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3 rd MagNetE Workshop on European Geomagnetic Repeat Station Survey

3 rd MagNetE Workshop on European Geomagnetic Repeat Station Survey. GEOMAGNETIC VARIATIONS AND EARTHQUAKE ACTIVITY. Gerald Duma Central Institute for Meteorology and Geodynamics Vienna, Austria. Observations (1996) – daily range. AUSTRIA M  2.5, 1901-1990. Geomagnetic Observatory.

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3 rd MagNetE Workshop on European Geomagnetic Repeat Station Survey

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  1. 3rd MagNetE Workshopon European Geomagnetic Repeat Station Survey GEOMAGNETIC VARIATIONS AND EARTHQUAKE ACTIVITY Gerald Duma Central Institute for Meteorology and Geodynamics Vienna, Austria

  2. Observations (1996) – daily range AUSTRIAM  2.5, 1901-1990 Geomagnetic Observatory

  3. Observations (1997) – daily range Mt. VESUVIUS volcanic eqs, area 10 x 10 km , 1.8  M3.1, 1972-1996, 1400 events Duma, Vilardo (INGV), 1998 Geomagnetic Observatory

  4. A seismic daily cycle • Greek philosophers • Pliny the Elder,  79 A.D. eruption of Mt.Vesuvius • Conrad, 1932 • Shimshoni, 1972 • Rarely investigated in recent decades

  5. A seismic daily cycle 3 sub-periods 20th century AUSTRIA M  2.5 May 31 – June 18, 1997 Earthquake swarm in Austria, region IMST

  6. A seismic daily cycle • Observed also in many other regions • Earthquakes M  5 and 6 • A very powerful geodynamic process acting!

  7. Observations (1996) – long term AUSTRIAM  3.1 (Io  5°) Obs WIK, comp N Geomagnetic Observatory

  8. Mechanism, models? • Dependence on Local Time  Process related to sun • A mechanism which penetrates the whole Earth‘s lithosphere • Tides ? -> No! • High energy mechanism • Can a few nT influence tectonic performance?

  9. The electromagnetic model • Geomagnetic variations reach deep into the Earth‘s interior, 100s and 1000s of km! (magnetotellurics) • Maxwell‘s equations : E - H relation () • Earth‘s conductive lithosphere: „telluric currents“ associated with all geomagnetic variations • Applies to all natural variations in a broad frequency range (from Hz – solar cycle)

  10. The electromagnetic model • Telluric currents and forces F = e . [ ve . B ] F ... mechanic force vector e ... electron charge ve ... velocity vector B ... magnetic field vector ‚Lorentz force‘ ve e B F

  11. The electromagnetic model • Magnetic observatories monitor vertical force Fv (t)

  12. The electromagnetic model • Regional mechanic moment, torque Tr P1 P2 r I2 ≠ I1

  13. A new meaning of variation H H: monitors change (t) of vertical force Fv in P gradient H: monitors change (t) of regional mechanic moment Tr ( azimuth Az) P Torque axis

  14. Energy – diurnal variation • Sq: solar controlled, heating, ionization, tides(Chapman, Bartels, 1940)

  15. Energy – diurnal variation • The dayside Sq lithospheric current vortex (Matsushita, 1968) A large scale current field, covering  1/3 of the northern Earth‘s hemisphere T = MM x H

  16. Energy – diurnal variation • The mechanic moment of Sq for a single loop (Duma, Ruzhin, 2003) The example demonstrates: The deformation energy provided to the lithosphere by a single current loop, radius 1500 km and current 10 kA, is equivalent to the energy of an earthquake M 5,1.

  17. Energy – diurnal variation • 60% of total moment concentrates in a 30° segment H I

  18. Modelling the electromagnetic effect • Data for H(lat,long) to compute gradient • Hourly values (diurnal variation): • Model simulating Sq telluric current vortex • Regional observatory data (average Sq-var.) • Annual values (long term, secular variation): • Retrieved from IGRF, 1900-2010 (grid data) • Regional observatory data (annual means, SV)

  19. Case studies – Regions Austria Taiwan California Baikal region

  20. Case studies – Austria(M ≥ 3.2, Gradient H – N10W) Diurnal range Long term Gradient H from IGRF10 (1900-2010) Gradient H from Sq-Model 1900 - 2003

  21. Case studies – Taiwan(M ≥ 5, Gradient H – N55E) Diurnal range Long term Gradient H from IGRF10 (1900-2010) Gradient H from Sq-Model 1973 - 1998

  22. Case studies – Baikal area(M ≥ 5, Gradient H – N00E) Diurnal range Long term Gradient H from Sq-Model Gradient H from IGRF10 (1900-2010) 1900 - 1980 2001 - 2006

  23. Case studies – California(M ≥ 6, Gradient H – N30E) Diurnal range Long term Gradient H from IGRF10 (1900-2010) Gradient H from Sq-Model 1970 - 2005

  24. Novel aspects • Geomagnetic variations modulate (trigger) seismic activity • Answer to daily rhythm of seismic activity • Activity ‚controlled‘ by external sources (sun, magnetic dynamo) • Monitoring: directly by geomagnetic observatories • Predictability: systematic diurnal, seasonal, secular variations (IGRF 2010) • Not yet investigated: influence of magnetic storms

  25. Thank your for your attention !

  26. A surprising but plausible model Magnetic observatories monitor horizontal force FhC (t)

  27. Mt. VESUVIUS – long termvolcanic eqs, area 10 x 10 km , 1.8  M3.1, 1972-1996, 1400 events Observations – sun spot cycles Duma, Vilardo (INGV), 1998 Duma, Vilardo (INGV), 1998 n: annual number of eqs M  1.8, 1972-1996 sf: annual number of solar flares (103)

  28. Observations – daily range ITALY, 4 subregions / IONIAN ILANDS (G4)1910 – 1980, M  5 I1 I4 all Italy I2 I3 G4

  29. The regional torque Tr – Energy> lithosphere block model <

  30. Model of Sq telluric current vortex • Fits observed Sq-variations at observatories • Computes grad H(LT)

  31. H – current density

  32. Case studies – Austria(M ≥ 2.5, gradient H – N10W) Seasonal range, 2001 - 2005 H data from observatories - monthly mean values

  33. Case studies – Austria(M ≥ 2.5, gradient H – N10W) Seasonal range, 2001 - 2005 Gradient H from observatories - monthly mean values 2001 2003 2002 2004

  34. Case studies – Austria(M ≥ 2.5, gradient H – N10W) Seasonal range, 2001 - 2005 Gradient H from observatories - monthly mean values 2005

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