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This level is defined as the largest ground motion that can reasonably be expected at the site from a nearby seismic source or on the basis of the seismic history and tectonics of the region. The DSHA is considered the most appropriate approach to estimate ground motion levels for this scenario. The dam and appurtenant structures may sustain irreparable damage but the uncontrolled release of reservoir water must be prevented. In this study Return Period of occurring of the MCE is more than 2000 years. For Gambiri diversion dam site, return periods of 200, 500 and 2500 years were considered for the OBL, DBL and MDL respectively and using the 84th percentile of the distribution. 3.4. PROBABILISTIC SEISMIC HAZARD ANALYSIS (PSHA) PSHA allows the use of multi-valued or continuous events and models to arrive at the required description of the earthquake hazard. Ground motion levels are expressed in terms of probabilistic estimates such as the probability of occurrence of the PGA for a given period of time. The method also allows quantifying the uncertainty of the ground motion parameters. Two models were considered, the seismic point source model and the seismic line source model. 3.4.1. Seismic Point Source (or Poisson) Model This is the oldest approach employing probabilistic tools. The earthquakes are modeled as point sources considering magnitude, epicenter and focal depth. Events are considered independent of each other. The use of this model is advantageous for situations where the identification of faults in an area is difficult and where large and frequent earthquakes have occurred near the site. However, the method cannot consider uncertainties in magnitude and epicentral distance nor does it accept historical earthquakes in the calculations. Since there are numerous large historical earthquakes around the Gambiri diversion dam site, results obtained by this model are believed not to be reliable and they are used for reference purpose only. Calculations were performed using the Gumbel type I distribution function [9]. 3.4.2. Seismic Line Source Model This model better fits the many line sources (faults). It can be treated by the well-known software SEISRISK III [10]. Input parameters required include: geometry and location of each seismic source (fault, source zones, including uncertainty), attenuation relationships, and seismicity parameters β and λ (used in the 5 distribution function of the doubly truncated Gutenberg-Richter equation 1104