Earthquake Hazard in Lebanon

The following sections are included:

• About the Authors

• Acknowledgements

• Table of Contents

The following sections are included:

• Non-Specialist

• Specialist

On a public awareness level, seismic hazard and risk in Lebanon is not well-known. This is mainly due to the long return period of earthquakes in this region, with infrequent but seriously damaging earthquakes. The region is currently undergoing total transformation, as a consequence of the relative political stability that Lebanon has enjoyed recently after years of political and social strife. A most ambitious building programme is underway, funded by internal and external sources. In such situations, it is often the case that considerations of medium term hazard from natural disasters are ignored in favour for economic development and rapid construction. It is clear that Lebanon, whilst experiencing an economic uprising, the fabric of the economy and indeed society is still fragile. An increased awareness of the hazard from natural disasters, especially earthquakes, is therefore of great significance, in order that the case for a more considered approach towards design and construction of new facilities and structures is stressed. It is mainly to raise awareness as well as provide the best available technical data on earthquake risk that these series of studies have been initiated. This book is Phase I of a multi-phase programme covering the following…

The following sections are included:

• Active Tectonics of the Levant and Dead Sea Fault Zone

• Historical Seismicity

• Estimates of Rates

• Twentieth Century Seismicity of the Levant and Lebanon

Lebanon occupies a small area comprised between 33° and 34°N and 35° to 36°E and seismic activity there during the 20th century has been very low. During the 20th century there have been 60 earthquakes in this area but only 13 of them reached a magnitude Ms ≥ 4.0, Table 4.1. The total amount of seismic moment release in the last 100 years is trivial and only 1.3 × 10²⁵ d.cm, which is equivalent to a single earthquake of about M_s = 5.8…

Historical seismicity shows that large earthquakes have occurred in the past in the Lebanese section of the Dead Sea fault zone. It is probable that at least two of these, in 1202 and 1759, occurred on the straight Yammouneh fault segment of the main left-lateral fault system itself (Ambraseys and Melville 1988; Ambraseys and Barazangi 1989), which runs NNE-SSW for about 150~km and is thus oblique to the overall Africa-Arabia motion. It is therefore not surprising that in this area the deformation is probably distributed over more than one fault, and may even be separated into its strike-slip and thrust components, as is seen elsewhere in regions of oblique convergence such as central California (e.g. Mount and Suppe 1987). A manifestation of this distributed deformation may be the large (M ~ 7) earthquake of 1837 in southern Lebanon, which appears not to have occurred on the Yammouneh fault, and may have been on the Roum fault instead (see Section 3.2 and Ambraseys, 1997)…

The following sections are included:

• Peak Ground Acceleration (PGA)

• Peak Ground Displacements (PGD)

• Acceleration Response Spectra (SA)

• Displacement Response Spectra (SD)

The following sections are included:

• Completeness Test

• Source Zone Modelling

• Dead Sea Rift Zone

• East Anatolian Fault Zone

• Yammouneh Fault Zone

• Maximum Magnitudes

The following sections are included:

• Peak Ground Accelerations (PGA)

• Peak Ground Displacements (PGD)

• Spectral Accelerations (SA) and Spectral Displacements (SD)

The following sections are included:

• City of Beirut

• City of Tripoli

• City of Sidon

Probabilistic seismic hazard assessment (PSHA) has become the most widely used approach to estimating the levels of earthquake actions to be considered in design. PSHA offers many advantages to the analyst, amongst which is the important feature of being able to assign return periods to different levels of ground motion – as has been done in this study – which provides a very convenient tool for selecting design motions for different performance levels and different importance categories of structures. Furthermore, PSHA allows all of the uncertainties associated with seismic hazard assessment to be taken into account, particularly those associated with size and location of future earthquakes. In addition to these features, normal PSHA procedures allow the effects of all the potential earthquakes that could affect a site to be amalgamated into a single expression of the hazard either as peak ground-motion parameters or response spectral ordinates…

Please refer to full text.

The following sections are included:

• Appendix A1: Surface Wave Magnitude

• Appendix A2: Application of Stepp Method

• Appendix A3: Hazard Maps for Lebanon and Vicinity

• References