Everything about The September 2007 Sumatra Earthquakes totally explained
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
Mw 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, 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
Mw, occurred at 03:35:26 UTC (10:35:26 local time) on
13 September. It was centred about 10 km underground, at, 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. Most of the aftershocks have been northwest of the original magnitude 8.4 earthquake.
Tidal buoys positioned in the
Indian Ocean and other seismic tools have led scientists to issue a series of tsunami bulletins.
Effects
The tremors of the 8.5
Mw 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". It was reported that several high-rise buildings were evacuated. 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.
Tremors were felt in neighbouring countries as far away as
Southern Thailand. In
Singapore, which is about 670 km from the epicenter, the tremor was felt at around 11:10 UTC (19:10
local time). Most of the
Central and
Eastern part of
Singapore has felt the tremor. 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.
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. A small tsunami, some 15 cm high, was reported at the
Cocos Islands. 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. By late
September 12, the tsunami warning was recalled. 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. 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.
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.
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