Tsunami, Earthquakes, Hurricanes, Volcanic Eruptions and other Natural and Man-Made Hazards and Disasters - by Dr. George Pararas Carayannis

Tsunami, Earthquakes, Hurricanes, Volcanic Eruptions and other Natural and Man-Made Hazards and Disasters

Tsunamis of the Indian Ocean

George Pararas-Carayannis

Copyright © 2005. All Rights Reserved

Introduction

Although not as frequent as in the Pacific Ocean, tsunamis generated in the Indian Ocean pose a great threat to all the countries of the region. The most vulnerable are: Indonesia, Thailand, India, Shri Lanka, Pakistan, Iran, Malaysia, Myanmar, Maldives, Somalia, Bangladesh, Kenya, Madagaskar, Mauritius, Oman, Reunion Island (France), Seychelles, South Africa, and Australia.

The Great Earthquake of December 26, 2004 off the west coast of Northern Sumatra generated the most devastating tsunami in history. It killed more than 225,000 people with thousands more reported missing and left unprecedented devastation along its path across the Bay of Bengal and the entire Indian Ocean.

Although not as destructive as the 26 December 2004 event was, many more tsunamis have been generated by large earthquakes in subduction zones bordering the Indian Ocean and by smaller magnitude events along the Central Indian and Carlsberg mid-oceanic ridges. The recent historical record shows that major tsunamis occurred in 1524, 1762, 1819, 1847, 1881, 1941, 1945, 1977 and in 2004. Additionally, the 26 August 1883 Ultra Plinian eruption and collapse of the Krakatau (Krakatoa) volcano in the Sunda Strait - between Java and Sumatra - generated the best known and documented tsunami in recorded history. This particular tsunami killed 37,000 people in the islands of Java and Sumatra. There may be additional destructive tsunamis in the Indian Ocean that have not been properly documented. For example villagers of Simeulue Island , off the coast of Sumatra, speak of a destructive tsunami in 1907 that had killed thousands of people.

Seismotectonics of the Indian Ocean Region - Potential Tsunami Generating Sources

The following is only a brief overview of the tectonic setting and interactions that result in tsunamigenic earthquakes in the Indian Ocean.

The India tectonic plate has been drifting and moving in a north/northeast direction, for millions of years colliding with the Eurasian tectonic plate and forming the Himalayan mountains.

USGS graphic showing the migration of the Indian tectonic plate

As a result of such migration and collision with both the Australian and the Eurasian tectonic plates and subplates, the Indian plate's eastern boundary is a diffuse zone of seismicity and deformation, characterized by extensive faulting and numerous earthquakes that can generate destructive tsunamis.

To the west, similar interaction of the India plate with the Arabian and Iranian microplates of the Eurasian block, has created an active subduction zone along the Makran coast of Pakistan. A major fault in this region has produced several tsunamigenic earthquakes recently and in the distant geologic past. This major fault is of the same character as the West Coast fault along the coast of Maharashtra, India - which is also a region that can produce tsunamigenic earthquakes. Further south on the western side the Indian tectonic plate is bounded by the Central Indian and Carlsberg mid-ocean ridges, a region of shallow seismicity.

To the east, subduction of the Indo-Australian Plates beneath the Burma and Sunda Plates has formed the extensive Sunda Trench - a very active sismic region where large earthquakes are frequent. The volcanoes of Krakatau, Tambora and Toba , well known for their violent eruptions, are byproducts of such tectonic interactions. A divergent boundary separates the Burma plate from the Sunda plate in the north. The Burma plate encompasses the northwest portion of the island of Sumatra as well as the Andaman and the Nicobar Islands, which separate the Andaman Sea from the Indian Ocean.


Destructive tsunamis can originate from earthquakes that occur along these principal tectonic sources . The major tectonic feature in the region is the Sunda Arc that extends approximately 5,600 km between the Andaman Islands in the northwest and the Banda Arc in the east. The Sunda Arc consists of three primary segments; the Sumatra segment, the Sunda Strait Segment and the Java Segment. These locations represent the area of greatest seismic exposure, with maximum earthquake magnitudes of up to 7.75 or even more on the Richter scale - as the 26 December 2004 proved.

According to recent studies reported in the Earth and Planetary Science Letters (vol 133), the Indo-Australian plate does not appear to be coherent. The two plates appear to have separated many million years ago. Also, it appears that the Australian plate is rotating in a counterclockwise direction, putting stress on the southern segment of the India plate.

The movement of the Australian plate can generate earthquakes along the southern end of western Sumatra, along the Sunda Strait segment of the great tectonic arc, or further east along the Java segment, off the Lesser Sunda Islands or at Flores Island of Indonesia. Active tectonic interaction in this eastern section of the great arc has produced destructive earthquakes and tsunamis in the distant past and as recently as 1977, 1992 and 1994.

