THE POTENTIAL OF TSUNAMI GENERATION ALONG THE MAKRAN SUBDUCTION ZONE IN THE NORTHERN ARABIAN SEA. CASE STUDY: THE EARTHQUAKE AND TSUNAMI OF NOVEMBER 28, 1945

THE POTENTIAL OF TSUNAMI GENERATION ALONG THE MAKRAN SUBDUCTION ZONE IN THE NORTHERN ARABIAN SEA. CASE STUDY: THE EARTHQUAKE AND TSUNAMI OF NOVEMBER 28, 1945 George Pararas-Carayannis Honolulu, Hawaii, USA ABSTRACT Although large earthquakes along the Makran Subduction Zone are infrequent, the potential for the generation of destructive tsunamis in the Northern Arabian Sea cannot be overlooked. It is quite possible that historical tsunamis in this region have not been properly reported or documented. Such past tsunamis must have affected Southern Pakistan, India, Iran, Oman, the Maldives and other countries bordering the Indian Ocean. The best known of the historical tsunamis in the region is the one generated by the great earthquake of November 28, 1945 off Pakistan's Makran Coast (Balochistan) in the Northern Arabian Sea. The destructive tsunami killed more than 4,000 people in Southern Pakistan but also caused great loss of life and devastation along the coasts of Western India, Iran, Oman and possibly elsewhere. The seismotectonics of the Makran subduction zone, historical earthquakes in the region, the recent earthquake of October 8, 2005 in Northern Pakistan, and the great tsunamigenic earthquakes of December 26, 2004 and March 28, 2005, are indicative of the active tectonic collision process that is taking place along the entire southern and southeastern boundary of the Eurasian plate as it collides with the Indian plate and adjacent microplates. Tectonic stress transference to other, stress loaded tectonic regions could trigger tsunamigenic earthquakes in the Northern Arabian Sea in the future. The northward movement and subduction of the Oman oceanic lithosphere beneath the Iranian micro-plate at a very shallow angle and at the high rate is responsible for active orogenesis and uplift that has created a belt of highly folded and densely faulted coastal mountain ridges along the coastal region of Makran, in both the Balochistan and Sindh provinces. The same tectonic collision process has created offshore thrust faults. As in the past, large destructive tsunamigenic earthquakes can occur along major faults in the east Makran region, near Karachi, as well as along the western end of the subduction zone. In fact, recent seismic activity indicates that a large earthquake is possible in the region west of the 1945 event. Such an earthquake can be expected to generate a destructive tsunami. Additionally, the on-going subduction of the two micro-plates has dragged tertiary marine sediments into an accretionary prism - thus forming the Makran coastal region, Thick sediments, that have accumulated along the deltaic coastlines from the erosion of the Himalayas, particularly along the eastern Sindh region near the Indus River delta, have the potential to fail and cause large underwater tsunamigenic slides. Even smaller magnitude earthquakes could trigger such underwater landslides. Finally, an earthquake similar to that of 1945 in the Makran zone of subduction, has the potential of generating a bookshelf type of failure within the compacted sediments – as that associated with the “silent” and slow 1992 Nicaragua earthquake – thus contributing to a more destructive tsunami. In conclusion, the Makran subduction zone has a relatively high potential for large tsunamigenic earthquakes. Science of Tsunami Hazards, Vol. 24, No. 5, page 358 (2006) INTRODUCTION Large earthquakes along the Makran Subduction Zone (MSZ) have generated destructive tsunamis in the past (Berninghausen, 1966). Although the historic record is incomplete, it is believed that tsunamis from this region had significant impact on several countries bordering the Northern Arabian Sea and the Indian Ocean. The tsunami generated along the MSZ on November 28, 1945 was responsible for great loss of life and destruction along the coasts of Pakistan, Iran, India and Oman (Qureshi, 2006; Pakistan Meteorological Department 2005; Mokhtari and Farahbod, 2005; PararasCarayannis, 2006a). The effects of this tsunami on other countries bordering the Indian Ocean have not been adequately documented. Reports on the potential for tsunami generation along the Makran coast of Pakistan have been cursory. Based on a thorough review of recent geophysical surveys and seismic data, the present study analyzes the potential tsunami generation mechanisms along the MSZ by reviewing subduction processes of the Oman oceanic lithosphere underneath the Iranian microplate and - more specifically the seismotectonics of the east and west segments, including the section in the Gulf of Oman. Furthermore, the study examines the seismo-dynamics of compressional collision of the India and Eurasia plates along the northwestern boundary of India in the vicinity of the Northern Arabian Sea as potential sources of future tsunamis and evaluates the tsunami risk from major earthquakes along coastal Karach, the deltaic Indus region and the grabens of Northwestern India. Finally, the study evaluates the possible effects of the extensive sedimentation from major rivers in the region on subduction processes. THE TSUNAMI OF 28 NOVEMBER 1954 ALONG THE MAKRAN COAST OF PAKISTAN IN THE NORTHERN ARABIAN SEA On November 28, 1945, an earthquake, off Pakistan's Makran Coast (Balochistan) generated a destructive tsunami in the Northern Arabian Sea and the Indian Ocean. More than 4,000 people were killed in Pakistan by both the combined effects of the earthquake and the tsunami. However, the tsunami was responsible for most of the loss of life and the great destruction, which occurred along the coasts of Iran, Oman and northwestern India (Pararas-Carayannis, 2006b). THE EARTHQUAKE The great earthquake occurred at 21:56 UTC (03:26 IST), on 28 November 1945). Its epicenter was off the Makran coast at 24.5 N 63.0 E (24.2 N, 62.6 E according to USGS, in the northern Arabian Sea, about 100 km south of Karachi and about 87 kms SSW of Churi (Baluchistan), Pakistan. The quake’s focal depth was 25 kms. The earthquake's Richter Magnitude (Ms) was 7.8. The Moment Magnitude (Mw) was later given as 7.9 and reevaluated to be 8.1 (Pacheco and L. Sykes, 1992). The quake was recorded by observatories in New Delhi, Kolkata (Calcutta) and Kodaikanal. Its intensity was high throughout the region. It was strongly felt in Baluchistan and the Las Bela area of Pakistan. It was reported that in the western and southern sections of Karachi the strong surface motions lasted for about 30 seconds. Science of Tsunami Hazards, Vol. 24, No. 4, page 359 (2006) According to eyewitness reports, people were "thrown out of their beds", doors and windows rattled, and windowpanes broke. The underwater cable link between Karachi and Muscat (Oman) was damaged, disrupting communications. The lighthouse at Cape Moze - 45 miles from Karachi - was also damaged. The earthquake was strongly felt also at Manora, where the lighthouse was damaged. It was moderately felt in Panjgaur and Kanpur. Other Earthquake Eff (...truncated)