Realtime application of Coulomb stress modelling and related issues

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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

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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.

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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?

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Is it a feasible method?
Published 17 September 1999

• 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.

From Barka, 1999, Science
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Is it a feasible method?
From Parsons et al., 2000, Science
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Chen Ji, 2005
http//neic.usgs.gov
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Is it a feasible method?
Published 17 March 2005

• The results indicate that although a
  subduction-zone event in the Sunda trench has
  been made more likely by the SumatraAndaman
  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
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Is it a feasible method?
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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.

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What are the requirements for applying CST?

• True location of the source earthquake and
  rupture geometry
• Slip distribution
• A well-trained team

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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

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Coulomb stress formulation
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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
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Coulomb stress Calculations, Calculating s. on
3-D oop

• 2-D

• 3-D

• Regional stress

From McCloskey et al., 2003, GRL
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Coulomb stress Calculations, Calculating s. on
the mean structure
From McCloskey et al., 2003, GRL
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Coulomb stress Calculations, Calculating s. on
the structure
From McCloskey et al., 2005, Nature
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True location of the source earthquake and
rupture geometry

• An earthquake in S. California
• M7.3

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True location of the source earthquake and
rupture geometry

• An earthquake in N. California
• M6.9

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Importance of the slip distribution
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Importance of the slip distribution

• The stress change computed on 2-D oop at 7.5 km
  depth.
• Circles represent the Mgt4.0 aftershocks in the
  first year following the Landers event

From Steacy et al. , 2004 JGR
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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 Walds 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
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Chen Ji, 2005
http//neic.usgs.gov
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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

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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

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the Giant's Causeway, N. Ireland
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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
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