2006 Pangandaran earthquake and tsunami
UTC time | 2006-07-17 08:19:26 |
---|---|
ISC event | 10699442 |
USGS-ANSS | ComCat |
Local date | July 17, 2006 |
Local time | 15:19 local time (WIB (Indonesia Western Standard Time)) |
Duration | 185 seconds[1] |
Magnitude | 7.7 Mw[2][3] |
Depth | 25.3 km (15.7 mi)[2] |
Epicenter | 9°20′S 107°19′E / 9.33°S 107.32°E[2] |
Type | Thrust[1][4] |
Areas affected | Southern Java, Indonesia |
Total damage | $44.7 million[5] |
Max. intensity | MMI IV (Light)[1][6] |
Casualties | 668 dead, 9,299 injured, 65 missing[7][8] |
An
An abnormally slow rupture at the
Tectonic setting
The island of Java is the most densely populated island on Earth, and is vulnerable to both large earthquakes and volcanic eruptions, due to its location near the Sunda Trench, a convergent plate boundary where the Australian tectonic plate is subducting beneath Indonesia. Three great earthquakes occurred in the span of three years to the northwest on the Sumatra portion of the trench. The 2004 M9.15 Sumatra–Andaman, the 2005 M8.7 Nias–Simeulue, and the 2007 M8.4 Mentawai earthquakes produced the largest release of elastic strain energy since the 1957/1964 series of shocks on the Aleutian/Alaska Trench.[9]
The southeastern (Java) portion of the Sunda Trench extends from the Sunda Strait in the west to Bali Basin in the east. The convergence of relatively old oceanic crust is occurring at a rate of 6 centimeters (2.4 in) per year in the west portion and 4.9 cm (1.9 in) per year in the east, and the dip of the Benioff Zone (the angle of the zone of seismicity that defines the down-going slab at a convergent boundary) is around 50° and extends to a depth of approximately 600 kilometers (370 mi). Pre-instrumental events were the large to very large events of 1840, 1867, and 1875, but unlike the northwestern Sumatra segment, no megathrust earthquake has occurred on the Java segment of the Sunda Trench in the last 300 years.[10]
Earthquake
The earthquake was the result of
The large and damaging tsunami that was generated was out of proportion relative to the size of the event, based on its short-period
Intensity
In tsunami prone regions, strong earthquakes serve as familiar warnings, and this is especially true for earthquakes in Indonesia. Previous estimates of the tsunami hazard for the Java coastline may have minimized the risk to the area, and to the northwest along the Sumatran coast, the risk is substantially higher for tsunami, especially near Padang. Previous events along the coast of Java in 1921 and again in 1994 illustrate the need for an accurate assessment of the threat. The July 2006 earthquake had an unusually slow rupture velocity which resulted in minor shaking on land for around three minutes, but the intensity was very light relative to the size of the tsunami that followed.[7]
The earthquake produced shaking at Pangandaran (where the M6.3 2006 Yogyakarta earthquake was felt more strongly) of intensity III–IV (Weak–Light), intensity III at Cianjur, and II (Weak) at Yogyakarta. Further inland and farther from the epicenter, intensity IV shaking made tall buildings sway in Jakarta, but at some coastal villages where many of the casualties occurred, the shaking was not felt as strong. An informal survey of 67 people that were present at the time revealed that in at least eight cases, individuals stated that they did not feel the earthquake at all (a typical M7.7 earthquake would have been distinctly noticed at those distances). The unusually low felt intensities, along with the short period body wave magnitudes, were components of the event that narrowed its classification into that of a tsunami earthquake.[6]
Type
Tsunami earthquakes can be influenced by both the presence of (and lack of)
One of the initial characterizations of tsunami earthquakes came from seismologist
Warning
A tsunami warning system was not in operation at the time of the shock, but the Pacific Tsunami Warning Center (operated by the National Oceanic and Atmospheric Administration in Hawaii) and the Japan Meteorological Agency posted a tsunami watch, based on the occurrence of a M7.2 earthquake. The bulletin came within 30 minutes of the shock, but there was no means to transmit the warning to the people on the coast that needed to know. Many of those who felt the earthquake responded by moving away from the shore, but not with any urgency. The withdrawal of the sea that exposed an additional 5–10 meters (16–33 ft) of beach created an even more significant warning sign, but in some locations wind waves on the sea effectively concealed the withdrawal that signalled the approach of the tsunami.[12][13]
Tsunami
The earthquake and tsunami came on a Monday afternoon, a day after many more people were present on the beach, due to a major national holiday. The waves came a few tens of minutes after the shock (and were a surprise, even to lifeguards) and occurred when the sea level was approaching low tide which, along with the wind waves, masked the initial withdrawal of the sea as the tsunami drew near. Most portions of the south Java coast saw runup heights of 5–7 meters (16–23 ft), but evidence on the island of Nusa Kambangan indicated that a peak surge measuring 21 meters (69 ft) had occurred there, suggesting to researchers that the possibility of a submarine landslide had contributed to the magnitude of the tsunami in that area.[14]
Runup
Tsunami surge heights | ||
Location | Coordinates | Height |
---|---|---|
Dara Payung | 7°41′53″S 109°15′51″E / 7.69806°S 109.26417°E | 7.39 m (24.2 ft) |
Bulak Laut | 7°41′01″S 108°36′43″E / 7.68361°S 108.61194°E | 7.38 m (24.2 ft) |
Pameungpeuk | 7°40′5″S 107°41′26″E / 7.66806°S 107.69056°E | 5.98 m (19.6 ft) |
Batu Hiu | 7°41′31″S 108°32′09″E / 7.69194°S 108.53583°E | 5.44 m (17.8 ft) |
Pangandaran | 7°41′37″S 108°39′06″E / 7.69361°S 108.65167°E | 4.27 m (14.0 ft) |
