# Arabian Peninsula (ARB)

### Authors:

H. Zahran, V. Sokolov, S. El-Hadidy Youssef, W. W. Alraddadi, M. J. Roobol, I. C. F. Stewart, M. El-Hadidy

For any additional information about this model please contact: Zahran.HM@sgs.org.sa

## Summary

The 2018 seismic hazard model of the Arabian Peninsula (ARB) was developed by the Saudi Geological Survey (SGS). The model covers Saudi Arabia, Yemen, Oman, and Qatar. The model has been translated into the OpenQuake (OQ) engine format by GEM.

Information about the OQ model versions and input files can be found on the Results and Dissemination page.

## Interactive Viewer

The viewer below depicts the seismic sources and hazard results in terms of PGA for a return period of 475 years. Click on the menu in the upper right corner to select the layer.

## Tectonic overview

The Arabian Peninsula is a microcontinent on its own tectonic plate in between southern Eurasia and Africa. The plate moves northward relative Eurasia at ~20 mm/yr, resulting in continental convergence and thrust faulting within the Zagros and eastern Anatolian fold belts to the north (which to the southeast continues as subduction of oceanic crust under Iran and western Pakistan), and left-lateral strike-slip faulting along the Dead Sea Transform in the east. To the south, Arabia is moving away from northeastern Africa, leading to oceanic spreading centers in the Red Sea and Gulf of Aden; these form two sides of a ridge-ridge-ridge triple junction with the third branch as the East African Rift extending south.

## Basic Datasets

Input datasets used for the development of the ARB model are property of the Saudi Geological Survey (SGS). The seismic source model for Arabian Peninsula has been constructed on the basis of recent studies related to seismic hazard assessment for the region. See Al-Arifi et al. 2013, Mohindra et al. 2012, Sokolov et al. 2017, Zahran et al 2016 for a description of the datasets used for developing the hazard model.

## Hazard Model

### Seismic Source Characterisation

The Seismic Source Characterization (SSC) model consists of 29 homogeneous area source zones (Figure 1) for which seismicity parameters (occurrence, maximum magnitude, depth distribution) and dominant faulting style have been determined. The two models differ only by the occurrence parameters.

The OQ engine implementation of the SSC
uses the OQ source typology **Area Source**. The sources are depicted in the
interactive viewer below.

**Figure 1 -** *The 29 seismic zones of the source model for the Arabian Peninsula.*

#### Epistemic Uncertainties

Since two different declustering approaches (Gardner and Knopoff, 1974 and Uhrhammer 1986) have been applied to the original earthquake catalogue data, two alternative source models are made available in the logic-tree to account for epistemic variability.

### Ground Motion Characterisation

The Ground Motion Characterization (GMC) model contains 7 ground motion prediction equations (GMPE). The Atkinson and Boore model (2006) is used for the stable continental region of Saudi Arabia in conjunction with the equations for active shallow crustal sources, namely: the models of Zhao et al. (2006), Boore and Atkinson (2008), Campbell and Bozorgnia (2008), and Akkar et al. (2014). The largest weight (0.60) is assigned to the Atkinson and Boore model for stable regions and equal weights (0.10) are assigned for crustal source equations. Akkar et al. (2014) suggested to consider their model for seismic hazard studies in areas where normal-faulting earthquakes dominate. Therefore, the model (weight 0.3) was used together of Pankow and Pechmann (2004) model (weight 0.7) for extensional zones in the Red Sea. The Pankow and Pechmann’ model supersedes a previous study of strong ground motions in extensional tectonic regimes by Spudich et al. (1999).

Two GMPEs developed for the volcanic region of Hawaii were used specifically for the volcanic areas (Yemen Basaltic Trap, Harrat Lunayyir Hot Spot, Makkah- Madinah-Nafud) seismic source zone. The first model is the equation obtained by Munson and Thurber (1997) on the basis of earthquake records from 22 shallow earthquakes with magnitudes from 4.0 to 7.2. The equation predicts PGA as a function of magnitude and source-to-site distance for two site conditions – lava and ash. The maximum of two horizontal components was considered in the model, therefore a coefficient 1.1 (Beyer and Bommer, 2006) is applied in our calculation for conversion to geometric mean of horizontal components that is used in all other GMPEs used in this work. The second equation was developed by Atkinson (2010). Note that the Munson and Thurber model is used for PGA, the Atkinson model for response spectra.

**Figure 2 -** *Comparison of the ground motion predicted by the different GMPEs
used in the ARB model. The plot is for spectral acceleration at 0.2 seconds and
Mw 6.*

The table below shows the GMC. While in the original implementation the different GMPE were defined by source, in the OQ engine the GMPEs have been clustered into four main tectonic groups: stable regions (TECTONIC_REGION_1), the Red Sea (TECTONIC_REGION_2), active shallow crust (TECTONIC_REGION_3), and volcanic (TECTONIC_REGION_4). The groups are also depicted in Figure 3. Two GMPE logic- trees are implemented, one for PGA and one for other spectral ordinates.

#### Epistemic Uncertainties

For every tectonic region, epistemic uncertainty is considered by using multiple GMPEs, each with an associated logic tree weight.

