A Brief Review on Akkar, Sandikkaya and Bommer

(ASB13) GMPE

Sinan Akkar Department of Civil Engineering, Middle East

Technical University 06800 Ankara, Turkey

Southwestern U.S. Ground Motion Characterization Senior Seismic Hazard Analysis Committee – Level 3 Workshop #2 – October 22-24, 2013

Outline

o Overview of ASB13 with emphasis on o Magnitude dependence of sigma

o Reduction in sigma after 3 seconds

o Dependence of residuals on depth

o Normal faulting factors

Sinan Akkar – 23/10/2013

Major features of ASB13

Sinan Akkar – 23/10/2013

o Developed using a subset of RESORCE (Reference Database for Seismic-Ground Motion in Europe)

o Total number of earthquakes: 221 o Total number of records: 1041 o Minimum and maximum response periods: PGA, PGV and T = 0.01s – T = 4.0s o Horizontal component definition: Geometric mean o Distance metrics: Repi, Rhyp and RJB o Maximum distance: 200 km o Maximum depth: 30 km o Minimum and maximum moment magnitude: Mw 4 – Mw 7.6 o Minimum and maximum VS30 (all measured): VS30 = 92 m/s – VS30 = 2165 m/s o Recommended magnitude, distance, period and VS30 intervals:

o 4 ≤ Mw ≤ 8 o Distances up to 200 km o PGA, PGV and 0.01s ≤ T ≤ 4 s o 150 m/s ≤ VS30 ≤ 1200 m/s

Overall distribution of strong-motion database

o 3-component, 1041 recordings with distances less than 200 km

o 221 earthquakes (MS + AS) with focal depths less than 30 km and Mw ≥ 4.

o Each event has at least 2 recordings

o 322 stations with measured VS30 values.

o Magnitudes up to Mw 7 and distances RJB > 5 km are well represented

Sinan Akkar – 23/10/2013

RJB (km)

1 10 100

Mw

4

5

6

7

8

SoF and VS30 – based distribution of strong-motion database

o Few data with VS30 > 800 m/s and VS30 < 180 m/s

o Reverse-faulting earthquakes are poorly represented. Most data come from normal (Italian) and strike-slip (Turkish) events

o Mw > 7 events are mostly from strike-slip earthquakes

Sinan Akkar – 23/10/2013

Depth distribution of strong-motion database

o Events with Mw > 6 have depths less than 20 km

o Depth distribution is more uniform for Mw ≤ 6

Sinan Akkar – 23/10/2013

Functional Form

[ ] [ ] tJBwREF SSoFRMYY εσ++= ln),,(ln)ln(

[ ]

[ ]

>++

+−++−+−+

≤++

+−++−+−+

=

198

26

2154

23171

198

26

2154

23121

)ln()()5.8()(aa

)ln()()5.8()(aa

)ln(

cMFaFaaRcMaaMacM

cMFaFaaRcMaaMacM

Y

wNR

JBWww

wNR

JBWww

REF

Median ground-motion for reference rock

Site effect

Aletory variability

Sinan Akkar – 11/07/2013

Style-of-Faulting (SoF) factors

o SoF coefficients are found to be sensitive to the distribution of faulting type in the database.

o They are obtained by removing the small events (Mw < 5) having less than 3 recordings (eliminate the poorly recorded events).

Period (s)

0.01 0.1 1

N:S

S

0.6

0.8

1.0

1.2

1.4

This studyAB10+BAD12AS08 BA08CB08CY08

Period (s)

0.01 0.1 1

R:S

S

0.6

0.8

1.0

1.2

1.4

Sinan Akkar – 23/10/2013 ZTOR is assumed as zero for AS08, CB08 and CY08

Fairly consistent pattern with CB08 and AB10

Very complicated patterns. No model is entirely compatible with the others

RJB (km)1 10 100

With

in-e

vent

Res

idua

ls

-2

-1

0

1

2

Mw

4 5 6 7 8

Bet

wee

n-ev

ent R

esid

uals

-1.0

-0.5

0.0

0.5

1.0

VS30 (m/s)100 1000

With

in-e

vent

Res

idua

ls

-2

-1

0

1

2

T = 0.0 s

RJB (km)1 10 100

Mw

4 5 6 7 8

VS30 (m/s)100 1000

T = 0.2 s

RJB (km)1 10 100

Mw

4 5 6 7 8

VS30 (m/s)100 1000

T = 1.0 s

Residual analysis – overall trends

o Data do not support magnitude-dependent sigma (sparse data sampling towards large magnitudes)

o No biased estimations in terms of distance

o Slight overestimation at very soft sites and under estimation for rock sites at short periods (e.g., T = 0.2s)

