كليدواژه :
مكران و سونامي , جنوب‌شرق ايران , تحليل خطر احتمالاتي , مدل‌سازي عددي
چكيده فارسي :
علي‌رغم ابهام در رفتار لرزه‌زايي زون فرورانش مكران در ساحل جنوب‌شرق ايران كه به‌دليل لرزه‌خيزي كم آن است، شواهد تاريخي و سونامي سال 1945 ميلادي، بيان‌كننده پتانسيل سونامي‌زايي اين زون هستند. رخداد سونامي‌هاي محتمل در آينده، ايران را بيش از هر كشور ديگري در معرض خطر ناشي از آن قرار خواهد داد. تحليل خطر احتمالاتي سونامي، راهي موثر براي ارزيابي خطر ناشي از سونامي‌ها و كمكي جهت برنامه‌ريزي براي آينده است. در اين مطالعه، با درنظرگرفتن زون فرورانش مكران، مكران غربي و مكران شرقي به‌عنوان چشمه‌هاي توليدكننده سونامي، به برآورد خطر احتمالي سونامي در ساحل جنوب‌شرق ايران پرداخته شد. سناريوهايي براي وقوع زمين‌لرزه‌هايي با بزرگاي بين 5/7 تا 9/8 براي مكران غربي و مكران شرقي و سناريوهايي با بزرگاي بين 5/7 تا 1/9 براي كل مكران درنظرگرفته‌شد. در اين تحقيق، از نتايج مدل‌سازي عددي سونامي براي تحليل خطر احتمالاتي سونامي استفاده شد. نتايج، ساحل كنارك (واقع در استان سيستان و بلوچستان، جنوب‌شرق ايران) را خطرپذيرترين ناحيه ساحلي در ميان نقاط مهم مختلف براي سناريوهاي مورد مطالعه نشان داد. كمترين خطرپذيري نيز از آن سيريك (واقع در استان هرمزگان، جنوب ايران) است. نتايج، حاكي از لزوم توجه به خطر درازمدت سونامي در اين منطقه مهم از كشور ايران، به‌خصوص ناحيه بين جاسك و بريس است.
چكيده لاتين :
Despite the ambiguous tsunamigenic behavior of the Makran Subduction Zone (MSZ), due to the low level of
offshore seismicity, historical evidences and the 1945 tsunami in Makran confirm the potential of the MSZ for
generating tsunami events. Possible future tsunamis generated by the MSZ will pose the coastlines of Iran to
hazard more than any other country. Probabilistic tsunami hazard assessment (PTHA) is an effective approach to
assess hazard from tsunamis and help for planning for the future. In this study, we assess the probabilistic
tsunami hazard along the southeastern coast of Iran considering the entire Makran, the western Makran and the
eastern Makran tsunamigenic sources.
Tsunami scenarios include earthquakes of magnitudes between 7.5-8.9 for the western and eastern Makran
and between 7.5-9.1 for the entire Makran. Both seismicity and tsunami numerical simulation are inputs for
probabilistic hazard analysis. Assuming that the tsunami sources are capable of generating tsunamigenic
earthquakes, estimating the annual rate of these events is required for PTHA. The truncated Gutenberg-Richter
relation (Cosentino et al., 1977 and Weichert, 1980) is used in this study to compute the annual number of the
earthquakes. We model tsunamis using the COMCOT well-known algorithm (Liu et al., 1998). The distributions
of tsunami heights along the coastline of Iran are used in probabilistic tsunami hazard assessment.
The results of PTHA show that Konarak and Sirik coastlines are posed to the most and least hazard from
tsunamis, respectively. The probability of exceeding (POE) 1 and 3 meters increases with time. The probability
that tsunami wave height exceeds 3 meters in 500 years is about 0.63 and 0 near the coastlines of Konarak and
Sirik, respectively. The maximum POE for 3 meters belongs to the area between Beris and the west of Kereti.
Distributions of probabilistic tsunami height along the coastline of Iran also indicate that Konarak and Sirik are
the most and least vulnerable shorelines to tsunami hazard, respectively. The annual probability of exceeding 1, 2
and 3 meters are 1, 0.4 and 0.2, respectively. The results indicate the need of attention to tsunami long-term
hazard along the southeastern coast of Iran, especially for the area between Jask and Beris.
Our tsunami hazard assessment does not involve the tsunami inundation distances on dry land due to lack of
high resolution site-specific bathymetric/topographic maps. Such computations are required in order to estimate
the exact impacts of possible future tsunamis on the southeastern coast of Iran. High-resolution hydrographic
surveys are required to be done in future for the major ports. Furthermore, future works should consider other
possible near-field tsunami sources, such as the Murray Ridge, Minab-Zendan and Sonne faults and far-field
tsunami sources, such as the Sumatra-Andaman subduction zone.
