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SUSHI II

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SUSHI II

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  1. SUSHI II Long-term stress modelling: Implications for large earthquake forecasting Suleyman S. Nalbant, John McCloskey, Shane Murphy, NunoSimao and Tony Lindsay Environmental Sciences Research Institute University of Ulster, Coleraine, Co. Derry, N. Ireland

  2. Background • There were two gigantic earthquakes on the Sunda megathrust in 2004 and 2005 with 3 months separation. • Stress transfer from these earthquakes sparkled a worry that Mentawai section would rupture soon

  3. Background • There were historical evidences that supported this worry. • A potential earthquake on the Mentawai section with a magnitude in the range of M~8.7-8.9 would have disastrous consequences. • A tsunami as a result of this potential earthquake would invade population centres along the west coast of Sumatra, specifically the city of Padang with 800,000 population.

  4. Padang Knowing slip distribution is important McCloskey et al EPSL 2008

  5. Motivation • Can we forecast a future earthquake with its possible rupture area and slip distribution on the Sunda megathrust? • To have a reliable answer to this question • stress/strain accumulation over at least a seismic cycle should be known; • Initial stress level before the last seismic cycle • Stress perturbation due to the all earthquakes in the last seismic cycle • Stress accumulation over inter-seismic periods.

  6. Strain accumulation • It is defined as the ratio of interseismic slip rate to plate convergence rate • Interseismic slip rates are inverted from geodetic and palaeogeodetic measurements. • strong coupling is a necessary • but not sufficient condition for high slip in a single event Chlieh et al. (2008) JGR Natawidjaja et al. (2006) JGR

  7. Rupture planes of all earthquakes M>7.0 occurred between 1797 and 2005 • (22 earthquakes)

  8. Slip Function for earlier historical earthquakes • Seismic moment is kept the same

  9. 1797-1833 • We are calculating stress changes assuming a ‘zero’ stress level in 1797.

  10. 1797-1861

  11. 1797-1931

  12. 1797-2004

  13. 1797-2005 The rupture limits may have been defined by the pre‐existing stress state shaped by previous earthquakes

  14. Rupture extend and slip distribution of the 1797 EQ Natawidjaja et al. 2006 (JGR)

  15. Rupture extend and slip distribution of the 1833 EQ • One thing we know for sure that slip distributions and rupture extend weren’t like this. Natawidjaja et al. 2006 (JGR)

  16. What do we know? Increasing Information Newcomb and McCann JGR 1987

  17. Class 4 February 16 1861 Eq Using Monte-Carlo method, we can produce many scenario earthquakes satisfying the observations

  18. Class 3 December 28 1935 Eq Location (lat/long) -0.06/98.21 Magnitude: 7.7

  19. Class 2 1797 and 1833 Eqs. Sumatra

  20. 1797 Fault Coupling 1833

  21. All events Year Month Day Long Lat Depth Mag. #Scenario Eq 1681 12 11 0 0 0 0 50 1756 11 3 0 0 0 0 50 1770 1 1 0 0 0 0 50 1797 2 10 0 0 0 8.6 10 1818 3 18 0 0 0 0 50 1818 5 1 0 0 0 0 50 1833 11 24 0 0 0 8.9 8 1843 1 5 0 0 0 0 50 1852 11 11 0 0 0 0 50 1861 2 16 0 0 0 8.5 50 1909 6 3 -2.00 101.00 0 7.7 50 1935 12 28 -0.06 98.21 0 7.7 50 1943 6 8 -2.82 102.09 0 7.3 50 1943 6 9 -0.94 100.91 0 7.6 50 1946 5 8 -0.51 99.31 0 7.1 50 1976 6 20 3.40 96.33 33 7.0 50 1984 11 17 0.20 98.30 33 7.2 50 2002 11 2 95.99 2.65 23 7.2 50 2004 12 26 94.26 3.09 29 9.0 1 2005 3 28 97.07 1.67 26 8.6 1 2007 9 12 100.99 -3.78 24 8.5 1 2007 9 13 99.39 -2.31 17 7.0 1 2008 2 20 95.98 2.69 15 7.3 1 2008 2 25 99.95 -2.66 14 7.2 1 2010 4 6 96.74 2.07 18 7.8 1 2010 5 9 95.78 3.36 37 7.2 1 2010 10 25 99.32 -3.71 12 7.8 1 Class 1 Modern Eqs

  22. Slip deficit scenarios; Which History is most likely?

  23. A preliminary result • The well-resolved red bulge under Siberut would produce an M8.7 earthquake if it all failed simultaneously.

  24. What’s next? Genetic algorithm for improved inversion for corals Searching for further coral displacements to constrain other historical earthquakes – particularly 1861 and 1935 Use Bayesian techniques to assess the probability of each model given the data and uncertainty Look at the stress field before recent damaging earthquakes Communicate risk mitigation by engaging key stakeholders, so that science-based hazard maps can be presented in a readily-understood local context

  25. 1797-2010

  26. 1797-2011

  27. From Loading and Earthquakes to Absolute Stress? Initial Slip Deficit Slip Deficit Interseismic Loading Seismic Slip - = + Interseismic Loading Plate Velocity Coupling =  Seismic Slip Sum of Slip distributions =

  28. 1797-2005