September 2007 Sumatra earthquakes

Earthquake
title=September 2007 Sumatra earthquakes
date= September 12, 2007

---

Map showing the 3 large quakes and 22 pre and aftershocks in a span of 24 hours.
magnitude = 8.5 M_w [http://www.alertnet.org/thenews/newsdesk/N12258139.htm Indonesia quake was 8.4 magnitude, says USGS] , Reuters]
depth=30 kilometres
location=coord|4.520|S|101.374|E
countries affected = flag|Indonesia
flag|Singapore
flag|Malaysia
flag|Thailand
casualties = 23 killed [The Jakarta Post. [http://www.webcitation.org/5RtsfHEFK "Death toll from Indonesian quake reaches 23 as villagers start returning home"] , September 16 2007]

The September 2007 Sumatra earthquakes were a series of earthquakes that struck the Java Trench off the coast of Sumatra, Indonesia, three greater than magnitude 7. A series of tsunami bulletins was issued for the area.

Timeline

The first earthquake occurred at 11:10:26 UTC (18:10 local time) on 12 September 2007, and was an 8.5 M_w earthquake on the moment magnitude scale. It was centered about 34 km underground, at coord|4.520|S|101.374|E, about 130 km southwest of Bengkulu on the southwest coast of Sumatra, Indonesia, and some 600 km west-northwest of Indonesia's capital city, Jakarta. It was followed by several earthquakes of magnitude 5 through 6 along the same fault, west of Sumatra.

The second largest earthquake, 7.9 M_w, [ [http://earthquake.usgs.gov/eqcenter/recenteqsww/Quakes/us2007hec6.php KEP. MENTAWAI REGION, INDONESIA] , USGS] occurred later the same day at 23:49:04 UTC (06:49:04 local time the following day). It was centred about 10 km underground, at coord|2.506|S|100.906|E, some 185 km (115 miles) south-southeast of Padang, Indonesia and about 205 km northwest of Bengkulu (about 225 km northwest of the magnitude 8.5 earthquake).

After further aftershocks above magnitude 5, a third earthquake, 7.0 M_w, [ [http://earthquake.usgs.gov/eqcenter/recenteqsww/Quakes/us2007hfax.php Magnitude 7.0 - KEPULAUAN MENTAWAI REGION, INDONESIA] , USGS] occurred at 03:35:26 UTC (10:35:26 local time) on 13 September. It was centred about 10 km underground, at coord|2.160|S|99.851|E, some 165 km south-southwest of Padang and 345 km west-northwest of Bengkulu.

Aftershocks continued into 13 September and 14 September , with more earthquakes ranging up to magnitude 6.4. [ [http://earthquake.usgs.gov/eqcenter/recenteqsww/Quakes/quakes_big.php Latest Quakes +5.0M] USGS] Most of the aftershocks have been northwest of the original magnitude 8.4 earthquake.

Tidal buoys [ [http://www.ndbc.noaa.gov/station_page.php?station=23401 DART Buoy Station 23401 - 600 NM West-Northwest of Phuket, Thailand] ] positioned in the Indian Ocean and other seismic tools have led scientists to issue a series of tsunami bulletins. [ [http://www.prh.noaa.gov/ptwc/?region=3&id=indian.2007.09.13.002807 Message indian.2007.09.13.002807 Pacific Tsunami Warning Center, NWS] , NWS PTWC]

Effects

The tremors of the 8.5 M_w earthquake lasted for several minutes. It caused buildings to sway in Jakarta, and some buildings were reported to have collapsed in the city of Bengkulu, Province Bengkulu, about 100 km from the epicenter. Tremors felt in Jakarta were described as being "violent". [ [http://news.bbc.co.uk/2/hi/asia-pacific/6991294.stm Eyewitnesses: Sumatra earthquake] , BBC News] It was reported that several high-rise buildings were evacuated. [http://news.bbc.co.uk/2/hi/asia-pacific/6991134.stm Powerful quake shakes Indonesia] , BBC News] At least one person was killed, having been struck by a falling tree during evacuation, and dozens were injured. The earthquake also led to a power outage in Bengkulu, which has crippled communications. Consequently, the extent of damage in areas near the epicenter remains largely unknown. The death toll of the earthquakes is 21 with 88 people injured. [ [http://www.alertnet.org/thenews/newsdesk/SP40512.htm Reuters AlertNet - Indonesia quake toll rises to 21 dead, 88 wounded ] ]

Tremors were felt in neighbouring countries as far away as Southern Thailand. [ [http://www.channelnewsasia.com/stories/afp_asiapacific/view/299424/1/.html Tsunami alert issued after Indonesia quake: US centre] ] [ [http://pasadena.wr.usgs.gov/shake/ous/STORE/X2007hear/ciim_display.html Event 2007hear: View Map] ] In Singapore, which is about 670 km from the epicenter, the tremor was felt at around 11:10 UTC (19:10 local time). [ [http://www.channelnewsasia.com/stories/singaporelocalnews/view/299419/1/.html Singapore buildings sway after strong quake hits Indonesia] ] Most of the Central and Eastern part of Singapore has felt the tremor. [ [http://www.channelnewsasia.com/tremor/map.htm Map] ] In Peninsular Malaysia, tremors were reported after 19:15 local time, including Kuala Lumpur, Putrajaya, Johor Bahru, Malacca and Penang. Like Singapore, the tremors were most severe on high-rises, resulting in minor panic and evacuations. No casualties were reported in the country, as of September 13.cite web |url=http://www.sun2surf.com/article.cfm?id=19325 |title=8.2 magnitude quake sparks tsunami warnings |accessdate=2007-09-13 |author= |date=2007-09-13 |publisher=Sun2Surf ] cite web |url=http://www.thestar.com.my/news/story.asp?file=/2007/9/13/nation/18874029&sec=nation&focus=1 |title=Quake felt in Malaysia |accessdate=2007-09-13 |author= |date=2007-09-13 |publisher="The Star" ]

