Doctor of Philosophy
The Makran Subduction Zone (MSZ) in the northwestern Indian Ocean can generate large thrust earthquakes that could trigger significant tsunamis. The coastal regions of Pakistan, Iran, Oman, and western India are prone to tsunami hazards due to the occurrence of earthquakes in the MSZ. This thesis carries out a thorough assessment of the tsunami hazard of the MSZ in three main steps, each presented in a separate chapter. In the first chapter, the tsunami hazard of the 1945 MSZ event is assessed using stochastic earthquake rupture models of moment magnitude (Mw) of 8.1–8.3. In the second chapter, the effects of possible rupture of splay faults on the tsunami hazards are studied by developing a framework that uses a logic tree and stochastic earthquake rupture models by considering eastern MSZ as a case study. In the third chapter, probabilistic tsunami hazard analysis is conducted for the MSZ using stochastic tsunami simulations for Mw 7.7–9.1 earthquake scenarios combined with a logic tree method. This thesis considers uncertainties related to rupture geometry and location, slip heterogeneity, seismic moment split ratio, earthquake slip asperity location within a fault plane, earthquake occurrence rate, single-segment (eastern and western MSZ) or two-segment (full MSZ) rupture scenarios. To quantify these uncertainties, a total number of 19,484 tsunami source models are simulated, systematically. The results identify the stochastic source models that matches the existing observations of the 1945 Makran event. Also, they show significant local amplification of the maximum tsunami heights due to splay faults. The tsunami heights are highly sensitive to the characteristics of the source model, such as the location of the large slip areas, the bathymetry of the nearshore area, and the location of bays along the coastline. The tsunami hazard in the central parts of the shoreline is more significant than at the eastern and western boundaries. Moreover, the tsunami hazard along the western MSZ coastline, i.e., the Iranian portion, is greater than that along the eastern part. Consideration of different occurrence rates results in significant variability in the estimated 475, 975, and 2475-year tsunami heights for the MSZ shoreline.
Summary for Lay Audience
Historical records of major earthquakes in the northwestern Indian Ocean along the Makran Subduction Zone (MSZ) indicate high potential tsunami hazards for coastal regions of Pakistan, Iran, Oman, and western India. There are fast-growing and populous cities and ports that are economically important, such as Chabahar (Iran), Gwadar (Pakistan), Muscat (Oman), and Mumbai (India). The MSZ might be seismically segmented into eastern and western parts. In terms of seismicity, eastern MSZ is more active during the past two hundred years. However, based on the recent findings, western MSZ might be locked and accumulating elastic strain. In other words, western MSZ might be able to produce large tsunamigenic earthquakes. In the case of full rupture of the MSZ, it can generate up to moment magnitude (Mw) of 9.1 megathrust earthquakes which is similar to the catastrophic 2004 Sumatra and 2011 Tohoku earthquakes and tsunamis. Compared to other subduction zones around the world, the MSZ is relatively understudied. This thesis is an effort to fill this research gap by using stochastic earthquake rupture models and a logic tree to study the tsunami hazard posed by the MSZ. The incorporated uncertainties are generally associated with the earthquake source parameters, such as fault geometry, slip heterogeneity, and seismicity of the region. This research is conducted in three main steps. Firstly, the most recent recorded tsunami in the region, which occurred in 1945, is examined carefully. The magnitude range for this event was estimated to be from 8.1 to 8.3. Secondly, the effect of splay faults on tsunami hazard is examined. Thirdly, a full probabilistic tsunami hazard assessment of the MSZ region is performed by considering a wide range of possible earthquake scenarios. The results of this study show the significant impact of considered uncertainties on tsunami hazards and indicate the need for thorough paleotsunami studies and more accurate bathymetry data for the region.
Momeni, Payam, "Probabilistic Tsunami Hazard Analysis of the Makran Region" (2023). Electronic Thesis and Dissertation Repository. 9743.
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