Real-time application of Coulomb stress modelling and related issues

1. Real-time application of Coulomb stress modelling and related issues By Suleyman S. Nalbant, Sandy Steacy & John McCloskey Geophysics Research Group, University of Ulster, N. Ireland

2. Motivation • There is a growing demand from the public, governmental natural hazard managing agencies and civil protection groups for having an updated seismic hazard assessment following a major earthquake in real or near real-time.

3. Scientific Questions • Is Coulomb stress technique (CST) a feasible method for seismic hazard update? • Can it be applied in near real-time? • What are the requirements for applying CST? • What would be the protocols for passing the results to end-users and informing the public?

4. Is it a feasible method? • ‘The 17 August 1999 earthquake increased the earthquake risk on the Yalova segment, that is, the western continuation of the northern strand toward the Marmara Sea, and the Düzce-Bolu segment at the eastern part of the Düzce-Hendek fault.’ Published 17 September 1999 From Barka, 1999, Science

5. Is it a feasible method? From Parsons et al., 2000, Science

6. Chen Ji, 2005 http://neic.usgs.gov

7. Is it a feasible method? • ‘The results indicate that although a subduction-zone event in the Sunda trench has been made more likely by the Sumatra–Andaman earthquake, at present the increase in stress is localized on the north of this segment. The effect might be expected to spread further south in the months ahead as a result of viscoelastic relaxation in the lower crust,… ’ Published 17 March 2005 From McCloskey et al. , 2005 Nature

8. Is it a feasible method?

9. Can it be applied in near real-time? • Both the 1999 Izmit –Duzce couple and 2004 –2005 Sumatran earthquakes occurred almost 3 months apart • This means researchers had time to do their calculation and seismic hazard updating before the subsequent event occurred.

10. What are the requirements for applying CST? True location of the source earthquake and rupture geometry • Slip distribution • A well-trained team

11. A well-trained team • Has to know assumptions behind the stress calculations techniques • 2-D optimally oriented planes • 3-D optimally oriented planes • On the structure • On main structural trend • Able to extract necessary info through the internet • Able to understand seismotectonic structure of the region in question • Have the knowledge of historical time seismic activity

12. From slip distribution • Compute stress tensor • Resolve into Coulomb stress Coulomb stress formulation

13. Coulomb stress Calculations, Calculating s. on 2-D oop • The orientation of the oop are strongly depend on the orientation of the regional stress field From King et al. , 1994, BSSA

14. Coulomb stress Calculations, Calculating s. on 3-D oop • 2-D • 3-D • Regional stress From McCloskey et al., 2003, GRL

15. Coulomb stress Calculations, Calculating s. on the mean structure From McCloskey et al., 2003, GRL

16. Coulomb stress Calculations, Calculating s. on the structure From McCloskey et al., 2005, Nature

17. True location of the source earthquake and rupture geometry • An earthquake in S. California • M=7.3

18. True location of the source earthquake and rupture geometry • An earthquake in N. California • M=6.9

19. Importance of the slip distribution

20. Importance of the slip distribution • The stress change computed on 2-D oop at 7.5 km depth. • Circles represent the M>4.0 aftershocks in the first year following the Landers event From Steacy et al. , 2004 JGR

21. Importance of the both rupture geometry and slip distribution • Neic : NEIC location, simple straight rupture plane with a mean slip • NEICtapc : tapered NEIC solution • simpflts : Wald’s rupture geometry with mean slip • surfrup : Mapped surface rupture with a mean slip • Wald : Wald and Heaton (1994) slip model • Bruno : Hernandez et al. (1999) slip model From Steacy et al. , 2004 JGR

22. Chen Ji, 2005 http://neic.usgs.gov

23. What would be the protocols for passing the results • About further 700 lives were lost due to the Duzce event • to end-users and • informing the public

24. Conclusions • Applying Coulomb stress technique for seismic hazard updating is feasible • Can be applied in near-real time (a time period ranging from 2 days to two weeks necessary depending on the studied region) • A coordination is needed • The protocol for passing the results is important

25. the Giant's Causeway, N. Ireland

27. ‘By combining the stress change map with the map of active faulting, likely locations for the occurrence of future earthquakes can be refined. Faults in the Izmit Bay area, the western part of Biga peninsula, the Saroz Gulf and a part of western Sea of Marmara must be regarded as posing a specific hazard.’ From Nalbant et al. , 1998 JGR