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Calibration of Strong-Motion Models for Central America Region

A. Climent1, B. Benito2, C. Lindholm3, D. Hernández4, C. Guzmán5 and J. M.Gaspar-Escribano2

1Depto. de Sismología y Vulcanología , Instituto Costarricense de Electricidad (ICE), San José, Costa Rica2 ETSI Topografía, Geodesia y Cartografía, Universidad Politécnica de Madrid, Madrid, Spain

3Seismology Department, NORSAR, Kjeller, Norway4Servicio Nacional de Estudios Territoriales (SNET), San Salvador, El Salvador

5Instituto Nicaraguense de Estudios Territoriales(INETER), Managua, NicaraguaEmail: acliment@ice.go.cr, ma_ben@topografía.upm.es, conrad@norsar.no, dhernandez@snet.gob.sv, carlos.guzman@gf.ineter.gob, jgaspar@topografía.upm.es

ABSTRACTWe present the results of a study aimed at selecting the more suitable strong-motion models for seismic hazard analysis in the Central America (CA)Region. After a careful revision of the state of the art, different models developed for subduction and volcanic crustal zones, in tectonic environmentssimilar to those of CA, were selected. These models were calibrated with accelerograms recorded in Costa Rica, Nicaragua and El Salvador. The peakground acceleration (PGA) and spectral accelerations SA (T) derived from the records were compared with the ones predicted by the models in similarmagnitude, distance and soil conditions. Corrections for type of magnitude (Ms, Mb, Mw), distance (Rhyp, Rrup, etc) and ground motion parameter (maximumhorizontal component, geometric mean, etc) were taken into account in the comparisons with actual data. As result of the analysis, the models whichpresent the best fit with the local data were identified. These models have been applied for carrying out a seismic hazard analysis in the region, in theframe of the RESIS II project financed for the Norwegian Cooperation Agency (NORAD).

KEYWORDS: Central America, accelerograms, ground motion, spectral acceleration, seismic hazard

Tectonic environment

Scenarios with different attenuation

Equation Data base

Parameter component (PGA, Sa)

Source type Distance (km) Mw

Youngs et al.(1997) (YOUN97) World Geometrical

mean Inslab Interface 10 – 500 5,0 - 8.2

Atkinson and Boore 2003

(AYB03)World Aleatory (both

horizontal) Inslab Interface 10-400 5,0 - 8,3

Garcia et al.(2005) (GAR05) Mexico Quadratic

mean Inslab 4 – 400 5,2 - 7,4

Cepeda et al.(2004) (CEP04)

El Salvador

Random(geometrical

mean)

Inslab Shallow crust

10 – 4000-100

5,0 - 8,35,1- 7,2

Climent et al.1994 (CLI94)

Central America Mexico

LargestHorizontal

Interface Shallow crust 5 - 400 4,0 - 8,0

Zhao et al. (2006) (ZH06) Japan Geometrical

meanInterface, inslab,

shallow crust 10-300 5,0 - 8,2

Spudich et al.(1999) (SEA99) World Geometrical

mean Shallow crust 0 - 100 5,1 - 7,2

Schmidt et al.(1997) (SCH97)

Costa Rica

LargestHorizontal Shallow crust 6 - 200 3,7- 7,6

3

4

5

6

7

8

0 100 200 300 400 500

Hypocentral distance (km)

Mom

ent m

agni

tude

(Mw

)

3

4

5

6

7

8

0 50 100 150 200 250

Focal depth (km)

Mom

ent m

agni

tude

(Mw

)

Selected ground motion models Strong motion data used for calibration of models

Contrast of Models: Analysis of Residuals

A ground-motion database containing instrumental data from Central America was used for contrasting observations and predictions of ground-motion models developed for other regions with seismotectonic affinity to Central America.

The following conclusions can bedrawn:

- For shallow crustal sources, theuse of models ZH06, CLI94 andSEA99 as well as of models SCH97and CEP04 is recommended.

- For subduction interface sources,the use of models ZH06 and YOUN97is recommended.

- For inslab subduction sources,models ZH06, SEA99 and GAR05 isrecommended.

