شبیه‌سازی تولید، انتشار و بالاروی سونامی در منطقه مکران غربی، قسمت دوم: شبیه‌سازی انتشار و بالاروی

باتوجه به ابهاماتی که در مورد خطرپذیری و پتانسیل خطر وقوع سونامی در سواحل جنوبی ایران وجود دارد، برای درک بهتر خطر سونامی و آمادگی در مقابله با وقوع آن به‌خصوص برای منطقه مکران غربی مدل‌سازی سونامی امری ضروری و لازم می‌باشد. هدف این مطالعه شبیه‌سازی عددی فازهای انتشار امواج سونامی در دریای عمان و شمال اقیانوس هند و بالاروی آن به هنگام رسیدن به سواحل مکران غربی در ایران می‌باشد. در این مطالعه، مدل‌سازی هیدرودینامیکی برای شبیه‌سازی انتشار سونامی در دریای عمان و شمال اقیانوس هند و بالاروی و گسترش سونامی در سواحل جنوب‌شرق ایران مورد استفاده قرار گرفت. در این مطالعه به‌منظور شبیه‌سازی انتشار و بالاروی سونامی از یک شبکه تودرتو استفاده شد. مدل‌سازی بالاروی سونامی در منطقه مکران غربی به‌ترتیب به غرب، میانه و شرق سواحل مکران در ایران تقسیم شد و برای هر منطقه به‌صورت جداگانه مدل‌سازی عددی بالاروی و سیل سونامی انجام شد. چگونگی گسترش و انتشار امواج سونامی، بیشینه ارتفاع موج، بالاروی و سیل امواج و سری زمانی سونامی در نقاطی خاص از جمله نتایج به‌دست آمده از این مطالعه می‌باشند.

Simulation of tsunami generation, propagation and runup in the western Makran, Part 2: Simulation of the propagation and runup

Tsunami numerical modeling is a mathematical description of tsunami life cycle circle including generation, propagation and runup. Numerical simulation is a powerful tool to understand the impacts of past and future events. It is critical to use the results of tsunami simulation such as tsunami waves propagation patterns, time series, amplitudes and runup along coastlines to mitigate tsunami hazard of possible future events. Tsunami waves propagate with a velocity up to 700 to 950 km/h in the ocean without losing a lot of energy. As they reach shallow waters, their amplitude grows larger in the wave shoaling process. Nonlinear shallow water equations are often used to model tsunami wave propagation and runup. The aim of this study is simulation of tsunami wave propagation and runup in the western Makran for a tsunamigenic scenario capable of generating a Mw 8.7 magnitude. The initial condition to of model the tsunami propagation is computed using the Okada's algorithm. The COMCOT hydrodynamic model is used for the numerical tsunami simulation. The COMCOT is capable of solving nonlinear shallow water equations in both Spherical and Cartesian coordinates using explicit staggered leapfrog finite difference schemes and a nested grid configuration. Tsunami propagation is highly influenced by the bathymetry. A three level nested grid system with different resolutions is used for tsunami simulation in this study. Configuring a nested grid system in tsunami modeling is necessary to compute tsunami runup and inundation on dry land. The simulation is then performed for a total run time of 90 minutes with a time step of 0.5 min for the parent grid and 0.0625 min for the finest grid. Numerical modeling of tsunami runup and inundation is performed for the western (C1), central (C2) and eastern (C3) parts of the Makran coastline in the south of Iran. The trapping of tsunami waves inside the Gulf of Oman causes more impacts on the coastlines of Iran and Oman in comparison to the other areas. To investigate the time histories of tsunami waves after the generation by the tsunmigenic scenario, we put 18 virtual gauges near and along the southeastern coastline of Iran. Generally, it takes about 20 minutes for maximum tsunami wave amplitudes to be observed at the southeastern coastlines of Iran. The maximum tsunami wave heights computed for the gauges near Jask and Chabahar are 2/8 and 3/3 m respectively. The entire southeastern coastline of Iran is impacted by such tsunami waves. The maximum computed tsunami wave height along the southeastern coastline of Iran is 11m. The maximum tsunami wave field exhibits a significant local hazard field inside the Gulf of Oman posed to the shores of Iran and Oman. The maximum tsunami amplitude reaches up to 11 m and 6 m inside the Gulf of Oman the Arabian Sea Basins, respectively. The results of runup modeling show that the maximum computed runup for the C1, C2 and C3 areas are 10, 17 and 19 m. The maximum tsunami inundation distance for those areas are 6, 6 and 4 km, respectively. The considerable values of inundation distance are due to low elevation topography of the affected coasts. Computing the tsunami inundation distance can be used in choosing evacuation lines during the possible future tsunamis and finding safer locations along the coastal areas. Accurate tsunami simulations are required to develop a tsunami early warning system and estimate the tsunami inundation on dry land. To perform more accurate simulations, high resolution local bathymetric/topographic maps are required, especially for the major ports in southeastern Iran.