TECTONIC_REGION_1 |
Weight |

AtkinsonBoore2006SGS | 0.6 |

AkkarEtAlRjb2014 | 0.1 |

BooreAtkinson2008 | 0.1 |

CampbellBozorgnia2008 | 0.1 |

ZhaoEtAl2006AscSGS | 0.1 |

TECTONIC_REGION_2 |
Weight |

PankowPechmann2004 | 0.7 |

AkkarEtAlRjb2014 | 0.3 |

TECTONIC_REGION_3 |
Weight |

AkkarEtAlRjb2014 | 0.25 |

BooreAtkinson2008 | 0.25 |

CampbellBozorgnia2008 | 0.25 |

ZhaoEtAl2006AscSGS | 0.25 |

TECTONIC_REGION_4 |
Weight |

MunsonThurber1997 (PGA), Atkinson2010Hawaii (SA) | 0.3 |

AtkinsonBoore2006SGS | 0.3 |

AkkarEtAlRjb2014 | 0.1 |

BooreAtkinson2008 | 0.1 |

CampbellBozorgnia2008 | 0.1 |

ZhaoEtAl2006AscSGS | 0.1 |

**Figure 3 -** *Clustering of the GMPEs of the ARB model into four tectonic groups.*

## Results

Hazard curves were computed in the OQ engine for peak ground acceleration (PGA) and spectral acceleration (SA) at 0.2s, 0.5s, 1.0s, and 2s. The computation was performed on a grid of 38192 sites (spaced at approximately 10 km) with reference soil conditions corresponding to a shear wave velocity in the upper 30 meters (Vs30) of 760-800 m/s.

The hazard map for PGA corresponding to a 10% probability of exceedance in 50 years (475 year return period), can be seen using the interactive viewer. For a more comprehensive set of hazard and risk results, please see the GEM Visualization Tools.

Results from the GEM implementation of the ARB model have been compared against the data provided by Dr. Sokolov from SGS at selected sites (Figure 4). Minor differences have been experienced, mostly interpretable by differences in the software used for the calculation.

**Figure 4 -** *Comparison between results obtained from the GEM implementation of the ARB model and the original SGS results.*

## References

Al-Arifi NS, Fat-Helbary RE, Khalil AR, Lashin AA (2013). A new evaluation of seismic hazard for the northwestern part of Saudi Arabia. Natural Hazards 69, 1435–1457, doi: 10.1007/s11069-013-0756-1

Mohindra R, Nair AKS, Gupta S, Sur U, Sokolov V (2012). Probabilistic seismic hazard analysis for Yemen. International Journal of Geophysics, Article ID 304235. doi:10.1155/2012/304235

Sokolov V, Zahran HM, El-Hadidy SY, El-Hadidy M, Alraddi WW (2017) Seismic hazard assessment for Saudi Arabia using spatially smoothed seismicity and analysis of hazard uncertainty, Bulletin of Earthquake Engineering, 15, 2695–2735, doi: 10.1007/s10518-016-0075-

Zahran HM, Sokolov V, Roobol MJ, Stewart ICF, El-Hadidy SY, El-Hadidy M (2016). On the development of a seismic source zonation model for seismic hazard assessment in western Saudi Arabia, Journal of Seismology 20(3), 747-769, doi: 10.1007/s10950-016-9555-y

Akkar S., Sandikkaya M.A., Bommer J.J. (2014). Empirical ground-motion models for point- and extended-source crustal earthquake scenarios in Europe and the Middle East. Bulletin of Earthquake Engineering, 12(1), 359-387

Atkinson G.M. (2010). Ground motion prediction equations for Hawaii from a referenced empirical approach Bulletin of Seismological Society of America, 100, 751-761, doi: 10.1785/0120090098.

Atkinson GM, Boore DM (2006) Earthquake ground-motion prediction equations for Eastern North America. Bulletin of Seismological Society of America, 96, 2181–2205. doi: 10.1785/0120050245.

Beyer K., Bommer J.J. (2006). Relationships between median values and between aleatory variabilities for different definitions of the horizontal component of motion. Bulletin of Seismological Society of America, 96, 1512–1522, doi: 10.1785/0120050210

Boore D.M., Atkinson G.M. (2008). Ground-motion prediction equations for the average horizontal component of PGA, PGV, and 5%-Damped PSA at spectral periods between 0.01 s and 10.0 s. Earthquake Spectra 24, 99-138

Campbell K.W., Bozorgnia Y. (2008). NGA ground motion model for the geometric mean horizontal component of PGA, PGV, PGD and 5%-damped linear elastic response spectra at periods ranging from 0.1 s to 10.0 s. Earthquake Spectra 24, 139–171, doi: 10.1193/1.2857546.

Munson C.G., Thurber C.H. (1997). Analysis of the attenuation of strong ground motion of the Island of Hawaii. Bulletin of the Seismological Society of America 87, 945–960.

Pankow K.L., Pechmann J.C. (2004). The SEA99 ground-motion predictive relations for extensional tectonic regimes: revisions and a new peak ground velocity relation. Bulletin of the Seismological Society of America 94, 341–348.

Zhao J.X., Zhang J., Asano A., Ohno Y., Oouchi T., Takahashi T., Ogawa H., Irikura K., Thio H.K., Somerville P.G., Fukushima Y. (2006). Attenuation relations of strong ground motion in Japan using site classifications based on predominant period. Bulletin of the Seismological Society of America 96, 898–913.

Gardner J.K., Knopoff L. (1974). Is the sequence of earthquakes in southern California, with aftershocks removed, Poissonian? Bulletin of Seismological Society of America, 64, 1363–1367.

Uhrhammer R. (1986). Characteristics of northern and southern California seismicity. Earthquake Notes 57, p. 21