Introduction: Why Beirut?

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Beirut, the capital of Lebanon with a population of 2.4M approximately, is exposed to a high seismic hazard due to its location which is close to major faults:

* Mount Lebanon Fault

* Yammouneh Fault

* Roum Fault

* Rachaya and Serghaya Fault

The earthquakes produced previously from these faults had an estimated magnitude up to 7.6, which resulted in drastic damages.

The variability of the geology in Beirut leads to a high variability in the seismic site response over the city. Strong amplification has been observed on the quaternary deposits (sand dunes or alluvial sediments) compared to the rocky outcrop at ECPT.

The liquefaction potential in Beirut is significant. According to Sadek et al. (2004), the factor of safety against liquefaction at 5-m depth is less than 1 in a large portion of Western and Southwester suburbs of Beirut.

<figure><img src="image_3.png" /><figcaption>Liquefaction potential at 5-m depth according to Sadek et al. (2004)</figcaption></figure>

<caption>Water table depth observed in Beirut from the boreholes database</caption>

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Introduction: Why Beirut?

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The estimation of the local hazard requires the analysis of a large number of data, in particular geotechnical data in order to be able to both determine the seismic response of the sites and their liquefaction potential.

576 boreholes have been collected in the Beirut area (dark blue). Moreover, 751 (light blue) geophysical H/V measurements were already done.

A statistical study of the variability of the mechanical parameters in the soil layers resulting from these boreholes will be carried out in order to deduce the lengths of correlation (horizontal and vertical) characterizing these parameters and making it possible to study the effect of these heterogeneities on the seismic movement produced at the surface.

* Boreholes collected are spread along different geological layers.

* Each soil report refers to a different geotechnical laboratory with a different way to visualize the lithostratigraphy

BH-log with detailed parameters

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Building Dataset

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Two different representations of same boreholes dataset for:
* Geological Modelling
* Numerical Simulations

Reference - Acknowledgments

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Charles Scolik 1894 Austrian photographer

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Brax et al 2019 An Earthquake Catalog for the Lebanese Region

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Brax et al 2018 Towards a microzonation of the Greater Beirut area: an instrumental approach combining earthquake and ambient vibration recordings

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Sadek et al 2004 A GIS-based framework for the evaluation of seismic geo-hazards in the greater Beirut area

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Dubertret 1944 Geological Map of Beirut

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RUMMARE (2013-2019) : Research Unit associated to CNRS-L on Mass movements Hazards Assessment and Risk Evaluation)

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Private Geotechnical Laboratories (SANA group – Phi Prime Engineering - Dar Al Handasa - GGE company- Geostruc

Data Collection

The estimation of the local hazard requires the analysis of a large number of data, in particular geotechnical data in order to be able to both determine the seismic response of the sites and their liquefaction potential.

576 boreholes have been collected in the Beirut area (dark blue). Moreover, 751 (light blue) geophysical H/V measurements were already done.

A statistical study of the variability of the mechanical parameters in the soil layers resulting from these boreholes will be carried out in order to deduce the lengths of correlation (horizontal and vertical) characterizing these parameters and making it possible to study the effect of these heterogeneities on the seismic movement produced at the surface.

BH-log with no detailed parameters

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230 boreholes exist in the “Quaternary red soil without pebbles-G14”.

Two examples of different visualization of stratigraphy in G14

Building 3D Model

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G9

Fill

Silty Sand

Clay medium plasticity

Limestone with chert with some marl content

Clay high plasticity

Sandy clay with limestone cobbles

Weathered limestone marlstone

Limestone and Marlstone

Startigraphy

Geological Layers

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G1: CRETACEOUS Gres de Nubie siliceux

G2: CRETACEOUS Aptien argillo-sableux calcaire inférieur

G3: CRETACEOUS Aptien argillo-sableux calcaire supérieur

G4: CRETACEOUS Albien marnes vertes, calcaires

G5: CRETACEOUS Cenomanien calcaire dolomitique

G6: CRETACEOUS Senonian marne blanche

G7: TERTIARY Miocene calcaire marneux

G8: TERTIARY Miocene, poudingues breches

G9: QUATERNARY Terre brune a cailleux calcaires

G10: QUATERNARY Terre ocre, sableux

G11: QUATERNARY Alluvions, eboulis, apports recent

G12: QUATERNARY Gres d'uneure(ramleh); poudingues

G13: QUATERNARY Terre rouge sableux

G14: QUATERNARY Terre rouge sableux sans galets

G15: QUATERNARY Dune mouvante

Geophysical H/V [751]

Geological Layers

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G1: CRETACEOUS Gres de Nubie siliceux

G2: CRETACEOUS Aptien argillo-sableux calcaire inférieur

G3: CRETACEOUS Aptien argillo-sableux calcaire supérieur

G4: CRETACEOUS Albien marnes vertes, calcaires

G5: CRETACEOUS Cenomanien calcaire dolomitique

G6: CRETACEOUS Senonian marne blanche

G7: TERTIARY Miocene calcaire marneux

G8: TERTIARY Miocene, poudingues breches

G9: QUATERNARY Terre brune a cailleux calcaires

G10: QUATERNARY Terre ocre, sableux

G11: QUATERNARY Alluvions, eboulis, apports recent

G12: QUATERNARY Gres d'uneure(ramleh); poudingues

G13: QUATERNARY Terre rouge sableux

G14: QUATERNARY Terre rouge sableux sans galets

G15: QUATERNARY Dune mouvante

Geotechnical and Geophysical data collected

Working on the homogenization of each geological layer

was done following the steps:

* Reading each soil report

* Localizing each BH on google earth

* Reading the stratigraphy of each BH and reaching a homogenized column where each layer of this column should be found in the BH of the same geological layer

* Building the dataset on excel

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