Figure 1. Epicenter Location
Figure 1. Epicenter Location

General Information

On September 12, 2007 an earthquake of magnitude 8.4 shook the ground of Indonesia. The mainshock of the earthquake occurred Wednesday at 6:10PM local time (USGS). The epicenter was located just off the coast of the Sumatra island of Indonesia, approximately 80 miles southwest of the nearest large city, Bengkulu (BBC News). Figure 1 shows a map view of the epicenter location in relation to Sumatra (The New York Times).

Earthquake Description

The Southern Sumatra Earthquake occurred on the boundary of the Australian and Sunda plates, which is a convergent boundary (USGS). The depth of the earthquake in this location was measured to be relatively shallow at 18.6 miles deep (FOX News). In this area, thrust faulting is seen, which is the result of a compressing motion of the earth’s crust (USGS). A thrust fault is one where the rock above the fault line will move up and over the rock below the fault line. It is a perpendicular movement between the plate boundaries off the shore of Sumatra (USGS). In this case, the Australia plate is moving toward the Sunda plate and in the process it is diving below the Sunda plate (University of Kentucky). This thrust fault motion has an approximate velocity of 60mm a year at the Australia-Sunda boundary (USGS). There is also a parallel motion due in part by the strike-slip faulting seen on the Sumatra fault, which runs through the center of the Indonesian island (USGS). Strike-s
Figure 2. Map of Sunda Trench
Figure 2. Map of Sunda Trench
lip faults differ from thrust faults in that this motion is horizontal where the rocks on one side of a fault
will glide past the rocks on the other side of the fault. The Australian plate is moving northeast to the Sunda plate at an oblique angle, which is why both perpendicular and parallel motions are seen (USGS). As the Australian plate collides with the Sunda plate it is subducted below because it contains the oceanic lithosphere which is denser than the continental lithosphere. As a result of this subduction, the oceanic trench called the Sunda trench is formed. See Figure 2 (Andaman)

Effects

Although the epicenter of the earthquake was located near the town of Bengkulu, Sumatra, it was felt as far away as the Indonesian Capital Jakarta which is nearly 400 miles away (BBC News). After the magnitude 8.4 mainshock, a sequence of aftershocks began with 6.6 being the strongest recorded of the group (FOX News). A three foot tsunami was generated near the town of Padang by the earthquake though it reportedly did little damage (FOX News). As a result of the earthquake, there were both monetary and personal effects:

Monetary:

  • 52,522 buildings and roads damaged or destroyed (USGS) See Figure 3.(IFRC)
  • Power outages (USGS)
  • Telephone outages (USGS)
    Figure 3. Effects on Families
    Figure 3. Effects on Families

Personal:

  • 25 people killed (USGS)
  • 161 people injured (USGS)
  • Felt in Indonesia, Malaysia, Singapore, and Thailand (USGS)
  • Tsunami warnings issued
  • Evacuation

What was Learned from the 2005 Sumatra Earthquake:

One of the previously devastating earthquakes was on March 28th, 2005 where an earthquake of magnitude 8.7 hit the area of Sumatra, killing nearly 1,300 people and damaging numerous buildings and roads (EERI). Many of the casualties occurred from the initial earthquake motion; however, several others later arose because insufficient help was able to reach those in need.

Buildings that had collapsed in the quake were found to be made of combined weak materials such as half-burnt brick, timber, and concrete block (EERI). These buildings were seen to have low quality concrete and the detailing of how they were built was not up to code for earthquake-resistant construction requirements, causing them to fail as figure 4 shows (EERI). After the collapse of these buildings, it gave the region a chance to rebuild with higher standards and enforce the building codes to better withstand earthquakes to come, such as the September 2007 quake. Through the help of new technology, several homes had been rebuilt with bracing and
masonry.JPG
Figure 4. Masonry Building
columns to help support their structures (United Nations).

Along with the initial collapse of buildings, many roads and ports were destroyed in the Sumatra area, making it difficult to get help to the affected people. As a result, disaster preparedness programs are now in place to help educate people from Indonesia on what to do when disaster strikes, and where to go for help (Relief Web). In 2007, many more warehouses filled with supplies such as hygiene kits, lanterns, blankets, and medications were in place, ready to supply people. The Indonesian Red Cross was able to send volunteers to help within two hours of the earthquake occurring. They also set up field hospitals with several ambulances transporting people to them to reduce the number of deaths post-earthquake (Relief Web). In addition, wind-up radios were supplied to the area after the 2005 earthquake to provide people with warnings of tsunamis and also give information of where they could go to receive help once an earthquake has happened (UNDP).

Conclusion:

Although a number of lives were lost, the earthquake of September 12th, 2007 was relatively less damaging when compared with those earthquakes in the region from the past decade. It was reported by the USGS that in the past ten years there have been three other earthquakes of a magnitude 7.9 or larger in the same plate region where this one occurred. There have also been fifteen earthquakes of a magnitude of 6.3 or greater since 2004 where thousands of people have been killed as a result (CNN News). Improved disaster preparedness education and higher standards for structures will continue to make the loss one primarily of monetary value and less of human life.

Sources:

  1. Andaman. Image. March 3rd, 2005. http://www.andaman.org/BOOK/news_tsunami/2005_03Mar/faultlines.jpg
  2. BBC News. Powerful Quake Shakes Indonesia. September 12, 2007. http://news.bbc.co.uk/2/hi/asia-pacific/6991134.stm
  3. CNN. New Quake Rattles Indonesia. September 12, 2007. http://www.cnn.com/2007/WORLD/asiapcf/09/12/indonesia.quake/index.html
  4. EERI. Learning from Earthquakes. The Northern Sumatra Earthquake of March 28, 2005. http://www.eeri.org/lfe/pdf/indonesia_sumatra_northern_report.pdf
  5. FOX News. Strong Earthquake Spawns Small Tsunami in Indonesia. September 12, 2007. http://www.foxnews.com/story/0,2933,296512,00.html
  6. IFRC. Image. 2007. http://www.ifrc.org/Docs/News/07/07091302/RTR1TSOL.jpg
  7. Relief Web. Indonesia: Lessons learned in Aceh save lives in Sumatra. September 18, 2007. http://www.reliefweb.int/rw/rwb.nsf/db900sid/YSAR-776QSM?OpenDocument
  8. The New York Times. Second Powerful Quake Hits Indonesia. September 13, 2007. http://www.nytimes.com/2007/09/13/world/asia/13quake.html?_r=3&oref=slogin&oref=slogin&oref=slogin
  9. United Nations. Nias Rebuilds After Earthqauke. April 2007. http://www.un.org/webcast/pdfs/unia1072.pdf
  10. United Nations Development Programme. Wind-Up Radios Keep Tsunami-Affected Communities Informed. May 2006. http://www.undp.or.id/tsunami/view.asp?Cat=st&FileID=20060501-2
  11. United States Geological Survey. Magnitude 8.4 – Southern Sumatra, Indonesia. 2007. http://earthquake.usgs.gov/eqcenter/eqinthenews/2007/us2007hear/#summary
  12. University of Kentucky. Series of Earthquakes off the coast of Indonesia on July 17, 2006. July 18th, 2006. http://www.uky.edu/KGS/geologichazards/earthquake_0717.htm