| Abstract Submission No. | ABS-3.1-0231 |
| Title of Abstract | Past Tsunamis in the Arabian Sea and Future Possibilities |
| Authors | Dr. B.K. Rastogi* |
| Organisation | President, Ind. Soc. Earthq. Sc. |
| Address | NA NA, NA, India Pincode: NA E-mail: bkrastogi12@gmail.com |
| Country | India |
| Presentation | Oral |
| Abstract | Future source zones of earthquakes that can generate tsunamis in the Indian Ocean are identified based on past seismicity and gap areas. The tectonics and seismicity in these zones are briefly discussed and long-term assessment of future tsunamigenic great / major / moderate earthquakes in these zones is presented. The two subduction zones which can give rise to great earthquakes are Sunda Arc (Sumatra and Java) and Makran coast. The Sunda Arc generates frequent great earthquakes, volcanoes and tsunamis. The Andaman-Nicobar group of islands is also seismically active zone that generates frequent earthquakes. However, northern Sumatra and Andaman-Nicobar regions are assessed to be probably free from great earthquakes for a several decades due to occurrence of 2004 Mw 9.3 and 2005 Mw 8.7 earthquakes. The M8 earthquakes in the southern Sumatra and Java can generate strong tsunamis, however, the directivity will not be towards India. Only in rare case of mega earthquake or mega volcanic eruption, the tsunami could be hazardous for India. For example, the Krakatoa volcano along the Sunda arc between Java and Sumatra caused one of the most catastrophic explosive eruptions in 1883 and largest tsunami in history. Thrust-type earthquakes along the 1200-km-long Makran subduction zone of Iran-Pakistan situated on the northwestern side of the Arabian Sea can generate tsunamis. It had at least five great earthquakes of M 8+ along different ~200-km long rupture zones which generated tsunamis and mud volcanoes in the past: 1483 (Long. 58° - 60°E), 1851 and also 1864 near Gwadar (Long. 61° - 63°E), 1945 (Long. 63° - 65°E) and 1765 (Long. 65° - 67°E) in easternmost Makran. The 28 Nov. 1945 (Mw 8.0) earthquake generated the last major tsunami in the Arabian Sea. More than 4000 people were killed on the Makran coast by both the earthquake and the tsunami. This earthquake occurred in the central part of the Makran zone. Eastern and western parts remain potential zones for great earthquakes. It is also possible that the entire length of Makran subduction zone ruptures in one go in M9+ mega earthquake accompanied by landslide generating mega tsunami like that of 2004 Sumatra-Andaman. It is estimated that waves height could reach ~5 m along the Indian coast and 11 m in Gulf of Kachchh for a tsunami due to M8+ earthquake and much higher for a mega earthquake along the Makran coast. Thrust-type major earthquakes occurring along coastal zones of compressive stress along the Indus delta and Kutch-Saurashtra region have given rise and can again generate moderate tsunamis. Minor tsunamis can be generated due to dip-slip earthquakes along oceanic ridges. A local tsunami with maximum amplitude of 1.5 m was generated due to normal faulting earthquake of Mw 7.7 on November 30, 1983 at Diego Garcia Archipelago. |
| Keywords | Arabian Sea, Sumatra and Java, Makran coast |