Smaller magnitude earthquakes along the mid-Indian ocean ridge have the potential of generating smaller local tsunamis. Finally, deltaic sediment accumulations of major rivers have also the potential of generating tsunamis. Such landslides can be triggered even by earthquakes of lesser magnitude.

British Geological Survey graphic of the seismicity of Southern Asia of the Carlsberg Midoceanic Ridge and of the southern portion of the Arabian Peninsula and the Red Sea.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Recent Tsunamis of the Indian Ocean

(partial listing - being updated)

Although not as frequent as in the Pacifc, destructive earthquakes and tsunamis have occurred in the Indian Ocean troughout geologic history and in recent times. Most of these events have not been adequately documented, leading to the erroneous impression by many that tsunamis do not occur often enough to present a risk that requires the establishment of a Regional Tsunami Warning System in the Indian Ocean.

However, the destruction and high death toll caused by the 26 December 2004 tsunami disaster indicates how underestimated this hazard has been - especially by the countries that were so adversely afflicted. Although not frequent , major tsunamis have occurred in the Indian Ocean. At least eight of these were major events, which have been documented - but some not adequtely . Of course, one of these was the well-known catastrophic tsunami generated from the ultra Plinian eruption of Krakatau on 26 August, 1883. The tsunami waves reached over 30 meters and killed about 37,000 people in Java and Sumatra.

Other major tsunamis occurred in 1524, 1762, 1819, 1847, 1881, 1941, 1945 and in 1977. Less destructive tsunamis have also occurred more recently. The following is a summary of only a few of the historical Indian Ocean tsunamis (Further information on Indian Ocean earthquakes and tsunamis will be provided with subsequent updates).

The Earthquake and Tsunami of 31 Dec 1881 in the Andaman Sea

A major earthquake (with estimated Richter magnitude of 7.9 ) in the vicinity of Car Nicobar island, in the Andaman Sea, generated a destructive tsunami which must affected the entire Andaman and Nicobar island group, and quite possibly the entire Bay of Bengal region. Waves of 1 meter height were recorded by a tide gauge station at Chennai, on the East coast of India. Additional documentation will be provided with a later update

The Earthquake and Tsunami of 26 June 1941 in the Andaman Sea

On June 26, 1941 (11:52:03 UTC), a devastating earthquake (Mw 7.7 , Mb 8.0, Ms 7.7) occurred in the Andaman Sea. Its epicenter was at 12.50 degrees North and 92.57 degrees East - about 9 degrees North of the epicenter of the 26 December 2004 earthquake, but within its tsunami generating area. This was the greatest earthquake in the Andaman and Nicobar Islands since the 31 December 1881 earthquake (M7.9) in the Nicobar Islands.

The 1941 earthquake was particularly destructive in the Middle and South Andaman Islands and caused considerable damage at Port Blair, Port Anson and surrounding areas. The earthquake ground motions were strong enough to be felt along the eastern coast of India, in Calcutta (now Kolkata), Chandernagar, Cuttack, Madras (now Chennai), in Colombo, Sri Lanka , and at Syhlet in Bangladesh. A series of strong aftershoks (two with magnitude 6.0 ) occurred within 24 hours of the main earthquake. Fourteen more earthquake aftershocks with magnitude 6.0 occurred until January 1942.

The earthquake generated a tsunami in the Bay of Bengal, but no estimates of wave heights are available According to reports, more than 5,000 people were killed on the east coast of India. The media incorrectly attributed the deaths and damage to storm surges rather than to a tsunami generated by an earthquake. Many more deaths must have occurred elsewhere but were not reported. World War II was in progress and communications were poor. Because of the war, losses of lives in remote areas from disasters did not get as much attention or media coverage. It is suspected that this tsunami caused many more deaths than what was reported. This event remains to be further investigated.

The Earthquake and Tsunami of 28 November 1945 in the Northern Arabian Sea

A great earthquake with moment magnitude Mw 8.0 (Richter Ms 7.8), occurred on 28 November 1945 (21:56 UTC) off the Makran coast of Pakistan. Its epicenter was at 24.5 N 63.0 E in the northern Arabian Sea, about 100 km south of Karachi. The earthquake generated a very destructive tsunami which affected Pakistan, the western coast of India, Iran and Oman, killing thousands of people and causing a great deal of destruction.

The tsunami was genetated along an active subduction zone off the Makran coast of Pakistan. This zone marks the boundary between the Arabian plate sliding beneath the Iranian micro-plate. A major fault which runs along the Makran coast is believed to be of the same character as the West Coast fault along the coast of Maharashtra, India.

The region of subduction along the Makran coast of Pakistan and the Gujarat Region of India where major earthquakes have occurred - one as recently as 2001.