0.001

0.01

0.1

1

1 10 100 1000Distancia (km)

PG

A (g

)

Zhao et al., 2006

Climent et al., 1994

PGA

0.001

0.01

0.1

1

10 100 1000

Distancia (km)

PG

A (g

)

Youngs et al., 1997

0.001

0.01

0.1

1

10

10 100 1000

Distancia (km)

PGA

(g)

Zhao et al., 2006

Youngs et al., 1997

PGA

Mw 7.0

Mw 6.0

Mw 5.0

Summary and conclusions

Distribution of Mw versus distance (left) and focal depth (right)

Amount of seismic events and records supplied by each country (complete data base)

REFERENCES

- Atkinson, G. and Boore, D.M. (2003). Empirical ground-motion relations for subduction-zone earthquakes and theirapplication to Cascadia and other regions. BSSA,Vol. 93, No.4,pp. 1703-1729.- Cepeda, J. M., Benito, B. and Burgos, E. A. (2004). Strong Motion Characteristics of January and February, 2001Earthquakes in El Salvador. In: Natural Hazards in El Salvador GSA Special Paper, vol. 75, pp. 375-25.- Climent, A., Taylor, W., Ciudad Real, M., Strauch, W., Villagran, M., Dahle, A. and Bungum, H. (1994). Spectral strongmotion attenuation in Central America. NORSAR. Technical Report No. 2-17. 46 pp.- García, D., Singh S. K., Herráiz, M., Ordaz, M. and Pacheco J.F. (2005). Inslab earthquakes of Central México: Peakground-motion parameters and response spectra. Bull. Seism. Soc. Am., vol. 95, No.6, pp. 2272-2282.- Schmidt, V., Dahle, A. and Bungum, H. (1997). Costa Rican Spectral Strong Motion Attenuation. NORSAR, TechnicalReport. 45 pp.

Central America is located in the western limit of the Cocos plate. This plate is surrounded by the North American, Caribbean, Nazca and South Americanplates. Regarding the attenuation of ground motion, we can distinguish three tectonic environments: crustal zones, subduction interface and subductioninslab zones, since the effects of the wave propagation led to different attenuation of energy with distance in the three sources.

Crustal events

Example of residuals distribution: PGA residuals vs. distance for subduction inslab events.

The goodness of fit of a model to the data is represented by the % of recorded data which residuals are within the (mean 1σ) interval. Residuals are defined as:ln(PGAobserved) – ln (PGApredicted).The Table indicates these % of observations for each model and scenario considered.

Financed by:

Other participants:

PGA SA PGA SA PGA SAInterface 8 54 30 11 45 7 8 75 0

Inslab 7 60 18 12 56 8 14 149 12shallow crust 13 107 107 12 61 60 16 74 26

# events

El SalvadorNicaraguaCosta Rica# records# records# records# events # events

h < 25 km

Shallow seismicity

Subduction interface25<h≤60 km

Intermediate seismicity

Subduction inslabh>60 km

Deep seismicity

- Spudich, P., Joyner, W. B., Lindh, A. G., Boore, D. M., Margaris, B. M., Fletcher, J. B. (1999) SEA99: A revisedground motion prediction relation for use in extensional tectonic regimes. Bull. Seism. Soc. Am., vol. 89, No. 5, pp.1156-1170.- Youngs, R. R., Chiou, S. J., Silva, W. J. and Humphrey, J. R. (1997). Strong ground motion attenuationrelationships for subduction zone earthquakes, Seism. Res. Lett., vol. 68, No. 1, pp. 58-73.- Zhao, JX, Zhang, J.,Asano, A., Ohno,Y., Oouchi, T.,Takahashi, T., Ogawa, H., Irikura, K., Thio, H.K. andSomerville, P.G. (2006). Attenuation Relations of Strong Ground Motion in Japan Using Site Classification Basedon Predominant Period, Bull. Seism. Soc. Am., Vol 96, pp.898-913.

PGA PSA

Shallow Inslab Interface Shallow Inslab Interface

1σ 1σ 1σ 1σ 1σ 1σCEP04 45 37 37SEA99 36 49SCH97 60 59ZH06 50 65 57 51 70 47CLI94 46 48 55 46

YOUN97 74 64 57 39

AYB03 25 29 22 68GAR05 50 52