Probabilistic Tsunami Hazard Analysis of the Makran Region
Abstract
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.