|
Titel |
Influence of seismic activity in the atmospheric electrical field in Lisbon (Portugal) from 1961 until 1991 |
VerfasserIn |
Hugo Gonçalves da Silva, Cláudia Serrano, António Domingos Heitor Silva Reis, Mourad Bezzeghoud, Rui Namorado Rosa, José Fernando Borges, Bento Caldeira, Mouhaydine Tlemçani, Pier Francesco Biagi |
Konferenz |
EGU General Assembly 2011
|
Medientyp |
Artikel
|
Sprache |
Englisch
|
Digitales Dokument |
PDF |
Erschienen |
In: GRA - Volume 13 (2011) |
Datensatznummer |
250052221
|
|
|
|
Zusammenfassung |
The atmospheric electric field (AEF) can be influenced by different factors like cosmic
radiation, radioactivity and aerosols [1]. Two innovative works have shown the possibility of
enhanced air ionization, with consequent AEF perturbations, in the preparatory stage of
earthquakes (EQ): Freund et al. [2] base their arguments on charge separation generated
in the stressed volume followed by positive charges flow that reach surface and
ionize the air within the boundary layer; Harrison et al. [3] relate possible AEF
anomalies during the EQ preparation with surface air ionization through radon
emanations.
It is clear that AEF plays a role in many of the studied electromagnetic seismic
precursors, but systematic pre-earthquake AEF measurements are still lacking. There are
reports of AEF anomalies [4], but no clear conclusions could yet be drawn. Hence we believe
that in near future a deeper inspection of AEF is required since it could be vital for a better
comprehension of these phenomena.
Here we consider hourly values of the AEF recorded at Portela-Lisbon meteorological
station (38º47’N, 9º08’W) in the period 1961–1991. They were recorded with a Benndorff
electrograph at 1m-height probe. The data series was interrupted in 1975–1977 when the
electrometer was switched off for maintenance. The continuous and reliable data of AEF
observed are used to study the correlation between possible anomalies in AEF and
occurrence of eleven EQ with magnitude (M) above three. These verify the condition
that the distance between the AFE sensor to the EQ epicentre lies inside the EQ
preparation radius, R = 100.43M [5]. The influences of meteorological variables
(relative humidity, precipitation, wind intensity and cloudiness) are considered
too.
We also analyze the atmospheric radon concentration in the same period since radon is
important to estimate the alteration of the AEF conditions in response to the crustal
behaviour. In fact, EQ’s originate many factures in the Earth surface that create
many pathways for radon in the crust thus enhancing its migration [6], which may
lead to the enormous release into the atmosphere and consequently decrease in the
AEF.
We are just starting a very careful study and for the moment we do not have clear proves
to confirm or denied an EQ-AEF correlation. Nevertheless, it is important to mention that a
previous case study has given interesting results [7].
[1] Serrano, C., Reis, A.H., Rosa, R., and Lucio, P.S.: Influences of cosmic
radiation, artificial radioactivity and aerosol concentration upon the fair-weather
atmospheric electric field in Lisbon (1955–1991), Atmospheric Research 81, 236,
2006.
[2] Freund, F.T., Kulahci, I.G., Cyr, G., Ling, J., Winnick, M., Tregloan-Reed, J., Freund,
M.M.: Air ionization at rock surfaces and pre-earthquake signals, Journal of Atmospheric and
Solar-Terrestrial Physics 71, 1824, 2009.
[3] Harrison, R.G., Aplin, K.L., and Rycroft, M.J.: Atmospheric electricity coupling
between earthquake regions and the ionosphere, Journal of Atmospheric and Solar-Terrestrial
Physics 72, 376, 2010.
[4] Kachakhidze, N. Kachakhidze, M., Kereselidze, Z., and Ramishvili, G.: Specific
variations of the atmospheric electric field potential gradient as a possible precursor of
Caucasus earthquakes, Nat. Hazards Earth Syst. Sci., 9, 1221, 2009.
[5] Dobrovolsky,I.P., Zubkov,S.I., and Miachkin,V.I.: Estimation of the size of earthquake
preparation zones, Pure Appl. Geophys. 117, 1025, 1979.
[6] Kawada, Y., Nagahama, H., Omori, Y., Yasuoka, Y., Ishikawa, T., Tokonami, S.,
Shinogi, M.: Time-scale invariant changes in atmospheric radon concentration and
crustal strain prior to a large earthquake. Nonlin. Processes. Geophys. 14, 123,
2007.
[7] Silva, H.G., Bezzeghoud, M., Reis, A.H., Rosa, R.N., Tlemçani, M., Araújo, A.A.,
Serrano, C., Borges, J.F., Caldeira, B. and Biagi, P.F.: Atmospheric electrical field anomalies
associated with seismic activity (submitted to NHESS). |
|
|
|
|
|