T = 0.0s T = 0.2s T = 1.0s

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4.0 4.5 5.0 5.5 6.0 6.5 7.0 7.5 8.0

Stan

dard

dev

iatio

n

0.0

0.2

0.4

0.6

0.8 Between-event residuals (T = 0.0s)

4.0 4.5 5.0 5.5 6.0 6.5 7.0 7.5 8.00.0

0.2

0.4

0.6

0.8 Between-event residuals (T = 0.2s)

4.0 4.5 5.0 5.5 6.0 6.5 7.0 7.5 8.00.0

0.2

0.4

0.6

0.8 Between-event residuals (T = 1.0s)

Mw

4.0 4.5 5.0 5.5 6.0 6.5 7.0 7.5 8.0

Stan

dard

dev

iatio

n

0.4

0.5

0.6

0.7

0.8 Within-event residuals (T = 0.0s)

Mw

4.0 4.5 5.0 5.5 6.0 6.5 7.0 7.5 8.00.4

0.5

0.6

0.7

0.8 Within-event residuals (T = 0.2s)

Mw

4.0 4.5 5.0 5.5 6.0 6.5 7.0 7.5 8.00.4

0.5

0.6

0.7

0.8 Within-event residuals (T = 1.0s)

Residual analysis – dependence of magnitude

Sinan Akkar – 23/10/2013

Variation of standard deviation seems to be independent of magnitude for Mw ≤ 6.5. For larger magnitudes, the fluctuations can be misleading as there is fewer data.

Residual analysis –magnitude and SoF dependence

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Sinan Akkar – 23/10/2013

Modeling uncertainty considering magnitude and SoF

PGA - Strike-Slip

RJB (km)1 10 100

Sig

ma

Mu

0.0

0.1

0.2

0.3

PGA - Reverse

RJB (km)1 10 100

0.0

0.1

0.2

0.3M4.0 M4.5 M5.0 M5.5 M6.0 M6.5 M7.0 M7.5 M8.0

PGA - Normal

RJB (km)1 10 100

0.0

0.1

0.2

0.3

p

RJB (km)1 10 100

Sig

ma

Mu

0.0

0.1

0.2

0.3

RJB (km)1 10 100

0.0

0.1

0.2

0.3M4.0 M4.5 M5.0 M5.5 M6.0 M6.5 M7.0 M7.5 M8.0

RJB (km)1 10 100

0.0

0.1

0.2

0.3

p

RJB (km)1 10 100

Sig

ma

Mu

0.0

0.1

0.2

0.3

RJB (km)1 10 100

0.0

0.1

0.2

0.3M4.0 M4.5 M5.0 M5.5 M6.0 M6.5 M7.0 M7.5 M8.0

RJB (km)1 10 100

0.0

0.1

0.2

0.3

Strike-slip Normal Reverse PGA

T=0.2s

T=1.0s

o No significant differences between normal and strike-slip earthquakes. Modeling uncertainty is higher for reverse events with respect to other two SoF

o More reliable results between 4.5 ≤ Mw ≤ 6

Residual analysis – depth dependence

Sinan Akkar – 23/10/2013

0 5 10 15 20 25 30

PG

A

-0.8-0.6-0.4-0.20.00.20.40.60.8

0 5 10 15 20 25 30-0.8-0.6-0.4-0.20.00.20.40.60.8

0 5 10 15 20 25 30-0.8-0.6-0.4-0.20.00.20.40.60.8

Depth (km)

0 5 10 15 20 25 30

T =

1.0s

-0.8-0.6-0.4-0.20.00.20.40.60.8

Depth (km)

0 5 10 15 20 25 30-0.8-0.6-0.4-0.20.00.20.40.60.8

Depth (km)

