current required to produce observable ground signatures. The
Alum Rock earthquake of 31 October 2007, is used as an archetype of a
typical California earthquake, and the effects of varying the ground
conductivity and length of the current element are examined. Results show
that for an observed 30 nT pulse at 1 Hz, the expected seismotelluric current
magnitudes fall in the range ~10–100 kA. By setting the detectability
threshold to 1 pT, we show that even when large values of ground conductivity
are assumed, magnetic signals are readily detectable within a range of 30 km
from the epicenter. When typical values of ground conductivity are assumed,
the minimum current required to produce an observable signal within a 30 km
range was found to be ~1 kA, which is a surprisingly low value.
Furthermore, we show that deep nulls in the signal power develop in the
non-cardinal directions relative to the orientation of the source current,
indicating that a magnetometer station located in those regions may not
observe a signal even though it is well within the detectable range. This
result underscores the importance of using a network of magnetometers when
searching for preseismic electromagnetic signals. |
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