PhD Thesis

Figure: Displacement wavefield snapshot of simulation 4,6 and 10 seconds after source injection.

Abstract: Tehran, the capital of Iran, is situated in the southern part of the central Alborz, a region of very high seismicity due to several large active faults. Moreover, the city is built on thick alluvial deposits from the Alborz Mountain Range, which can significantly amplify seismic waves, thus dramatically increasing their impact on Tehran's building stock. Under these conditions, it is crucial to accurately define the geometry and properties of Tehran's alluvial basin to predict more realistic surface ground motion for future earthquakes.
Past seismological studies have revealed significant amplification of seismic ground motion across a broad frequency range (from 0.4 Hz to 4 Hz), yet detailed knowledge of Tehran’s basin geometry and properties for use in seismic strong ground motion simulations is still lacking. Two phenomena have been suggested to explain the observed amplification: the first is the existence of very thick sedimentary layers with a gradual increase in shear wave velocity, accounting for amplification at low frequencies (0.4 Hz), and the second is site effects caused by the deep sedimentary basin, leading to amplification over a wide range of frequencies.
To address the origin of this amplification, we constructed the first experimental 3D model of the Tehran basin.
The final results based on strong ground motion simulations can underscore the importance of local site effects for the first time in the context of Tehran's seismic hazard assessment.
The full version of thesis can be found at: https://theses.fr/2023GRALU032

This thesis is conducted within the framework of Franco-Iranian cooperation on the seismic risk of Tehran, involving ISTERRE and IIEES, under the TRIGGER-GDRI CNRS program.