0 5 10 15 20 25 30-0.8-0.6-0.4-0.20.00.20.40.60.8

Normal Events Reverse Events Strike-Skip Events

0 5 10 15 20 25 30

T =

0.2s

-0.8-0.6-0.4-0.20.00.20.40.60.8

0 5 10 15 20 25 30-1.0-0.8-0.6-0.4-0.20.00.20.40.60.8

0 5 10 15 20 25 30-0.8-0.6-0.4-0.20.00.20.40.60.8

p = 0.087 p = 0.007 p = 0.339

p = 0.17 p = 0.011 p = 0.3

p = 0.25 p = 0.009 p = 0.48

Standard deviation

o Variation of sigma is almost period independent except for the portion between 3s and 4s.

o The level of total sigma is similar to AB10. It is slightly larger with respect to NGA-W1 GMPEs.

Period (s)

0.01 0.1 1

Stan

dard

dev

iatio

n

0.0

0.2

0.4

0.6

0.8

1.0

total

between-event

within-event

RJBRepi Rhyp

Sinan Akkar – 23/10/2013

Reduction in standard deviation after T = 3s

Sinan Akkar – 23/10/2013 Period (s)

0.01 0.1 1

Sta

ndar

d D

evia

tion

(for R

JB m

odel

)

0.2

0.4

0.6

0.8

1.0

Period (s)0 1 2 3 4

Dat

a Lo

ss (i

n %

)

0

10

20

30

40

AccelerogramsEarthquakes

between-event sigma

within-event sigma

total sigma

Considerable reduction in the data size for T ≥ 3s results in the observed decay in standard deviations

At T = 4s, 36% of accelerograms and 28% of earthquakes are removed due to low-cut filter values used in data processing.

Data loss doubles between T = 3s and T = 4s

Conclusions – 1/3 Magnitude-dependence of sigma (for larger earthquakes)

o Database contains few large magnitude events above Mw 7. Thus, the distribution of data does not allow establishing a magnitude-dependent sigma.

o The variation of standard deviation seems to be independent for Mw ≤ 6.5.

o The model uncertainty seems to be less significant for 4.5 ≤ Mw ≤ 6 for the whole distance range.

Influence of depth on ASB13 estimates

o The variation of between-event residuals in terms of depth indicate that the bias in normal and strike-slip ground-motion estimations is insignificant with respect to reverse events. The reverse fault ground motions tend to be overestimated with increasing depth.

Sinan Akkar – 23/10/2013

Conclusions – 2/3

How well the estimates are for different SoF?

o SoF coefficients show similarities with CB08 and AB10 for N:SS ratios. They differ significantly with the compared GMPEs for R:SS ratios. The database is rich in terms of normal and strike-slip earthquakes. It is believed that N:SS ratios are stable in our model.

o The insignificant Mw-dependent between-event residual trends for N and SS estimates indicate better performance of ASB13 for these faulting mechanisms. The same performance is not observed for reverse earthquakes

o The model uncertainty also seems to be less significant for normal and strike-slip events. This observation supports the stability of N:SS ratios (or stability of N and SS SoF coefficients).

Sinan Akkar – 23/10/2013

Conclusions – 3/3

Reduction in sigma after T = 3.0s

o The decrease in number of earthquakes and accelerograms results in a sudden drop in sigma after T = 3.0s.

o The within-event sigma seems to be affected more by the decrease in accelerograms after T = 3s

o The reduction in between-event sigma is observed only for T ≥ 3.8s due to decrease in event number.

Sinan Akkar – 23/10/2013

References

o Akkar S, Sandikkaya MA and Bommer J (2013). Empirical ground-motion models for point- and extended-source crustal earthquake scenarios in Europe and the Middle East. Bulletin of Earthquake Engineering, DOI 10.1007/s10518-013-9461-4

o Akkar S, Sandikkaya MA and Bommer J (2013). Erratum to: Empirical ground-motion models for point- and extended-source crustal earthquake scenarios in Europe and the Middle East. Bulletin of Earthquake Engineering, DOI 10.1007/s10518-013-9508-6

o Al Atik L and Youngs RR (2013). Epistemic uncertainty for NGA-West2 models. Pacific Earthquake Research Center, University of California at Berkeley, PEER Report 2013/11

Sinan Akkar – 23/10/2013

Thank you

Sinan Akkar – 23/10/2013