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

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THE EARTHQUAKE AND TSUNAMI OF 17 JULY 2006 IN SOUTHERN JAVA, INDONESIA

George Pararas-Carayannis

The Earthquake

A major earthquake off the southern coast of the Island of Java in Indonesia generated a destructive tsunami. Most of the deaths and damage were caused by the tsunami.

 

Earthquake Origin Time, Magnitude, Epicenter and Focal Depth

The earthquake with a moment magnitude of 7.7 occurred on Monday, July 17, 2006 at 08:19:25 (UTC - Coordinated Universal Time) or 3:19 PM local time in Indonesia. According to the US Geological Survey (NEIC) the quake's epicenter was at 9.334 S, 107.263 E along the southern coast of the Island of Java, in Indonesia - about 355 km (220 miles) South of Jakarta, 265 km (165 miles) south of Bandung (Java), 245 km (155 miles) SSW of Tasikmalaya (Java), 225 km (140 miles) NE of Christmas Island and about 180 km (110 miles) off the coastal area of Pangandaran.

 

Aftershocks

Following the major earthquake event there three strong aftershocks over the next three hours, followed by a series of many more in subsequent hours.

Felt Reports

The earthquake was strongly felt hundreds of miles away in Jakarta where tall buildings swayed. The Modified Mercalli intensity was IV at Bandung, Jakarta, Pangandaran and Tasikmalaya; It was III at Cianjur and II at Karangkates, Sawahan and Yogyakarta. It was also felt at Bantul, Banyumas, Ciamas, Cilacap, Garut, Kebumen, Sukabumi and Surabaya. However, many residents along the coast said that they did not feel the quake's motions before the tsunami struck. However, others claimed that they did feel the earthquake but did not realize that a tsunami had been generated until the heard the roar of the first wave.

Death Toll and Damages

The earthquake and tsunami killed at least 600 people and injured 431 people across six districts along Central and West Java provinces. More than 230 are still missing and feared dead. The death toll is expected to rise. Most deaths were caused by the tsunami along coastal fishing villages and along the beaches at the Pangandaran resort in West Java's Ciamis district, about 270 kilometers (170 miles) southeast of
Jakarta. A total of 68,464 people were displaced.

Recent Earthquakes near Java

Earthquakes occur very frequently in all the islands of Indonesia, in the inland seas, and along the Great Sunda Trench. The region near and south and east- southeast of Java has produced several earthquakes in recent times.

Satellite photo of the Island of Java


On 27 May 2006, a shallow 6.3 magnitude earthquake near the city of Yogyakarta in central Java killed more than 6,000 people and displaced more than 200,000. A major earthquake (magnitude 7.8) on 2 June 1994 generated a tsunami that killed more than 200 people. An even greater earthquake (magnitude 8.3) on 20 August 1977, about 1200 km east-southeast of the 17 July 2006 event, generated a destructive tsunami that also killed about 200 people.

 

 

 

Tectonic Setting

The Indonesian region is one of the most seismically active zones on earth. It is an island-arc structure of about 17,000 islands spread out along a belt of intense volcanic and seismic activity. Such tectonic features characterize the region as a deep oceanic trench on the Indian Ocean side, a geanticline belt and volcanic inner arc, and several marginal basins. Also, the region has about 400 volcanoes, of which about 100 are active. The best known of the volcanoes is Krakatau in the Sunda Strait, between Java and Sumatra. The 1883 explosion and collapse of the volcano generated an enormous tsunami that killed close to 37,00 people.


Subduction of the India plate beneath the Burma plate caused the great earthquake and the devastating tsunami of 26 December 2004 along the western coast of the island of Sumatra. Another great tsunamigenic earthquake occurred on 28 March 2005 near Nias Island off the coast of Sumatra.


Subduction of great tectonic plates continues further south and east/southeast along the great Sunda Trench. The entire region, but particularly Java, is tectonically unstable. The offshore region of southern Java has high seismicity and has produced many destructive earthquakes - some of which have generated destructive tsunamis. The offshore seismic activity along the southern coast of Java results from oblique subduction, as the Australia plate slides beneath the Sunda plate at a about 60 mm/yr in a north-northeastward direction.


Oblique subduction of tectonic plates at high rates along Eastern Indonesia has created a very complex active tectonic zone. As indicated, the rate of subduction in the West Java Trench where the 17 July 2006 earthquake occurred is about 60 mm/year. Further east along the East Java Trench the rate of subduction is about 50 mm/yr. Near New Guinea the subduction rate increases to as much as 107 mm/yr. Thus, major and great earthquakes occur frequently in this region.


