The Effect Of Dam Impounded Waters On Reservoir Induced Seismicity: Case Studies From Bisri, Qaraoun, And Mseilha Dams

Abstract

The objective of this thesis is to assess the risk of reservoir induced seismicity due to dam impounded water over or near faults, taking into consideration various effects such as the reservoir-fault location, and the amplitude and period of water-level changes. For this purpose, detailed modeling of different case studies was conducted using COMSOL Multiphysics to estimate the destabilization effect of each reservoir on nearby faults. The coulomb failure stresses (CFS) are plotted along the faults, and their variations are observed in relation to pore pressures, normal, and shear stresses. Positive CFS values indicate destabilization of the faults thus a higher probability for seismicity, while negative values indicate stabilization. On one hand, initial seismicity can be seen as an increase in CFS resulting from the initial impoundment of the reservoir as well as diffusion of pore pressure and can prevail for months or few years. On the other hand, protracted seismicity appears after the initial effect of the reservoir filling has diminished and can persist for decades, which presents a serious risk. As such, reservoir induced seismicity is studied for the planned Bisri reservoir and the existing Qaraoun and Mseilha reservoirs, and a comparison among them is made to understand how the location and size of the reservoir with respect to the nearby fault can lead to different results. This thesis aims at providing an understanding of the risks of building dams and impounding water in certain areas without taking into consideration the presence of faults, so that more informed and safe decisions can be made in choosing future dam locations.