7/17/2006 Java Tsunami

Updated 7/18/2006

A Magnitude 7.7 earthquake, which occurred at 08:19 GMT, 15:19 local time July 17, 2006, under the ocean South of the Indonesian island of Java triggered a tsunami that hit the south Java coast barely an hour later. The epicenter of the quake was 225 miles south of Jakarta and 225 miles SW of Yogyakarta, which was hit by a earthquake on May 26 that killed more than 5800 people. This earthquake itself caused only light to moderate shaking throughout Java, however tsunami waves over 2 meters high arriving without warning most places claimed 341 lives with 250 people still missing and 42,000 displaced. Eyewitnesses reported a black wall of water that swept inland smashing boats, houses, businesses and coastside resorts.

The Indonesian government said that many people fled inland when they felt the earthquake, which is what experts advise, but many did not realize the danger of tsunami and even followed receding water out onto the seabed only to be caught when the waves came in. The water came as far as half a kilometer inland. Initial reports indicated heavy damage in the resort of Pangandaran, although likely much of the coast was affected to some degree.

According to the USGS, "The earthquake occurred as a result of thrust-faulting on the boundary between the Australian Plate and the Sunda Plate. On this part of their mutual boundary, Australian Plate moves NNE with respect to the Sunda Plate at about 59 mm/year. The Australian Plate thrusts beneath the Sunda Plate at the Java Trench, South of Java, and is subducted to progressively greater depths beneath Java and North of Java. The earthquake occurred on the shallow part of the plate boundary about 50 Km north of the Java Trench. ... This year's May 26 devastating Yogyakarta earthquake, Magnitude 6.3, occured at shallow depth within the overriding Sunda Plate."

(See the Plate Tectonics page for more information on these processes.) The US Geological Survey (USGS) is an invaluable resource in understanding and tracking earthquakes.

US Geological Survey page on this quake

See also the following news stories:

5/27/06 Java Quake

Updated 7/8/06

At 5:54 AM local time Saturday Morning May 27, 2006 (22:53 GMT Friday) a 6.3 Magnitude earthquake hit near the south coast of central Java in Indonesia. It was centered near the major city of Yogyakarta, 275 miles SE of Jakarta. Yogyakarta, (sometimes spelled Jogjikarta, or Jogji) is one of the major cities of Indonesia. About 5 million people live within 50 kilometers of the epicenter. A point of interest is that this is one of the few places that the pre-colonial government structure of a sultanate has survived. It is not known how the 18th Century Sultan's palace, a large architecturally significant building in the center of the city, has fared.

5,700 people have been killed and 36,300 injured according to the Indonesian government. People reported that this was by far the biggest quake that they had ever experienced. There was very extensive damage to buildings, especially in the hardest hit area south of the city in the Bantul area where the epicenter was located. Electricity and communications were been knocked out in the affected areas. The airport was closed due to damage to the runway and emergency flights had to come into the nearby city of Solo.

Hospitals were overwhelmed with the injured with temporary medical clinics set up in the streets. International aid has been offered by Russia, the Europeon Union and others. UNICEF said it is preparing emergency supplies and has sent staff to Yogyakarta. It has emergency supplies of tents, hygiene kits, health kits and school supplies available to be sent to the earthquake zone. The supplies include 9,000 tarpaulins, 850 hygiene kits, 1,165 small tents, 753 large tents, 4,000 lanterns, 160 collapsible water tanks, 1,707 school kits, 50 school tents, 152 recreation kits, and 90 school-in-a-box school supplies

Thousands of people fled inland immediately after the quake to escape a possible tsunami. This was a lesson learned after the 2004 tsunami. Although this quake was very much smaller and did not pose a tsunami threat, it was not immediately clear to people on the scene that this was the case. This self evacuation is exactly what earthquake experts recommend to people living in coastal areas who experience an earthquake. As we saw in 2004, waiting for official instructions would take too long and could prove fatal if there were to be a tsunami. They say that if you live near the coast and feel an earthquake, you should immediately move inland, as people did in this case.

The Mount Merapi volcano is just north of that area. Merapi has been erupting during the last few weeks. Many people have been evacuated from the volcano slopes for fear of a larger eruption with catastrophic landslides or lava flows. The earthquake appears to be unrelated to the eruptions, caused rather by normal tectonic processes but may be responsible for increased volcanic activity afterwards.

This quake was caused by the same plate interactions responsible for the 2004 earthquake and tsunami, although this quake was smaller (maybe 1/1000th as strong) than in 2004 and about 1200 miles to the south and east of that quake. This quake did not cause a tsunami. In general, the Indonesian archipeligo, especially Sumatra and Java, are formed by the subduction of the Australian Plate beneath the Eurasian plate. The actual situation is more complicated due to the many adjoining plates in that area of the world. These plate interactions make these islands among the most active areas of the world for both earthquakes and volcanos. Earthquakes are the result of the surface plates rubbing against eachother in a jerky fashion as one plate pushes itself beneath another. Volcanos occur as the subducting plate is forced down into the earth's interior. When it hits the mantle the rock melts into magma, some of which rises to the surface in volcanos.

(See the Plate Tectonics page for more information on these processes.) The US Geological Survey (USGS) is an invaluable resource in understanding and tracking earthquakes.

See also the following news stories: