The September 30th and October 1st earthquakes in southern Sumatra

Figure 1. The map of Indonesia where the Sumatra earthquakes occurred. Courtesy image of: MCEER

My topic is on Sumatra, which is located in Indonesia. It is known to be one of the many islands located in Indonesia. Sumatra is one of the biggest Islands in Indonesia. This Island has many beautiful cities such as, Padang, Lumpur, Pekanbaru, Jakarta, Singapore. Sumatra is known to be a beautiful Island, but there are many earthquakes that occur in Sumatra because Indonesia sits on an earthquake fault zone(CBS News). Sumatra has been through many disasters such as; earthquakes, floods, landslides, and tsunami. The last big earthquake that happened in Sumatra was recently on September 30 and October 1st 2009.

Background information

When and where did it occur?
On Wednesday September 30, 2009 at 10:16:09 UTC and 5:16:09 pm at epicenter. There have been many other earthquakes in southern Sumatra such as in the year 2001, 2004, and 2007 (Hyndman 116). The September 30, 2009 earthquake lasted 45 seconds ( The first aftershock occurred 22 minutes after the first earthquake ( The next day, which was Thursday October 1, 2009 at 2:20:30 UTC, 9:20:30 am at epicenter the second earthquake, occurred in southern Sumatra. The second earthquake lasted 1.11 seconds(USGS).

What type of event was it?
The Type of event was a Thrust Fault and it was a 7.6 magnitude on September 30 with aftershocks of 5.5 magnitude( The depth of the September 30 earthquake was 81 kilometers. The other earthquake was a 6.6 magnitude on October 1 with depth of 10 kilometers (USGS). This earthquake occurred in Southern Sumatra, Indonesia. The cities that were affected by the September 30 earthquake were; Padang, Pekanbaru, Sigbolga, Kuala Lumpur. The other cities affected by the October 1st earthquake were; Padang, Jakarta, Singapore, Bengkulu. The type of waves this earthquake encountered were all types of waves. Starting with P waves and ending in surface waves. The surface waves are the strongest waves making the surface move up and down and side to side (Hyndman 44 ). It says in an article that the earthquake started at the sea and went to the Island (CBS NEWS). This earthquake brought a tsunami bringing landslides and floods were created (The Economist Newspaper).

Figure 2. This image is of a destroyed hotel in Padang and soldiers are rescuing people that were trapped. Courtesy image of:

What were the consequences on people/monetary?
The consequences of these two earthquakes were devastating. It destroyed the city of Padang and many people were killed. In an article it said that on September 30 many people were trapped under the buildings and that the number of incidents was to increase (Malaysian National Agency). After the first earthquake had happened many people were terrified because buildings had fallen, homes were destroyed and people were trapped under the buildings. The next day on October 1 another earthquake hit them. One after the other this was a huge shock for the people of Sumatra because they were healing from the first earthquake when the second one occurred. Many people were devastated looking for their loved ones. It is said that the people from Sumatra know that their Islands are full of earthquakes and wait for more to come that is why the people of Sumatra are trained for disaster such as these. These people know were to go when situations as these happen but unfortunately these two earthquakes did not give these people the time to save their lives and others(CBS News ). In an article it explains how the economic growth of Indonesia has been affected. The consequence as of monetary was that Sumatra financial issues went down because they did not have enough money for these tragic situations. They only had around 25 million for two months if tragic situations happened (CBS News).This earthquake was huge because it destroyed many buildings, companies, hotels, homes, and schools.

Figure 3. A building that was destroyed from the earthquake in Padang. Courtesy Image of:

The September 30th and October 1st earthquakes in southern Sumatra, discuss the two different types of faulting and the relative damage caused by these events.

There are different types of faulting in earthquakes. Faults are simply fractures in the crust along which rocks on one side of the break move past those on the other (Hyndman). The two different types of faulting in the September 30th and October 1st earthquake is an oblique fault and a thrust fault ( An oblique fault is if the slip on a fault is partly strike-slip and party dip-slip ( A thrust fault is also similar to a reverse fault, only that the thrust fault surface is more gently inclined (figure 4). In a thrust fault as in a reverse fault the rocks move on the upper side of the fault up and over those below (Hyndman 33). According to Daily KOS website the Sumatra earthquake occurred as a result of oblique-thrust faulting near the subduction plate boundary between Australian and Sunda plates ( A subduction zone is a tectonic environment in which earthquakes occur (Hyndman 39). The relative damage caused by these events was devastating. The damages that these earthquakes cause destroyed buildings, towns, hospitals, schools, homes. It brought floods, avalanches, and rain. According to an article this devastating event blocked roads and bridges. The phone and power lines were out (The Economist). Not only this event destroyed buildings, but it destroyed many families’ lives. Many people were killed during this earthquake event.

external image Thrust.gif
Figure 4. Thrust Fault

Sumatra one of the biggest Island in Indonesia has gone through many devastating events, such as in earthquakes starting in 2001 and 2007 and recently the September 30th and October 1st earthquake in 2009, which were 7.6 and 6.6 magnitude earthquake. Also having to go through aftershocks minutes after the big earthquake is devastating. This last earthquake that occurred left the Island torn into pieces. With buildings being destroyed, avalanches starting to occur, people trying to survive, but in the end being killed in seconds of this earthquake. These people of the Island of Sumatra will never forget what occurred in this event. Even though the Island of Sumatra has suffered many earthquakes and even though it will take time to heel everything that happened they have strong people who continue with their lives no matter what.

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"PADANG EARTHQUAKE: DEATH TOLL STANDS AT 75 SO FAR." BERNAMA The Malaysian National News Agency (Sept 30, 2009): NA. General Reference Center Gold.Gale.
San BernardinoCounty Library. 3 Nov.2009

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