The 2010 RESIS-II Seismic Hazard Model for Central America

As part of the RESIS-II cooperation project a PSHA model has been developed by a seismic-hazard team from Costa Rica, Guatemala, Honduras, Nicaragua, el Salvador, Panama, Norway and Spain (Benito et al., 2010, 2012). In this context a parametric earthquake catalog for the region was compiled and homogenized to moment magnitude, Mw. The seismotectonic models proposed in the previous phase (RESIS-I) were revised and two seismogenic zonations proposed (see details below). After a comparison with local strong motion data (statistical analysis of residuals) a set of GMPEs associated with the tectonic regimes present in the region (active shallow crust, volcanic, subduction interface, and subduction intraslab) were defined.

The original seismic hazard calculation was made using CRISIS2007 code in a grid of 0.1 x 0.1 degrees (aprox 10 km), for return periods of 200, 1000, and 2500 years. As a result, maps in terms of peak ground acceleration (PGA) and spectral accelerations SA (T) for periods of 0.1, 0.2, 0.5, 1, and 2s were obtained, as well as uniform hazard spectra (UHS) for six major cities of the region.

Based on the catalogue proposed by Rojas et al. (1993), and with the contribution of data and experts from each country, a regional parametric catalog covering the last 500 years was created. The revision and depuration process was made using local experts following an “expert criteria scheme”. The magnitude was homogenized to Mw, using local conversion relations (see Benito et al., 2010) and the completeness analysis was made following the Stepp (1973) method. In Benito et al. (2012) a reference is made to the declustering analysis, but a detailed information about how it was made is not included.

Following the major tectonic structures in the region:

• The subduction zone in the plate boundary Cocos –Caribbean,
  
• The volcanic chain (the faults related to),
  
• The Polochic – Motagua transform fault in the North America – Caribbean plate boundary,
  
• The Panamá fracture zone in the Cocos–Nazca boundary and
  
• The north Panamá deformed belt.
  

A regional seismogenic zonation with three tectonic regimes (active shallow crustal, subduction interface, and subduction intraslab) was defined. All the source zones were defined as area sources. The crustal zones (h ≤ 25 km) have been modeled with a 2D geometry, while a 3D geometry was considered for interface (25 km < h ≤ 60 km) and intraslab source zones (h > 60 km), with exception of the interface zone related to the north Panamá belt (flat zone at 50km of depth). A detailed description of the source zones is included in Benito et al. (2010).

The PSHA model is implemented using basically the information published in Benito et al. (2012). The source model is implemented in a unique source model file in NRML format representing the different typology and tectonic region type defined in the original model. In the active shallow crust the source zones are modelled as NRML areaSource, while in the subduction region the source zones are modelled as NRML complexFaultSource representing both, interface and intraslab sources.

The map below depicts the annual occurrence rate per source (between minimum and maximum magnitudes) for the different source models included in the hazard model. Click the show map layers icon to view different source models and base layer maps.

After a preliminary selection of GMPEs developed from tectonic environments similar to those of Central America, an analysis of residuals following the criteria proposed by Scherbaum et al. (2004) and using local strong motion data were made. The models that better fit the local data were used in the hazard calculation as a logic tree with four major branches:

The site condition is defined using the Vs30 value in the GMPEs having this parameter as predictor variable (YOU97 and ZHA06), the remaining GMPE (CLI94) is used with coefficients already calibrated for rock conditions.

The calculation is made using the combination proposed in Benito et al.(2010) and hazard curves and maps are obtained. The figures below represent hazard curves for peak ground acceleration, for 10% probabilities of exceedance in 50 years, using the OpenQuake-engine and CRISIS for the major cities in the region. The black lines represent the results obtained in a single branch, while the red and blue ones are the mean curves from the OpenQuake-engine and CRISIS respectively. The agreement between the original results and the implemented ones is more than acceptable as seen in the figures.

The following are mean hazard maps, for 9.52% probability of exceedance in 50 years, computed with the OpenQuake-engine and CRISIS. The maps confirm a good agreement between the original and implemented models. However, a map showing the absolute difference gives a more detailed and quantitative picture of the differences. The largest ones are located along the Guatemala and El Salvador coast and are associated with the subduction interface sources and the different approaches used to model the earthquake ruptures in the OpenQuake-engine and CRISIS. It is worth noticing that differences in the implementation of Zhao et al. (2006) in CRISIS and the OpenQuake-engine for low/median magnitude values were found. Further analysis is required to better constrain what are the sources of the discrepancies.

• Benito, B., C. Lindholm, E. Camacho, Á. Climent, G. Marroquín, E. Molina, W. Rojas, E. Talavera, J. J. Escobar, G. Alvarado, Y. Torres, and M. Perez-Escalante (2010). Amenaza sísmica en América Central, Benito Oterino, M. B., and Y. Torres Fernández (Editors), Entimema, Madrid, Spain, 371 pp. (in Spanish).
  

• Benito M.B., Lindholm C., Camacho E., Climent Á., Marroquín G., Molina E., Rojas W., Escobar J.J., Talavera E., Alvarado G.E., Torres Y., 2012. A New Evaluation of Seismic Hazard for the Central America Region. Bulletin of the Seismological Society of America, 102, 2, 504-523, doi:10.1785/0120110015 © Journal article
  

• Climent, Á, W. Taylor, M. Ciudad Real, W. Strauch, M. Villagran, A. Dahle, and H. Bungum (1994). Spectral strong motion attenuation in Central America, NORSAR Technical Report No. 2-17, 46 pp.
  

• Rojas W., H. Bungum and C. Lindholm (1993): Historical and recent earthquakes in Central America. Rev. Geol. Amer. Central, Vol. 16, pp. 5-21. Article

• Scherbaum, F., Cotton, F. and Smit, P. (2004). On the Use of Response Spectral-Reference Data for the Selection and Ranking of Ground-Motion Models for Seismic-Hazard Analysis in Regions of Moderate Seismicity: The Case of Rock Motion. Bulletin of the Seismological Society of America. 94:6, 2164-2185. Journal article

• Stepp, J. C. (1973). Analysis of completeness of the earthquake sample in the Puget Sound area, in S. T. Harding (Editor). Contributions to seismic zoning, U.S. National Oceanic and Atmospheric Administration Technical Report ERL 267-ESL 30, Washington, D.C., 16–28.
  

• Wells, D.L., and Coppersmith, K.J., 1994, New empirical relationships among magnitude, rupture length, rupture width, and surface displacements: Bulletin of the Seismological Society of America, v. 84, p. 974–1002. Journal Website

• Youngs, R.R., Chiou, S.J., Silva, W.J., and Humphrey, J.R. (1997). Strong ground motion attenuation relation-ships for subduction zone earthquakes. Seismological Research Letters, 68(1), pp.58-73. Journal article
  

• Zhao, J. X., J. Zhang, A. Asano, Y. Ohno, T. Oouchi, T. Takahashi, H. Ogawa, K. Irikura, H. K. Thio, P. G. Somerville, Yasuhiro Fukushima, and Yoshimitsu Fukushima (2006). Attenuation relations of strong ground motion in Japan using site classification based on predominant period, Bull. Seismol. Soc. Am. Vol. 96, No. 3, pp.898–913. Journal website
  

This table summarises the main characteristics of the original implementation of this model

The OpenQuake-engine input model (NRML format) can be downloaded at the link provided below - Please read the license and disclaimer attached to the model.

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