Geoelectromagnetic Earth Investigations

1. Geoelectromagnetic Earth Investigations By Adel Fathy M.Scstudet, Fayoum University Email: a_fathyallam@yahoo.com SWMC- Helwan University -23/11/2012

2. Outlines 1- Sun Earth connection. 1.1 Current system. 1.2 Geomagnetic indices. 1.3 Geo-Space connection. 2- Magnetotelluric. 2.1.Mechanism of magnetotelluric Method 2.2 Physics of Magnetotelluric Method. 2.2 Processing Method. 3- Geomagnetic Deep Sounding (GDS). 3.1 Physics of GDS. 4- Plane of the Work.

3. 1.1 Current System

4. 1.2 Geomagnetic indices • Three main indices for monitoring the strength of Earth’s magnetic field variations (Dst, AE, Kp) and others, Recently many indices are proposed for monitoring solar geomagnetic and Earth variations, such as; (Pc5 , EEJ, Pi 2 …etc). Menvielle and Marchaudon, 2008

5. The most intensive ground based magnetometer network distributed all over the world ITERMAGNET

6. 1.3 Geo-Space connection • Means here, using natural earth’s magnetic field for monitoring: 1- Seismic activity(Using Raw magnetic field and pulsations ). 2- Deep Earth’s layers conductivity. And interpreting some of the abnormal phenomena.

7. Conductivity Change ULF Emission ULF Emission Electromagnetic coupling of ULF waves in magnetospher-plasmasphere-ionosphere-lithosphere Yumoto et al., 2009

8. Abnormal field observations • Anomalous field enhanced due to 1- Seismic activity. 2- Costal effects. 3- A high conductive layer.

9. 2- Magnetotelluric (MT) • MTis an Electromagnetic method which uses natural electromagnetic fields (E and B) at the surface of the Earth to determine the distribution of electrical resistivity within the Earth and the deep structures. • This method is preferred due to, 1- Great depth of penetration over seismic 2- Provide information on non/poor seismic and good/poor conductors. • Recentlythe importance of MT and Audio MT methods are increased due to their use for the petroleum exploration. Electric field variations Magnetic field variations

10. 2.1.Mechanism of magnetotelluric Method • Naturally occurring variations (time varying) in the Earth’s magnetic fields induce electrical currents in conductive layers, which could be recorded at on the Earth’s surface . • Vertical wave attenuation characterized by a skin depth, which is proportional to the incidence wavelength. Ionospheric and Magnetospheric currents EARTH Bz Induced current due to Earth’s conductivity Conductive layer

11. 2.2 The Physics of MT Method Faraday’s and Ampere’s law for a time varying electric and magnetic fields are: 2.1 2.2 Curl of both equations are: 2.3 2.4 In source free medium, Div (E and H)=0 Be the propagation constant of the medium

12. Ignoring the displacement current, from Equation (1) we get, 2.5 2.6 2.7 2.8 The impedance within the medium is given by, 2.9

13. Generally sounding the deep Earth conductivity using long period waves. 1- long period pulsations Pc3. 2- Sq current . 3- Electrojet currents . 4- Dp1 currents. 5- Magnetovariations (long magnetic field variations due to magnetic storms) which is preferable. • Processing methods 1- Collecting noiseless data (Electric and magnetic or Magnetic only). 2- Spherical harmonic analysis. 3- Modeling the data to calculate the conductivity.

14. 3- Geomagnetic Deep Sounding (GDS) GDS depends on the relation between the variations in the geomagnetic field components induced by external currents of the geomagnetic field at the Earth’s surface, depend on the Earth conductivity

15. Conductor at some depth Secondary field at the earth’s surface will be weaker than the primary one and the vertical component will be greater

16. Physics of magneto variational profile (MVP) in SphericalHarmonic Analysis (SHA) • From Maxwell’s equations • Where Spherical coordinates (R,Ө,Ø) Harmonic Time varying field exp(iωt)

17. The magnetic ratio and the Earth impedance F is the radial part in the Spherical analysis Magnetic ratio (W)= Radial magnetic component / horizontal component Impedance = Electric field component / its corresponding magnetic component Generally, GDS can provide information on the Earth’s conductivity down to ~ 1800 km according to the field frequency used

18. Earth’s magnetic field on its surface 1- BoePrimarypart on external origin. 2- Boi, Secondary normal part due to induced currents in Earth’s layers. 3- Ba, Secondary anomalous part • Generally, Normal field Bo= Boe+Boi And the total field is denoted by • B= Bo+ Ba • Anomalous part formed in an elongated area in the X direction is known to be polarized with Expolarization (By,Bz,Ex). Observatory Z X Y

19. Outside the anomalous region the Cauchy formula for contour enclosing the upper half space with no field sources. From Kertz, (1954) to external and internal field could be separated U =U e +Ui

20. 3.1 Anomalous field determination using a reference point B(R1) magnetic field at the observation point, and B(R2) is the magnetic field at the reference station. [b(R1R2)] is the transformation matrix B(R2) B(R1) A high conductive body (layer)

21. 3.2 Profile (Array) data processing 1- Separation of the normal fields. 2- Anomalous field determination Ba. 3- solving Schmucker (1964, 1970) for bik tensor components. Bo= Boe+ Boi Ba P and q are the perturbation vectors which are used to show the strength and the direction of anomalous currents P, q and C (The induction vector) indicate clearly the structure of the anomalous field

22. 3.3 Processing of the point observation Both A and B characterizing the electrical conductivity Where H, D and Z are the field components composed of normal and anomalous parts Calculated as follow A and B can be found approximately due to their dependence on the normal field polarization

23. 4- Plane of the Work.

24. Thank you