HR: 0800h
AN: GP11A-0816    [Abstracts]
TI: Three-dimensional Electromagnetic Modeling of the Hawaiian Swell
AU: * Avdeev, D
EM: davdeev@cp.dias.ie
AF: Geoelectromagnetic Research Institute, Russian Academy of Sciences, 142190 Troitsk, Moscow Region, Russia, Troitsk, 142190 Russian Federation
AU: * Avdeev, D
EM: davdeev@cp.dias.ie
AF: present address: Dublin Institute for Advanced Studies, 5 Merrion Square, Dublin 2, Ireland, Dublin, Dublin 2 Ireland
AU: Utada, H
EM: utada@eri.u-tokyo.ac.jp
AF: Earthquake Research Institute, University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-0032, Japan, Tokyo, 113-0032 Japan
AU: Kuvshinov, A
EM: alexei@dsri.dk
AF: Geoelectromagnetic Research Institute, Russian Academy of Sciences, 142190 Troitsk, Moscow Region, Russia, Troitsk, 142190 Russian Federation
AU: Kuvshinov, A
EM: alexei@dsri.dk
AF: Earthquake Research Institute, Danish Space Research Institute, DK-2100, Copenhagen, Denmark, Copenhagen, DK-2100 Denmark
AU: Koyama, T
EM: tkoyama@jamstec.go.jp
AF: Japan Agency for Marine-Earth Science and Technology, Natsushima, 2-15, Yokosuka, 237-0061, Japan, Yokosuka, 237-0061 Japan
AB: An anomalous behavior of the geomagnetic deep sounding (GDS) responses at the Honolulu geomagnetic observatory has been reported by many researchers. Kuvshinov et al (2004) found that the predicted GDS Dst C-response does not match the experimental data -- 10-20% disagreement occurs for all periods of 2 to 30 days, qualitatively implying a more resistive, rather than conductive, structure beneath the Hawaiian Islands. Simpson et al. (2000) found that the GDS Sq C-response at the Honolulu observatory is about 4 times larger than that at a Hawaii island site, again suggesting a more resistive (than elsewhere around) structure beneath the observatory. Constable and Heinson (2004, http://mahi.ucsd.edu/Steve/swell.pdf), presenting a 2-D interpretation of the magnetotelluric (MT) and GDS responses recently obtained at 7 seafloor sites to the south of the Hawaii Islands, concluded that the dataset require the presence of a narrow conducting plume just beneath the islands. The main motivation of our work is to reveal the reason of the anomalous behavior of the Honolulu response. Obviously, the cause may be due to heterogeneity of either the conductivity or the source field. We examine this problem in some detail with reference to the Constable and Heinson's seafloor dataset, as well as the available dataset from the Honolulu observatory. To address the problem we apply numerical modeling using the three-dimensional (3-D) forward modeling code of Avdeev et al. (1997, 2002). With this code we simulate various regional 3-D conductivity models that may produce EM responses that better fit the experimental datasets, at least qualitatively. Also, to explain some features of the experimental long-period GDS responses we numerically studied a possible effect in the responses caused by the equatorial electrojet. Our 3-D modeling results show that, in particular: (1) The GDS responses are better explained by models with a resistive lithosphere whereas the MT data are better fit by models without one; (2) A conductive plume under the Hawaiian Islands may not be required by the MT and GDS datasets considered; (3) An equatorial electrojet might affect the imaginary part of the GDS responses at periods of 2 h and more; (4) The anomalous large value of 0.4 observed in the real part of the seafloor GDS responses still cannot be explained by the 3-D models considered. It seems to require more complicated models.
DE: 3210 Modeling
DE: 3230 Numerical solutions
DE: 1515 Geomagnetic induction
DE: 0644 Numerical methods
DE: 0925 Magnetic and electrical methods
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2004 AGU Fall Meeting