American Geophysical Union Become an AGU Member
Subscribe to AGU Journals		 AGU Home AGU Publications

Read Full Article (file size: 1300506 bytes)    Cited by

JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 108, NO. B5, 2254, doi:10.1029/2002JB001786, 2003

Lower mantle conductivity anomalies estimated from geomagnetic jerks

Hiromichi Nagao

Department of Geophysics, Graduate School of Science, Kyoto University, Kyoto, Japan


Toshihiko Iyemori

Data Analysis Center for Geomagnetism and Space Magnetism, Graduate School of Science, Kyoto University, Kyoto, Japan


Tomoyuki Higuchi

Institute of Statistical Mathematics, Tokyo, Japan


Tohru Araki

Department of Geophysics, Graduate School of Science, Kyoto University, Kyoto, Japan


Abstract

The occurrence epochs and duration periods of the 1969, 1978, and 1991 geomagnetic jerks are estimated for 65 geomagnetic observatories by applying a statistical time series model to monthly means of the geomagnetic eastward component. It is found for every jerk that the occurrence epochs around South Africa and South Pacific Ocean are delayed several years from those in other regions. Moreover, it is found for the 1969 and 1978 jerks that the duration times around South Africa, which are defined as the lengths of the duration periods, are longer than those in other regions. The distribution of these anomalous regions of the jerks (i.e., South Africa and South Pacific Ocean) may imply the existence of higher conductivities in the lower mantle beneath these regions, which possibly relates to the fact that the velocity of a seismic S wave in the D″ layer beneath these regions is slower than that in other regions. The mantle conductivities beneath South Africa, South Pacific Ocean, and other regions are estimated through a numerical simulation; the magnetic diffusion equation in the mantle is solved for an abrupt magnetic change generated at the core-mantle boundary. Comparing the results obtained by the simulation with those obtained by the data analysis, it is plausible that the mantle conductivities beneath South Africa and South Pacific Ocean are higher than that beneath other regions, although there is an ambiguity in the estimated magnitudes of the mantle conductivity.

Published 16 May 2003.

Index Terms: 1510 Geomagnetism and Paleomagnetism: Dynamo theories; 1517 Geomagnetism and Paleomagnetism: Magnetic anomaly modeling; 1530 Geomagnetism and Paleomagnetism: Rapid time variations; 1545 Geomagnetism and Paleomagnetism: Spatial variations (all harmonics and anomalies); 1560 Geomagnetism and Paleomagnetism: Time variations—secular and long term.

Read Full Article (file size: 1300506 bytes)    Cited by

Citation: Nagao, H., T. Iyemori, T. Higuchi, and T. Araki (2003), Lower mantle conductivity anomalies estimated from geomagnetic jerks, J. Geophys. Res., 108(B5), 2254, doi:10.1029/2002JB001786.