PAKISTAN - The tsunami waves reached a maximum height of 40 feet along the Makran coast destroying fishing villages and causing great damage to port facilities. More than 4,000 people died from the combined earthquake and tsunami along the Makran coast, but most of the deaths were caused by the tsunami.

 

Tsunami waves of about 6.5 feet in height struck Karachi. There was no damage to the port and boats in Karachi Harbour. According to reports, the waves completely destroyed and killed all the people of the fishing village of Khudi, some 30 miles west of Karachi. There was considerable destruction and loss of life at the towns of Pasni and Ormara.

IRAN - There was considerable loss of life and destruction but no details are available.

INDIA - There was extensive destruction and loss of life along the west coast of India {(Salsette Island , Versova (Andheri), Haji Ali (Mahalaxmi), Juhu (Ville Parle) and Danda (Khar)}. The tsunami waves reached a height of 11.0 - 11.5 meters in Kutch, Gujarat. In Mumbai the height of the tsunami was 2 meters. The waves were recorded in Bombay Harbor but did not cause damage.

OMAN - There was considerable loss of life and destruction but no details are available. The tsunami was recorded at Muscat and Gwadar.

Future destructive tsunamis in the region could be generated from earthquakes along the subduction zone off the Makran coast or from a a major thrust fault along parts of deltaic Indus river.

(Excerpts from unpublished report by G. Pararas-Carayannis, "Seismo-Dynamics of Compressional Tectonic Collision - Potential for Tsunamigenesis Along Boundaries of the Indian, Eurasian and Arabian Plates" (Abstract submitted to the International Conference HAZARDS 2004, Hyderabad, India, 2-4 Dec. 2004 )

The Earthquake and Tsunami of 19 August 1977 in Indonesia - (Source: George Pararas-Carayannis 1977 survey in ITIC and ISU reports and Newsletters)

On August 19, 1977 (06:08:52.2 UTC) a major earthquake {Magnitude: 8.22 (Mw), 8.1 (Ms), 8.9 (ML)} occurred in the Java Trench, westward of Sumba Island in Indonesia. This was the strongest earthquake in the Indian Ocean in several decades.The epicenter was 170 kilometers SSW of Pradapare (Sumba Island), at 11.09 S, 118.46 W. The quake was very widely felt and caused people in Perth, Australia, more than 2000 Km southward, to flee from office buildings. A major tsunami was generated which struck the coast of Sumba, Sumbawa, Lombok and Bali. In Kuta - Bali, one person was killed and 5 houses collapsed, 26 boats were broken or missing. On Lombok, 20 persons were killed, 115 houses damaged, 132 boats missing or broken. On Sumbawa, 81 people were killed, 53 people missing, more than 1000 people lost their properties, 63 houses, one school building, one mosque collapsed and the other was cracked. The quake also caused damage to some office buildings, school buildings, a mosque and a market in Sumbawa and Bima. In the entire Nusa Tenggara Islands region, the quake caused 107 deaths, with 54 people missing, 440 houses damaged/collapsed, 467 boats missing or broken, 5 school buildings collapsed and 3 teachers houses damaged.

The Lesser Sunda Islands where the 19 August 1977 Earthquake and Tsunami Occurred

Coastal roads did not exist in 1977 along the shores of the Lesser Sumba Islands fronting the Java Trench, but with the exception of Sumbawa some communities could be reached by road from the interior. Thus, no major ports were in the seriously struck areas, and casualties were relatively low. Incomplete reports indicated that more than 180 people died or presumed to be dead and that 3900 were left homeless. Property losses included homes, fishing boats, and gear. No tide records were available for most areas in Indonesia. However, on an inaccessible section of Sumbawa Island, a preliminary study indicated that the waves reached at least 15 meters above high tide, and penetrated about 500 meters inland in some valleys. Accounts given of the tsunami by observers at several locations have reasonable consistency.

The tsunami arrived on the Indonesian coast about an hour or two after high water, and begun with a recession that exposed the beach for 100-200 meters. Three large waves followed at intervals of perhaps 5 minutes or less, the first being the highest and most destructive. Residents in Sumbawa and Lombok communities reported that that before the quake and the tsunami arrival up to 3 unusual explosive sounds were heard over a period estimated from a few seconds to a minute or more. The sounds were described as those of bombs, of aircraft breaking the sound barrier, or thunder. The sound in each case came more or less from the direction of the earthquake's epicenter at sea. Almost every community reported the water turning black, and some claimed also that it increased in temperature and bad a bad odor.

Three major waves reportedly struck along the Australian coast ,the first being the largest, as in Indonesia. The sea level disturbances continued for several hours. The wave height was 2 meters at Dampier, 2 to 4 meters at Port Sampson, and 6 meters at Cape Leveque. The tsunami arrived as the tide was falling and, at most places, it was near low - which fortunately reduced the tsunami impact. There was apparently no loss of life in Australia, though it was reported that at least one person was swept into the sea by the waves.

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