Simultaneous measurements of the total geomagnetic field intensity by the same type of the proton precession magnetometers at two stations in NW Turkey have been taken cooperatively by a research group since December 1970. Up to the end of July 1971 mainly three probable local magnetic changes were observed. It was seen that after a decrease in the local field at a magnetic station (Erdek) a few earthquakes occured at either nearly N or S of that station, and after an increase in the local field an earthquake took place nearly W of the same station. In this paper the data and some results of the first part of observations are given.
In Turkey, studies on the tectonomagnetic effect have started at the end of 1970. Taking simultaneous measurements of the total geomagnetic field at a few stations in NW Turkey by proton precession magnetometers, some tectonomagnetic effects up to 50 nT accompanying felt earthquakes are observed within the period December 1972-March 1975. A linear relation is obtained between the magnitude and distance of the earthquakes which are close to the magnetic stations (less than 75 km), and the observed tectonomagnetic effect.Temporary magnetic measurements along a profile show that the tectonomagnetic effect increases towards the fault.The last part of this study shows that it will be useful and possible to use the magnetic records of the Istanbul-Kandilli, Panagyurishte and Surlari observatories to compute tectonomagnetic effects of the past.
The sensitivity and the signal-to-noise ratio of an astatic magnetometer are proportional to the intensity of magnetization of each magnet in the suspended system. Hitherto the intensity of magnetization has been calculated using values of demagnetization factors for ellipsoids and have been applied to astatic design incorporating rectangular or cylindrical magnet forms.In the present paper, the magnetizations of both rectangular and cylindrical magnets have been calculated again using more exact values of the demagnetization factors for rectangular and cylindrical shapes, respectively. Then the calculated parameters for the astatic magnetometer in this study are compared with the previous calculations to show the effect of the demagnetization factors for ellipsoids on the theoretical calculations in the astatic design incorporating rectangular or cylindrical magnets. It is shown that the theoretical values of both sensitivity and signal-to-noise ratio of an astatic magnetometer are sensitivity (ellipsoid approx.)/sensitivity (exact shape) = 1.5; and signal-to-noise (ellipsoid approx.)/signal-to-noise (exact shape) = 2.0. These are lower than the values in previous calculation in the case of longitudinal magnets. But this previous assumption is not significant for transverse magnets, say FEROBA 111.
Some of these Cenozoic basalts are magnetized in either the normal or reversed direction of the axial dipole field but some others are magnetized obliquely. The remanences of the latter are quite as stable as the normal or reversed flows and are interpreted as recording geomagnetic field directions during polarity transitions. When combined with measurements made on rocks from sites some 10 km away from ours, two paths connecting these transitional virtual poles may be traced, one for the lower Pliocene and the other for the upper Pliocene. Both cross central Russia and the Indian Ocean. Palaeosecular variations of the geomagnetic field have been investigated by restricting our studies to flows which yield virtual poles at latitudes higher than 45" and the dispersion of cleaned R.M. directions obtained from such flows agree with world-wide average values. Thermomagnetic, ore microscope and electron microprobe investigations have been made and the shape of the thermomagnetic curves is related to evidence of both low and high temperature oxidation.
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