The mechanism of the earthquake in Yogyakarta Indonesia in 2006 using GPS

YOGYAKARTA EARTHQUAKE May 27, 2006

On May 27, 2006, an earthquake in the vicinity of Yogyakarta. The quake occurred in the morning precisely at 5:53:58 pm. The epicenter is located at 7.962 ° S and 110.458 ° east, about 20 miles southwest of Jogjakarta or 455 km southeast of Jakarta with a fairly shallow depth of 10 kilometers. An earthquake measuring 6.3 Mw. Strength of an earthquake that was quite this strong, then the occurrence of the land (inland) result in damage to buildings, buildings and other infrastructure are quite severe in Yogyakarta, Bantul, and surrounding areas, as well as quite a lot of casualties.



According to the survey notes, more than 6000 people died, and about 50,000 thousand people were injured. Meanwhile, 86,000 homes were destroyed and approximately as many as 283,000 homes were damaged with each level of heavy damage, moderate, and mild. The most severe damage to buildings there are around Bantul, Imogiri, Piyungan, and Klaten. Earthquake occurrence is classified as a national disaster, and provide a series of disasters in the country notes dark Indonesia, after the disaster of earthquake and tsunami in Aceh Darussalam Nangro earth, Nias, and elsewhere.

Sufficient number of casualties and material loss showed weak earthquake monitoring system in our country. And since the occurrence of the earthquake that accompanied the tsunami in Aceh Nangro 2004, the government has launched efforts to natural disaster early warning systems earthquake and tsunami. Maybe we still need time to continue to assess, prepare, and begin actively monitoring program and mitigation of natural disasters, especially earthquakes and tsunamis.



Annals of seismicity in Jogjakarta and surrounding area

Actually if we look at historical records, it has happened several times the earthquake in Yogyakarta and surrounding areas with considerable destructive power. In 1867 an earthquake that gives the record fatalities and injuries are quite a lot, and leaving damage to buildings and infrastructure in areas which are quite extensive. In 1943 another earthquake occurred causing loss of life as much as 213 people (31 deaths in Jogjakarta), 2800 houses were destroyed, and the area experiencing the most severe damage is Kebumen and Purworejo. In 1981 an earthquake occurred back in Yogyakarta and the surrounding area, although not to cause casualties and severe damage to buildings.

If we look closely the historical record, then if we look at the mechanisms that are repeated earthquakes (earthquake cycle), then it is not possible we can work with a good mitigation, trying to minimize the impact of the loss can be caused by the earthquake. Activities "willing umbrella before it rains" may be realized with support of the research, application of technology, community empowerment, and others.



Research and application of technology in the face of catastrophic earthquakes

Earthquakes can not be prevented his arrival. What we can do is find ways to reduce losses or disasters that can be caused by earthquakes. The trick is how to implement monitoring and mitigation of potential earthquake as good as possible.

One effort that can be done in the framework of monitoring and mitigation of potential earthquake that is through research and analysis of the mechanisms and stages of the earthquake cycle. Cycle earthquake (earthquake cycle) is defined as the repetition of the earthquake. One cycle of earthquakes is usually held within a period of tens to hundreds of years. In a single cycle of earthquakes, there are several stages of earthquake mechanisms, among which interseismic stage, pre-seismic, co-seismic and post-seismic [Mori (2004), Vigny (2004), Ando (2005), Natawidjaja (2004) ]

Form of an earthquake cycle analysis done by examining historical documents earthquake occurrence, and studies of geology, geophysics such as stratigraphy of rocks, coral reefs (coral microattols) and paleo-tsunami to earthquakes that occurred at sea, paleo-likuifaksi, and so on another. Meanwhile, an earthquake of the stages of analysis done by looking at and researching the phenomena that accompany the stages of earthquakes such as deformation, seismisitas, information geophysical measurements (reseistivitas eclectic, observation of the face and ground water temperature), and others. [Mori (2004), Vigny (2004; 2005), Ando (2005), Natawidjaja (2004)].



