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

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.

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

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

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

Chen Ji, 2005

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,… ’ From McCloskey et al., 2005 Nature Published 17 March 2005

Is it a feasible method?

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

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

Coulomb stress formulation §From slip distribution l Compute stress tensor Resolve into Coulomb stress

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

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

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

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

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

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

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

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

Chen Ji, 2005

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

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

the Giant's Causeway, N. Ireland

From Nalbant et al., 1998 JGR ‘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.’