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The gravity effect of the subducted slab beneath the Vrancea Region, Romania

The gravity effect of the subducted slab beneath the Vrancea Region, Romania. Ron Hackney Institut für Geologische Wissenschaften Freie Universität Berlin Michael Martin, Alik Ismail-Zadeh Blanka Sperner, Dumitru Ioane CALIXTO Working Group. Aims.

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The gravity effect of the subducted slab beneath the Vrancea Region, Romania

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  1. The gravity effect of the subducted slab beneath the Vrancea Region, Romania Ron Hackney Institut für Geologische Wissenschaften Freie Universität Berlin Michael Martin, Alik Ismail-Zadeh Blanka Sperner, Dumitru Ioane CALIXTO Working Group

  2. Aims • To model the subducting slab beneath the Vrancea region • Is the slab associated with a significant gravity anomaly? • What gravimetric influence does the slab have?

  3. Acknowledgments Collaborative Research Centre 461 “Strong Earthquakes” Universität Karlsruhe Gravity Research Group Freie Universität Berlin

  4. Bouguer anomalies from Ioane (1994)

  5. EGM96Geoid expanded to degree and order 360

  6. The Vrancea Region • South-east Carpathians • Deep and large earthquakes • confined to surface area 30 by 80 km • depth range 70-180 km • define a near-vertical slab • Slab in the final stages of detachment after Miocene west-to-east slab roll-back (e.g. Sperner et al., 2001)

  7. Slab Evolution (B. Sperner, 2001)

  8. Seismicity Oncescu et al., (1999)

  9. Velocity to Density • Tomographic model developed at Universität Karlsruhe - SFB461 • Martin et al. (in press) • Convert velocities from tomography model to densities • pressure-dependant relationships of Krasovsky (1981, 1989)

  10. Modelling Procedure • Subtract background density  Dr • “Edge” of slab: Dr = 0.025 g/cm3 • Define a 3D slab body • series of east-west cross-sections • import to IGMAS modelling program • Determine gravity effect and compare to observed fields

  11. ModelLocation Dimensions 1000 x 1000 km

  12. Horizontal Slices N Dimensions: 1000 km x 1000 km

  13. VerticalSlices(east-west) Depth East-west distance Dimensions: 1000 km x 350 km

  14. “Slab” geometry ~100 km

  15. “Slab” geometry 350 km

  16. Still detaching Already detached 350 km Geometry is misleading!

  17. 0 Calculated Observed mGal -100 100 km 100 km Gravity Model west east

  18. 0 Calculated Observed mGal -100 100 km 100 km Gravity Model west east

  19. Results Observed Calculated

  20. Observed Residual

  21. Conclusions • Slab gravity effect is not obvious in observed data • Can’t constrain slab geometry from the gravity field • Slab gravity may be important when modelling foreland basin geometry

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