Research Activities Yogyakarta earthquake mechanism by KK Geodesy and Counterpart

In an effort to move the learning and materials handling in the future earthquake potential, especially in Yogyakarta and surrounding areas, it is necessary to do research mechanism Yogyakarta earthquake that occurred on 27 May 2006. To see the mechanism of the Yogyakarta earthquake in 2006 can be done by finding evidence of faults (surface rupture) in the field, see the deformation coseismik poseismik by leveraging technology and Global Positioning System (GPS), monitoring with microseismometer Aftershock, and others.

In early June (about a week after the earthquake in Yogyakarta), ITB (including KK Geodesy) in collaboration with Nagoya University, Gadjah Mada University (UGM) and BPPT conduct research cooperation mechanisms earthquake in Jogjakarta. The field work carried out for approximately 10 days with other activities such as monitoring points are used to benchmark built by the BPN with a GPS to see coseismik deformation, then install the tool to see the distribution microseismik Aftershock, and others. Research activities are also accompanied by a humanitarian aid for disaster victims.

In the form of points in greater details the research activities carried out are as follows:

1) Survey damage to buildings (damage assessment) and casualties
2) Search for evidence of fracture on the surface (surface rupture)
3) Observations of GPS points BPN and other points to see the effect coseismik
4) Installation of microseismic to see the distribution of Aftershock
5) Assist disaster relief funds

Below is a picture documentation of the installation of GPS equipment at points of BPN to see coseismik see the effect of deformation resulting from the earthquake that occurred in Yogyakarta


The figure below shows the documentation of other activities in addition to research activities, namely aid for disaster victims. A grant obtained from the academic civitas ITB, then the people who provide post disaster assistance through the ITB.




Data processing and analysis of research results

From the results of field surveys of damage (damage assestment) seen considerable damage around the opaque fault corridor (from Bantul to Klaten). Mw 6.3 magnitude quake just really is not too large for the size of the quake, but it gives a fairly severe impact damage. From here arises the question of whether the condition of sedimentation layer plays an important role? Is the condition of the building plays an important role? Is the effect of the Killer Waves? Is there more than one earthquake? These things are very interesting to study further, by integrating various existing data.

From the results of field surveys to find the fault surface (surface rupture) was not obtained evidence of surface fault rupture around Opak. This gives the question of whether the earthquake did not cause surface rupture? or location of the earthquake was not occurred in the fault Opak? maybe in another fault? The answer can be obtained among others by looking at the pattern and distribution of deformation coseismik Aftershock.

From the results of GPS data processing using the Bernese software 4.2 and the documentation obtained coordinates BPN coseismic deformation with varying magnitude, but not more than 15 centimeters. Deformation pattern of systematic enough to show the mechanism of Yogyakarta earthquake in 2006 are left lateral. Furthermore, modeling results show a dip coseismic slip angle of the left lateral fault system at 50 degrees. Coseismic deformation of the results also showed that the fault rupture occurred on the east fault Opak.

Aftershock distribution of the results processed by the Nagoya University (Irwan et. Al, 2006), from 6 seismometers installed, shows the distribution of which is concentrated around the mountain ridge south fault, not disesar Opak. Fault geometry does not exceed 20 kilometers, this is in accordance with the calculation power of earthquakes, ground deformation and value. Aftershock distribution of these results reinforce the results of the analysis of GPS that shows the pattern of earthquake mechanisms Jogja 2006 is left lateral and the fault rupture occurred on the east fault Opak.

Although it looks useless to do research when disasters have occurred, but if we look at that we can still take a lesson from the disaster, for we are better in dealing with disasters in the future. One example of the results showed the actual strength of the quake was not so strong for the size of the earthquake theory, but probably because existing buildings are not designed to withstand earthquakes, and soil type so that the added effect of the damage, so for the foreseeable future we should think about how make the building completely, and others. From modeling coseismic we can know which areas are the source of the earthquake, so that we can recognize the level of seismic hazard areas, how the pattern of energy accumulation, and others.

Posted in: EARTHQUAKE,GPS