real-time application of coulomb stress modelling and related issues by suleyman s. nalbant, sandy...
TRANSCRIPT
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? 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.’
Published17 September 1999
From Barka, 1999, Science
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
Published17 March 2005
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 Compute stress tensor
nCFF
• 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
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
0,00%
10,00%
20,00%
30,00%
40,00%
50,00%
60,00%
70,00%
80,00%
90,00%
0 0,1 0,2 0,3 0,4 0,5 0,6 0,7 0,8 0,9
coefficient of friction
% f
oca
l m
ech
anis
ms
wit
h p
os.
str
ess
hernandez
wald
simpflts
surfrup
neictapc
neic
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
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.’