The Tsunami of 17 July 2006 in Southern Java

The major earthquake of 17 July 2006 generated a destructive local tsunami that impacted about 129 miles of the southern coast of the Island of Java. Tsunami waves of up to 5 meters in height swept through fishing villages and resorts on Indonesia's Java Island destroying houses, restaurants, hotels, boats, and spreading devastation half a km inland. The death toll rose to more than 600, with hundreds more missing. The death toll is expected to climb. More than 54,000 people were displaced.

Tsunami Warning issued but not disseminated

Both the Pacific Tsunami Warning Center in Honolulu and the Japan Meteorological Agency sent warning bulletins to authorities in Indonesia 45 minutes before the tsunami struck Java. However the warnings were not announced and the people in the threatened area were not notified. The authorities did not announce the warnings because they did not want to cause unnecessary alarm.


To this day - in spite of the 2004 devastating tsunami that killed more than 250,000 people in the countries of the Indian Ocean, including 170,000 in Indonesia - there is still no operating local system of sirens, alarms, or other type of communication on the island of Java that can provide effectively warnings to people along vulnerable coastlines. In the year and a half following the 2004 tsunami disaster, all efforts to install an early warning system have concentrated on the Island of Sumatra and deep ocean sensors are in place off the coast. However, even this system is not yet fully operational and no tsunami warning system has been set up yet for the southern coast of Java - although one is planned for completion by 2007.

Tsunami Travel Time and Extent of Inundation

According to eyewitnesses the first wave reached the nearest shore of southern Java within half hour after the earthquake. Subsequent larger waves reached about half a km (300 yards) inland.

Tsunami Effects

Waves of up to four to five meters struck the coastline along the southern coast of the island of Java. The waves were particularly destructive along the Pangandaran coast.

Pangandaran: Hardest hit by the tsunami were the beaches at Pangandaran - a resort community near Ciamis town, 270 km (170 miles) southeast of Jakarta. Waves up to 5 meters high crashed and swept cars, motorbikes and boats into hotels and storefronts, flattened homes and restaurants, and flooded rice fields up to 500 meters (550 yards) from the sea along a stretch of the densely populated coastline. Most of the reported deaths occurred in this area.

Batu Keras Beach: According to eyewitnesses at Batu Keras beach, 30 kilometers west of Pangandaran, the water withdrew for about 5 minutes and people on the beach, instead of running to higher ground, went out to look at stranded fish - just before the first roaring wave hit the shoreline at about 4.30 p.m., local time. A total of six waves were reported - the second being the biggest and as high as four to five meters.

Ciamis: in the town of Ciamis, 270km southeast of Jakarta in West Java, the larger hotels around the beach remained standing, but many of the smaller buildings and dozens of homes were destroyed. Many people lost their lives.

Tsunami Destruction at Pangandaran

Port of Cilacap: Extensive damage occurred at the central Java port of Cilacap and many people were killed.

Satellite photo showing extent of the tsunami inundattion along part of Pangandaran Beach taken on July 19, 2006 by the commercial satellite ICONOS.

Cristmas Island: The tsunami registered a maximumum height of 60 centimeters/

Tsunami Generating Mechanism

The 17 July 2006 tsunami was generated by thrust faulting along the boundary between the Australia plate and the Sunda plate.

 

Past Tsunamis in Java, near Java and East of Java

Several destructive tsunamis have occurred in this region in the past.

East Java - June 2, 1994

A large, shallow thrust, major earthquake (with moment magnitude of 7.8) off the southeastern coast of Java - near the east end of the Java Trench in the Indian Ocean - generated a devastating tsunami (which was much larger than expected for the size of the earthquake). Twenty to thirty minutes after the main shock, tsunami waves arrived at the nearest coasts. The most severe tsunami damage occurred along the southern coast of East Java where waves ranging in height from 1-14m. Along the southwestern coast of the Island of Bali the waves ranged from 1-5 meters. In total, 223 persons lost their lives, approximately 400 were injured, and over 1000 houses were destroyed.

Flores Island - 12 December 1992

An earthquake of magnitude 7.8, with epicenter about 35 km NW off the north coast of the eastern part of Flores Island near Maumere - its largest city - generated a local tsunami which killed 1690 people and destroyed approximately 18,000 houses. The tsunami's first wave arrived on the shores of Flores within two minutes after the initial shock, and reached the north shore within five minutes. Huge waves with runup of up to 26.2 m completely overrun and destroyed Riang-Kroko, a small village at Cape of Watupajung at the extreme NE end of Flores Island, killing 137 people.


