1. 26 July 2013 Símon Ólafsson, EERC
Scientific aspects of
South Iceland earthquakes
26 July 2013
Símon Ólafsson, EERC

2. UPStrat MAFA: 3rd General Meeting in Selfoss, July 23-26, 2013
Outline
Introduction
Icelandic Strong Motion Network
Estimation of source parameters
Ground motion prediction equation (GMPE)
Discrete time realization
Conclusions
UPStrat MAFA: 3rd General Meeting in Selfoss, July 23-26, 2013

3. Historical earthquakes in the SISZ
UPStrat MAFA: 3rd General Meeting in Selfoss, July 23-26, 2013

4. Icelandic Strong Motion Network
UPStrat MAFA: 3rd General Meeting in Selfoss, July 23-26, 2013

5. Árborg Town Hall: The strong-motion array
UPStrat MAFA: 3rd General Meeting in Selfoss, July 23-26, 2013

6. The Árborg Town Hall: Earthquake 29 May 2008, UTM 15:45
UPStrat MAFA: 3rd General Meeting in Selfoss, July 23-26, 2013

7. Internet Site for the European Strong motion Database (ISESD)
UPStrat MAFA: 3rd General Meeting in Selfoss, July 23-26, 2013

8. Recent earthquakes in South Iceland
Mw 6.0, 25 May 1987
Mw 6.5, 17 June 2000
Mw 6.5, 21 June 2000
Mw 6.3, 28th May 2008
UPStrat MAFA: 3rd General Meeting in Selfoss, July 23-26, 2013

9. Ground motion model (Stochastic method)
UPStrat MAFA: 3rd General Meeting in Selfoss, July 23-26, 2013

10. Selection of S-wave window
UPStrat MAFA: 3rd General Meeting in Selfoss, July 23-26, 2013

11. Estimation of parameters
Ds stress drop
k = R/Qb ‘spectral attenuation’
M0 seismic moment
Moment magnitude Mw (Hanks-Kanamori):
UPStrat MAFA: 3rd General Meeting in Selfoss, July 23-26, 2013

12. Earthquake 28 May 2008 - Parameters
Parameter Estimate Units
_____________________________________
Mo × N m Mw
Fc Hz
r km
k s
Ds × Pa
u cm
UPStrat MAFA: 3rd General Meeting in Selfoss, July 23-26, 2013

13. Attenuation of PGA South Iceland June 2000
UPStrat MAFA: 3rd General Meeting in Selfoss, July 23-26, 2013

14. Geometric spreading function
d = epicentral distance
h = depth parameter
D1, D2 and D3 are used to set the limits for the different zones of the spreading function
UPStrat MAFA: 3rd General Meeting in Selfoss, July 23-26, 2013

15. UPStrat MAFA: 3rd General Meeting in Selfoss, July 23-26, 2013
Derivation of GMPE
Parseval theorem:
PGA (amax) related to rms-acceleration (arms) with peak factor (p):
amax = parms
UPStrat MAFA: 3rd General Meeting in Selfoss, July 23-26, 2013

16. UPStrat MAFA: 3rd General Meeting in Selfoss, July 23-26, 2013
Theoretical GMPE
UPStrat MAFA: 3rd General Meeting in Selfoss, July 23-26, 2013

17. UPStrat MAFA: 3rd General Meeting in Selfoss, July 23-26, 2013
Attenuation for 29 May 2008
UPStrat MAFA: 3rd General Meeting in Selfoss, July 23-26, 2013

18. UPStrat MAFA: 3rd General Meeting in Selfoss, July 23-26, 2013
Duration estimation
a) Duration based on 90% cumulative energy. The dotted red curve represent mean value +/- one standard deviation (+/-1s). b) The curves represent the duration function of Eqn for different fractions of total cumulative energy (50%, 55%, 60%, 65%, 70%, 75%, 80%, 85% and 90%).
UPStrat MAFA: 3rd General Meeting in Selfoss, July 23-26, 2013

19. Ground motion simulation
UPStrat MAFA: 3rd General Meeting in Selfoss, July 23-26, 2013

20. Discrete time realizations
Time domain equations for sub-filters representing discrete model.
Sub-filter
Time domain discrete representation
Brune H1
Savage H2 H3 H4
UPStrat MAFA: 3rd General Meeting in Selfoss, July 23-26, 2013

21. UPStrat MAFA: 3rd General Meeting in Selfoss, July 23-26, 2013
Conclusions
For the South Iceland earthquakes the near-field attenuation has a high rate of attenuation (R-2)
Ground motion model (GMPE) has to include a geometrical attenuation term to accound for the fast rate of attenuation in the near-field
GMPE based on a physical model can be applied to obtain ground motion parameters and for time series simulation
For realistic simulation of ground motion time sequences a realistic estimate of duration is important.
UPStrat MAFA: 3rd General Meeting in Selfoss, July 23-26, 2013

22. UPStrat MAFA: 3rd General Meeting in Selfoss, July 23-26, 2013

23. UPStrat MAFA: 3rd General Meeting in Selfoss, July 23-26, 2013
Introduction
Examine relationship: Modified Mercally Intensity (IMM) vs. g
UPStrat MAFA: 3rd General Meeting in Selfoss, July 23-26, 2013

24. UPStrat MAFA: 3rd General Meeting in Selfoss, July 23-26, 2013

25. Estimating parameters
PGA, PGV: Use for example larger og two horizontal component, average of peak values for horizontal
UPStrat MAFA: 3rd General Meeting in Selfoss, July 23-26, 2013

26. UPStrat MAFA: 3rd General Meeting in Selfoss, July 23-26, 2013
Intensities map
UPStrat MAFA: 3rd General Meeting in Selfoss, July 23-26, 2013

27. UPStrat MAFA: 3rd General Meeting in Selfoss, July 23-26, 2013