Sindongkarta | 7°45′52″S 108°3′35″E / 7.76444°S 108.05972°E | 3.95 m (13.0 ft) |
Kato et al. 2007, p. 1,057 |
A 300 km (190 mi) portion of the southwest and south-central Java coast was affected by the tsunami, and resulted in around 600 fatalities, with a high concentration in Pangandaran. Two thousand kilometers (1,200 mi) to the southeast at the Steep Point area of western Australia, a runup of 2 m (6 ft 7 in) was measured, which was comparable to a similar runup in northern Oman from the 2004 Indian Ocean earthquake and tsunami, though in that case it was at a much greater distance of 5,000 kilometers (3,100 mi). Within three weeks of the event, scientists from five different countries were on the ground in Java performing a survey of the affected areas, including gathering runup (height above normal sea level) and inundation (distance the surge moved inland from the shore) measurements.[13]
The island of
Damage
Since the earthquake caused only minor ground movement, and was only lightly felt, all the damage that occurred on the island was due to the tsunami. Types of buildings that were affected were timber/bamboo, brick traditional, and brick traditional with reinforced concrete. Semi-permanent timber or bamboo structures that were based on a wooden frame were the most economical style of construction that were assessed following the disaster. A tsunami flow depth of 2 m (6 ft 7 in) usually resulted in complete destruction of these types of structures. A group of scientists that evaluated the damage considered the unreinforced brick construction as weak, because the performance of homes constructed in that style did not fare much better than the timber/bamboo variety. Hotels and some houses and shops that were of reinforced brick construction were far better off, because units that were exposed to a flood depth of 3–4 meters (9.8–13.1 ft) were considered repairable.[8]
Many wooden cafes and shops within 20 meters (66 ft) of the shore were completely removed by the tsunami at Pangandaran, and severe damage still occurred to unreinforced masonry that was within several hundred meters, but some hotels that were constructed well held up better. The villages of Batu Hiu and Batu Kara, both to the west of Pangandaran, experienced similar damage. Other severe damage was seen at Marsawah village, Bulakbenda, where all buildings had been removed down to their foundation within 150 meters (490 ft) of the water line, and even 300–500 m (980–1,640 ft) further inland there were many buildings that were totally destroyed. Witnesses reported that waves were breaking several hundred meters inland at that location.[12]
Response
Officials in Indonesia received information regarding the tsunami in the form of bulletins from the
Trained research teams were already on the ground on Java responding to the May earthquake and began a survey of more than one hundred Muslim farmers, plantation laborers, and fishermen (or those with fishing-related occupations) that were affected by the tsunami. Almost two thirds of the group reported that they lived in permanent structures made of wood, brick, or cement, while the remainder lived in semi-permanent facilities made from earth or stone. The government was cited as the first responder for water, relocation and medical assistance, and helping with the deceased. For rescue, shelter, clothing, and locating missing people, individuals were listed as the primary provider, but 100% of those surveyed replied that the government should be responsible for relief. Most of those requiring aid stated that they were given effective assistance within 48 hours and that they were satisfied with the help.[15]
See also
References
- ^
- ^ a b c ISC (2016), ISC-GEM Global Instrumental Earthquake Catalogue (1900–2009), Version 3.0, International Seismological Centre
- ^ Mori et al. 2010, p. 202
- ^
- ^ a b Mori et al. 2010, p. 203
- ^ a b Yulianto, E.; Setja Atmadja, C. M. (2009), "Predecessors of the 2006 South Java Tsunami", Estimating the recurrence interval and behavior of tsunamis in the Indian Ocean via a survey of tsunami-related sedimentation, Tsukuba International Congress Center: National Research Institute for Earth Science and Disaster Prevention, p. 19
- ^
- ^ ISBN 978-0-521-19085-5
- S2CID 129933598
- ^ a b Mori et al. 2010, p. 204
- ^ S2CID 129647228
- Georgia Institute of Technology (June 18, 2007). "Scientists report study results from 'stealth' tsunami that killed 600 in Java last summer" (Press release). Eurekalert!.
- ^ a b Bliss, D.; Campbell, J. (2007), The immediate response to the Java tsunami: Perceptions of the affected (PDF), Fritz Institute, pp. 2–6, archived from the original (PDF) on 2019-11-05
Sources
- Kato, T.; Ito, T.; Abidin, H. Z.; Agustan (2007), "Preliminary report on crustal deformation surveys and tsunami measurements caused by the July 17, 2006 South off Java Island Earthquake and Tsunami, Indonesia", Earth Planets Space, 59 (9): 1, 055–1, 059,
- Mori, J.;
Further reading
- Fan, W.; Bassett, D.; Jiang, J.; Shearer, P. M.; Ji, C. (2017), "Rupture evolution of the 2006 Java tsunami earthquake and the possible role of splay faults", Tectonophysics, 721: 143–150, hdl:1912/9479
External links
- M7.7 – south of Java, Indonesia – United States Geological Survey
- In pictures: Indonesian tsunami – BBC News
- 'Stealth' Tsunami That Killed 600 In Java Last Summer Had 65 Foot High Wave – ScienceDaily
- A comparison study of 2006 Java earthquake and other Tsunami earthquakes – University of California, Santa Barbara
- Tsunami Event – July 17, 2006 South Java – National Oceanic and Atmospheric Administration
- Deadly Java Tsunami Caused by Slow-Moving Quake – National Geographic Society
- Officials failed to pass on tsunami warning – The Guardian
- Indonesia’s 2 tsunami alert buoys were busted – NBC News
- The International Seismological Centre has a bibliography and/or authoritative data for this event.