Elsewhere on Flores Island the tsunami runup ranged form 2 to 5.2 m, peaking at Kolisia village, an area which also experienced maximum subsidence from quake ground movement. Tsunami waves of up to 2.9 meters completely inundated the small, densely populated village of Wuhring (Wuhring island), located on a low spit about 3 km NW of Maumere. The waves destroyed most of the houses and killed 87 of the 1400 people living there. Waves with runup of up to 4.6 m also overrun the low lying village of Nebe on Flores island, destroying nearly all the homes and killing two people. On the island of Babi, located about 40 km NE of Maumere, waves with maximum runup of 5.6 m killed 263 of the island's 1,093 inhabitants.

Lesser Sunda Islands - Sumba, Sumbawa - 19 August 1977

On August 19, 1977 a great earthquake (moment magnitude 8.3)occurred in the Java Trench, westward of Sumba Island. 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. The tsunami arrived on the Indonesian coast about an hour or two after high water, and commenced with a recession that frequently left an additional 100-200 meters of beach exposed. Three large waves followed at intervals of perhaps 5 minutes or less, the first being, the highest and most destructive, with a maximum run-up height of 15 meters. The waves penetrated about 500 meters inland in some valleys and killed almost 200 people and left 3900 homeless.


An unusual feature was that between the time of the quake and the tsunami arrival residents in Sumbawa and Lombok communities heard up to 3 explosive sounds, over a period estimated from a few seconds to a minute or more, and these were described variously as sounding like bombs, aircraft breaking the sound barrier, or thunder. The sound in each case came more or less from the direction of the epicenter. Almost every community reported the water turning black, and some claimed also it increased in temperature and bad a bad odor.


Along the Australian coast, as in Indonesia ,three major waves came in with the first being the largest. A wave height of 2 meters was reported at Dampier, 2 to 4 meters at Port Sampson, and 6 meters at Cape Leveque. The tide was falling and, at most places, it was near low and this reduced the tsunami impact. There was apparently no loss of life in Australia, though it is reported that at least one person was swept into the sea by the waves.The disturbance continued for a number of hours.

REFERENCES - Additional Sources of Background Information

Hamilton, W., 1979, Tectonics of the Indonesian region: U.S. Geological Survey Prof. Paper 1078.


Pararas-Carayannis, G. International Tsunami Information Center
A Progress Report For 1974-1976. International Coordination Group for the Tsunami Warning System in the Pacific, Vina Del Mar, Chile, 1977.

Pararas-Carayannis, George, International Tsunami Information Center,Tsunami Report 77-12 ,
Tsunami Reports for 1977.

Pararas-Carayannis, G., Indonesian Earthquake and Tsunami of August 19, 1977, Intern. Tsunami Information Center Report, Abstracted article in Tsunami Newsletter, Vol. X, No. 3, September, 1977.

Pararas-Carayannis, G. 1989. Five-Year Plan for The Development of A Regional Warning System in the Southwest Pacific. A Report prepared to the United Nations Development Program (UNDP), New York, May 1989, 21 p. _

Pararas-Carayannis, G. 2004. TSUNAMI INFORMATIONAL KIT Prepared for UNESCO-INTERGOVERNMENTAL OCEANOGRAPHIC COMMISSION. Sept. 2004

Pararas-Carayannis, G., The Great Earthquake and Tsunami of 28 March 2005 in Sumatra, Indonesia
http://drgeorgepc.com/Tsunami2005ndonesia.html

Pararas-Carayannis, G. The Great Earthquake and Tsunami of 26 December 2004 in Southeast Asia and the Indian Ocean
http://drgeorgepc.com/Tsunami2004Indonesia.html

Pararas-Carayannis, G. NEAR AND FAR-FIELD EFFECTS OF TSUNAMIS GENERATED BY THE PAROXYSMAL ERUPTIONS, EXPLOSIONS, CALDERA COLLAPSES AND MASSIVE SLOPE FAILURES OF THE KRAKATAU VOLCANO IN INDONESIA ON AUGUST 26-27, 1883, Presentation for the International Seminar/Workshop on Tsunami "In Memoriam 120 Years Of Krakatau Eruption _ Tsunami And Lesson Learned From Large Tsunami" August 26th _ 29th 2003, Jakarta and Anyer, Indonesia. Also published in the Journal of Tsunami Hazards, Volume 21, Number 4. 2003

http://www.STHJOURNAL.ORG
http://drgeorgepc.com/Tsunami1883Krakatau.html

Pararas-Carayannis, G. The Great Tsunami of August 26, 1883 from the Explosion of the Krakatau Volcano ("Krakatoa") in Indonesia
http://drgeorgepc.com/Tsunami1883Krakatoa.html

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