1. Dr. Praveen K. Malhotra, P.E.
Ground Motion Histories for Seismic Design of Kingdom Tower in Saudi Arabia
Contact Information:
Dr. Praveen K. Malhotra, P.E.
SEAOA Convention, Tucson, Arizona
June 18-20, 2015

2. Outline
Engineering Perspective of Probabilistic Seismic Hazard Analysis (PSHA)
Ground Motion Histories for Seismic Design of Kingdom Tower in Saudi Arabia

3. Overview
Structural
Geotechnical
Seismological
Geological

4. Where Will Future Earthquakes Occur?

5. Where Will Future Earthquakes Occur?

6. How Big Will They be and When Will They Occur?
Mw 794 years MRI
Mw 977 years MRI
Mw 1202 years MRI
Mw 1479 years MRI
Mw 1820 years MRI
Mw 2240 years MRI

7. How Strong Will the Ground Shake During a Magnitude M 7
How Strong Will the Ground Shake During a Magnitude M 7.5 Earthquake at 20 km?

8. How Strong Will the Ground Shake During a Magnitude M 7
How Strong Will the Ground Shake During a Magnitude M 7.5 Earthquake at 20 km?

9. Probabilistic Seismic Hazard Analysis
Geological and seismological models are so uncertain that only probabilistic predictions can be made regarding ground shaking

10. Peak Ground Acceleration Hazard Curve for a Site in Los Angeles

11. Maximum Acceleration in 50 Years
µ = g
= g
COV = /µ = 1.01

12. Geographical Variation of Uncertainty
City
µ (g)
 (g)
COV = /µ
Los Angeles
0.208
0.21
1.01
San Francisco
0.189
0.9
Memphis
0.083
0.177
2.15
Boston
0.023
0.07
3.11

13. Why Does Uncertainty Matter?

14. Expected and Design Acceleration
µPGA = g
DesignPGA = g

15. Expected and Design Accelerations for Different Cities
City
Expected (g)
Design (g)
Design/Expected
Los Angeles, CA
0.208
0.536
2.6
San Francisco, CA
0.21
0.514
2.4
Memphis, TN
0.0669
0.345
5.2
Boston, MA
0.0226
0.0946
4.2
Uncertainty increases the cost of mitigation

16. Uncertainty increases the cost of insurance
Return Period of Collapse for Same Ratio Between Expected and Design Accelerations
City
MRP of Collapse
Los Angeles, CA
4250 years
San Francisco, CA
5000 years
Memphis, TN
1500 years
Boston, MA
2200 years
Uncertainty increases the cost of insurance

17. Design Versus Expected Annual Acceleration
City
Expected (g)
Design (g)
Design/Expected
Los Angeles, CA
0.0113
0.536 47
San Francisco, CA
0.0108
0.514 48
Memphis, TN
0.345
163
Boston, MA
0.0946
178
Uncertainty makes mitigation less attractive than insurance

18. Effects of Uncertainty
Increased cost of mitigation
Increased cost of insurance
Voluntary mitigation becomes less attractive compared to insurance, but insurance cannot reverse:
Loss of life
Loss of business
Damage to environment
Insurance without mitigation is costly

19. Historic Variation of Uncertainty 50-year Maximum PGA
COV = /µ
1996
0.25
0.188
0.75
2002
0.258
0.2
0.78
2008
0.234
0.221
0.95
2014
0.208
0.21
1.01
Geoscientists are less certain now than in 1996

20. Reasons for Increased Uncertainty
As computers became faster and more powerful, it became possible for the USGS to consider more sources of uncertainty in the PSHA
The number of opinions regarding the geological and seismological models increased over the years due to a greater number of researchers investigating the seismic hazard
Seismic hazard analysis is in its early stages and geoscientists are still discovering more and more that they do not know

21. Significance of Change Between the Results of Successive PSHA
Effect size, d = (µ1 - µ2)/
d > 0.8 is large change
d ~ 0.5 is moderate change
d < 0.2 is small change
Cohen, J. (1988). Statistical Power Analysis for the Behavioral Sciences (second ed.), New Jersey, Lawrence Erlbaum Associates.

22. Significance of Change Between the Results of Successive PSHA
Interval
Effect-Size of Change
0.04
0.11
0.12
Changes in ground motion predictions were statistically insignificant

23. Suggestions to Avoid Misuse of PSHA
PSHA should not be considered as an excuse for using models with high uncertainty. Models with high uncertainty increase the costs of mitigation and insurance. There is a common misconception that uncertainty does not matter as long as it can be modeled in the PSHA

24. Suggestions to Avoid Misuse of PSHA
The focus in seismic hazard analysis should shift from considering uncertainty to reducing uncertainty. In the seismic hazard community, there are more discussions on considering uncertainty, and practically no discussions on reducing uncertainty. The real progress in the science of ground motion prediction can only be made by reducing uncertainty

25. Suggestions to Avoid Misuse of PSHA
Uncertainty in geological and seismological models should be reduced by gradually replacing empirical models with physics-based models and by limiting the number of opinions considered in the PSHA. Empirical models, by their very nature, are uncertain and there are several opinions regarding empirical models. For example, at present time, there are about 300 ground motion prediction models in the published literature.

26. Suggestions to Avoid Misuse of PSHA
The design ground motions should not be revised unless a statistically significant change occurs in the predicted ground motions. The uncertainty in ground motion prediction is so high that a slight changes in ground motion estimates do not justify a change in the design ground motions

27. Suggestions to Avoid Misuse of PSHA
Site-specific PSHA should not be used for the sole purpose of reducing design ground motions. Since there are many opinions regarding geological and seismological models, a combination of opinions can be easily found which provides a lower estimate of the design ground motion. This practice should be stopped, because it provides a biased assessment of the risk

28. Suggestions to Avoid Misuse of PSHA
Same predictions of ground motions should be used for seismic design and insurance of all types of structures. There is no convincing argument for separate PSHA for buildings, bridges, dams and nuclear power plants. Design ground motions should be different for different types of structures, based on the consequence of damage; but the underlying assessment of the hazard should be the same

29. Suggestions to Avoid Misuse of PSHA
Seismic hazard models should not be made more complex unless they reduce uncertainty. It does not make sense for ground motion prediction models to become more complex and less certain at the same time. Complexity without certainty is self-serving

30. Ground Motion Histories for Seismic Design of Kingdom Tower

31. Seismic Map of Region According to USGS
Kingdom Tower

32. Propagation of High- and Low-Frequencies

33. 2475-year MRP Response Spectrum from PSHA by Langan International

34. Earthquake Scenarios Controlling the Seismic Hazard
Natural Period, T (s)
Magnitude, Mw
Distance (km)
0.3
5.9 70
 4
7.1
1000

35. Long-Period Transition for Different Magnitude Earthquakes (NEHRP 2003)
Magnitude Mw
TL (s)
6.0 – 6.5 4
6.5 – 7.0 6
7.0 – 7.5 8
7.5 – 8.0 12
8.0 – 8.5 16
8.5 – 9.0+ 20

36. 2475-year MRP Response Spectrum

37. Target Response Spectrum for Closer-Smaller Earthquakes

38. Target Response Spectrum for Distant-Larger Earthquakes

39. Vertical Response Spectra for Closer and Distant Earthquakes

40. ‘Seed’ Ground Motion for Closer Earthquake Scenario

41. Response Spectra of ‘Seed’ Ground Motion for Closer Earthquake Scenario

42. Response Spectra of Modified Horizontal Components

43. Response Spectra of Modified Horizontal and Vertical Components

44. Comments
High-rise buildings respond to ground displacements rather than ground accelerations
Site-specific free-surface ground motions do not depend on the structure being analyzed; they depend only on the geology and seismology of the region
All three components of a ground motion need to be simultaneously modified to make it site-specific