Tsunami

Sea level readings indicated that a tsunami was generated. A total of 4 tsunami alerts were issued in 24 hours. After the first, and largest, earthquake, the Pacific Tsunami Warning Centre issued a tsunami alert for much of the Indian Ocean basin. A tsunami approximately 1 metre high was reported at Padang, Indonesia. [ [http://www.thejakartapost.com/detailgeneral.asp?fileid=20070912203110&irec=2 Powerful earthquake triggers tsunami in western Indonesia] , "The Jakarta Post"] A small tsunami, some 15 cm high, was reported at the Cocos Islands. [ [http://www.news.com.au/heraldsun/story/0,21985,22410200-5005961,00.html Tsunami recorded at Cocos Island] , Herald Sun] Sumatra was taken off tsunami alert after two hours.

Tsunami warnings were also issued in India and other countries around the Indian Ocean soon after the earthquake. The Government of India asked the states of Tamil Nadu, Kerala, Andhra Pradesh and the union territories of Andaman and Nicobar Islands and Puducherry to be on high alert. [ [http://www.ibnlive.com/news/india-on-tsunami-alert-after-quake-near-indonesia/48531-2.html India on tsunami alert after quake near Indonesia] , "CNN-IBN"] By late September 12, the tsunami warning was recalled. [ [http://www.hindu.com/2007/09/13/stories/2007091357940100.htm Tsunami alert withdrawn] . "The Hindu"] Similarly, a tsunami alert was issued in Peninsular Malaysia at 20:50 (local time) for the coastal areas of Perlis, Kedah, Perak and Penang; the alert was lifted two hours later. However, Malaysian authorities had detected a 1-3m high tsunami heading away from the epicenter of the earthquake.

Tectonic summary

According to the US Geological Survey, [http://earthquake.usgs.gov/eqcenter/recenteqsww/Quakes/us2007hear.php#summary Magnitude 8.5 - Southern Sumatra, Indonesia] ] the earthquake was caused by thrust faulting on the boundary between the Australian Plate and the Sunda Plate. At the location of the earthquake, offshore of the west coast of Sumatra, the Australia plate moves northeast with respect to the Sunda Plate at a velocity of about 69 mm/year, oblique to the orientation of the plate boundary. The component of plate motion perpendicular to the boundary produces thrust faulting on the offshore plate-boundary.

The magnitude 7.9 earthquake was also a result of thrust faulting on the same plate boundary. It occurred about 225 km northwest of the magnitude 8.4 earthquake, at the northern end of the aftershock zone. [ [http://earthquake.usgs.gov/eqcenter/recenteqsww/Quakes/us2007hec6.php#summary Magnitude 7.9 - KEPULAUAN MENTAWAI REGION, INDONESIA ] ]

The magnitude 8.5 earthquake was the most powerful earthquake of 2007 to date, more powerful than the two March 2007 Sumatra earthquakes nearby and the 2007 Peru earthquake. It was the second most powerful earthquake since the magnitude 9.3 2004 Indian Ocean earthquake, exceeded only by the magnitude 8.6 2005 Sumatra earthquake. The two largest earthquakes were the fourth and fifth earthquakes with magnitude 7.9 or greater to have occurred on or near the plate boundaries offshore of western Sumatra in 7 years, the others being the magnitude 7.9 earthquake of June 4, 2000; the magnitude 9.3 2004 Indian Ocean earthquake on December 26, 2004; and the magnitude 8.6 2005 Sumatra earthquake on March 28, 2005.

According to data from the Japanese PALSAR microwave sensor aboard the Daichi(ALOS) satellite, South Pagai Island was uplifted, creating 6 new islands, and exposing previously submerged coral reefs as well as enlarging existing islands. [ja icon [http://cais.gsi.go.jp/Research/topics/topic071001/rgb_e.html Southern Sumatra Earthquake in 2007, coastal change, GSI ] ]

References

External links

* [http://earthquake.usgs.gov/eqcenter/recenteqsww/Quakes/us2007hear.php USGS Earthquake Center 8.5 tracking report]
* [http://earthquake.usgs.gov/eqcenter/recenteqsww/Quakes/us2007hec6.php USGS Earthquake Center 7.9 tracking report]
* [http://earthquake.usgs.gov/eqcenter/recenteqsww/Quakes/us2007hfax.php USGS Earthquake Center 7.0 tracking report]
* [http://wcatwc.arh.noaa.gov/message622582-01.htm Tsunami Information Statement #1] , NOAA/NWS/West Coast and Alaska Tsunami Warning Center
* [http://www.prh.noaa.gov/ptwc/messages/indian/2007/indian.2007.09.12.123044.txt Tsunami bulletin number 003] , Pacific Tsunami Warning Center/NOAA/NWS