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Introduction to Earth System

Introduction to Earth System. Solid Earth part Rocco Malservisi roccom@lmu.de Phone: 2180 4201. Elastic Waves. P waves. Elastic Waves. S waves. Elastic Waves. Surface waves. Surface waves front expand as a cylindrical surface Body waves front expand as a spherical surface

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Introduction to Earth System

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  1. Introduction to Earth System Solid Earth part Rocco Malservisi roccom@lmu.de Phone: 2180 4201

  2. Elastic Waves P waves

  3. Elastic Waves S waves

  4. Elastic Waves Surface waves Surface waves front expand as a cylindrical surface Body waves front expand as a spherical surface Since the energy is conserved, which one is decaying faster? Body waves decay ~ as inverse of square of distance Surface waves decay ~ as inverse of the distance

  5. The same can be done with waves produced by earthquakes that Can travel through the planet

  6. PREM

  7. Tomography Flower, 2004 Data from Grand and Van Der Hilst

  8. Free oscillation Earth http://web.ics.purdue.edu/~nowack/geos557/lecture16-dir/lecture16.htm Toroidal Spheroidal

  9. 3D-MODELLE DES ERDMANTELS Kugelfunktionen Die Eigenschwingungsmoden der Erde lassen sich mit Hilfe von Kugelfunktionen beschreiben. Cnm sind die Kugelkoeffizienten vom Grad n und Ordnung m Zonale Komponente Cnm: n = 2, m = 0 Sektoral Komponente Cnm: n = 2, m = 2 Terrassal Komponente Cnm: n = 2, m = 0

  10. 3D-MODELLE DES ERDMANTELS Daten – III. Splitting der Eigenfrequenzen des Erdkörpers Berechnet man die Fourier-Transformation sehr langer Seismogramme (24 Stunden und länger) so tauchen die Eigenfrequenzen der Erde als klare Peaks im Spektrum auf. Amplitudenspektrum, Irian-Java-Beben, 17. 2. 1996, Station PTGA, Brasilien

  11. http://earthguide.ucsd.edu/mar/dec5/earth.html

  12. Magnetic Field

  13. We have a magnetic field that it is very similar to the one of a dipole. Well in reality this is true close to the surface if we go far away enough it looks more complex Magnetopause 10Re Moon 60Re

  14. Magnetic Field is a vector It has an intensity (can be measured looking At the oscillation of a compass) And a direction The direction change with the position Magnetic Pole: The place where the compass is pointing Down Magnetic Equator: The place where the compass is horizontal The Magnetic Poles are close to the geographical Poles but do not coincide (~11 off)

  15. The Earth’s Magnetic Field B = (X, Y, Z) Or B = (F, I, D ) OrB = (D, H, Z) F: intensity I: inclination D: declination H: Horizontal component The seven elements of the (local) magnetic fieldin the geographic coordinate system I. Geomagnetic field – Local Geomagnetic Field Vector

  16. The Earth’s Magnetic Field From this: Magnetic pole is the point where H=0 D= +- 90 Magnetic Equator the point where D=0 F: intensity I: inclination D: declination H: Horizontal component Where 3000nT<H<6000nT erratic zone (compass work badly) Where H<3000nT unusable zone (compass does not work) I. Geomagnetic field – Local Geomagnetic Field Vector

  17. Tesla (T) Magnetic flux density = Wb/m^2 Weber (Wb) The weber may be defined in terms of Faraday's law, which relates a changing magnetic flux through a loop to the electric field around the loop. A change in flux of one weber per second will induce an tension of one volt. T=N/Am V velocity m/s E electric field N/C V/m B=N/Am BiotSavart Law

  18. The place where the axis of the dipole intersect the surface Of the earth are called geomagnetic poles

  19. The numerical interpolation of the data is called Geomagnetic models. Every 5 yr a new model is released by The international community now we have the IGRF 2005 From Press, 1992. 90% of spatial field distribution can be explained by a simple dipolar field I. Geomagnetic field – Geocentric inclined dipole

  20. Magnetic Observatory http://www.ngdc.noaa.gov/seg/geomag/icons/Obs1999_lg.gif FUR http://www.geophysik.uni-muenchen.de/observatory/geomagnetism

  21. Geomagnetic models: Interpolation of the observations Using spherical harmonics. If we do not have electrical charges and magnetic sources We can have a potential. (otherwise it is not conservative so no potenzial) Gauss in 1830 thought that he can divide the field in internal And external having 2 potentials. The internal goes as r^-n the external as r^n The potential can be expressed as:

  22. This is not only an interpolation scheme but also the solution for the physical problem of the magnetic field due to an internal or external source! The coefficients are called Gauss coefficients The internal field coef. start from r^-2 because we do not have the magnetic monopole The internal field represent 90% of the total field

  23. Table 1. Spherical Harmonic Coefficient (in nT) of Terrestrial Magnetic Field (IGRF 1985) Coefficient Degree (m) Order (n) 1 2 3 4 ______________________________________________________ 4 169 gnm 3 835 -426 2 1691 1244 363 ______________________________________________________ 1 -1903 2045 -2208 780 gno 0 -29877 -2073 1300 937 1 5497 -2191 -312 233 ______________________________________________________ 2 -309 284 -250 hnm 3 -296 68 4 -298

  24. The internal field represent 90% of the total field The coef. g with n=1 m=0 give the magnitude of the dipole aligned with the rotation axis. The coef. with n=1 give the magnitude of the dipole is the largest one ~85% of the field. It is inclinated of ~11 degrees. For n>12 the coef. are neglegible. N=2 quadrupole etc… can be controlled by regional features.

  25. The numerical interpolation of the data is called Geomagnetic models. Every 5 yr a new model is released by The international community now we have the IGRF 2005 From Press, 1992. 90% of spatial field distribution can be explained by a simple dipolar field I. Geomagnetic field – Geocentric inclined dipole

  26. Geomagnetic Field Intensity Other units: Gauss=100000nT g=10000nT I. Geomagnetic field – Worldwide Variation of F

  27. Geomagnetic inclination (IGRF) I. Geomagnetic field – Worldwide Variation of I

  28. Worldwide Distribution of Geomagnetic Declination according to IGRF 2000 I. Geomagnetic field – Worldwide Variation of D

  29. The dipolar field is called the MAIN FIELD It changing slowly (this is why we update the model Every 5 yr by IAGA) The external field can change quickly. How does the field change: http://www.geophysik.uni-muenchen.de/observatory/geomagnetism Big diurnal variation and annual variation what can cause it?

  30. Temporal (diurnal and secular) variations 10 nT / hour other secular variation: reversal From Butler, Palaeomagnetism, 1992. Magnetic storm Slide I. Geomagnetic field – Temporal Variations Compare:X = 3 nT/km * 33 km/h => 100 nT/hY = 0.3 nT/km * 33 km/h => 10 nT/h,Thus, diurnal changes matter !

  31. other secular variation: reversal From Butler, Palaeomagnetism, 1992. Slide I. Geomagnetic field – Temporal Variations

  32. Where the magnetic field came from? Dipole inside the Earth can not have reversal b-c) Uniformly magnetic mantle Or core, mantle of silicate too hot d) Current in the core Most likely

  33. Where the magnetic field came from? Self Sustaining dynamo

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