A new analysis and interpretation of geomagnetic variation anomalies in Southern California and in Peru
During the sixtieth of the last century networks of Askania variographs recorded in Southern California and in Peru geomagnetic time variations in the magnetic north (H), east (D) and vertical (Z) component to study local anomalies of their internal part by EM induction. A previous analysis of the Californian data has led to sets of GDS transfer functions for periods between 15 minutes and two hours, while for Peru so far only preliminary results have been reported. The still existing magnetograms of both surveys have been re-analysed and newly interpreted.The new analysis confirms the previously obtained results of the Californian data, but improves their accuracy.For Peru the new analysis formalizes the conclusions drawn formerly from visual inspections of magnetograms and peak-to-peak readings of selected events. Attempts have been made to extend the analysis to daily variations.In Peru a simplified line-current model yields the external part of the equatorial electro-jet at ground level. For the normal internal part of short-periodic day-time events a fitting layered deep structure is used, while assuming that the jet field of daily variations is without internal part.In order to substantiate necessary assumption about the deep structure offshore and onshore of Southern California, spatial gradient methods are applied to geomagnetic observatory data, including Fillouxs geomagnetic sea-bottom observations offshore Central California. For Horizontal Spatial Gradient Sounding the data base has been hourly mean values for six months at four geomagnetic observatories in the Western United States. For Vertical Gradient Sounding the Tucson observatory records in D are connected to those at the seabottom Assuming an exclusively local time dependence of daily variations, the Tucson data are projected to a point straight above the seafloor instrument. The similarity of results from both types of gradient soundings tentatively suggests a common 1D substructure offshore and onshore of Southern California. Also Rooneys eleven years of earth current observations in the vicinity of Tucson are re-examined with emphasis on daily variations.For interpretations the original 2D thin-sheet models are replaced by 3D thin-sheet models, using the integral equation method, but with Greens functions for the 1D substructure only. In this way it is possible to model the 2D ocean-continent transition with an imbedded central 3D region.
GDS anomalies equatorial electro-jet. thin-sheet models
Ulrich Schmucker
Planckstrasse 19 D-37073 Goettingen, Germany
国际会议
The 19th International Workshop on Electromagnetic Induction in the Earth(第十九届国际地球电磁感应学术研讨会)
北京
英文
885-888
2008-10-23（万方平台首次上网日期，不代表论文的发表时间）