Earthquake Occurances is Increasing in Sumatera

Banda Aceh, TDMRC. The earth surface is made up of a series of large plate and fault. This cause Indonesia prone to disasters, particularly earthquake. Soil types also affecting the destructive power of an earthquake. They are inseparable and always in contact to each other. From time to time, even from billion years ago. The harmony is on their hand. The earth’s surface will shatter once their friction raise-up and cause fractures.

Thus revealed by Ibnu Rusydy, M.Sc., a geologist of TDMRC, in Banda Aceh, at Zona Dipasena (Dialog Pagi Seputar Kebencanaan – a morning dialogue about disaster) that broadcasted by Djati FM 103.6 Radio, Thursday (12/4).

According to him, the Indo-Australian Fault unfold along southern to eastern part and huddled with Eurasian Plate in northern part. Indo-Australian Plate also huddled with Pacific Plate in Papua Island and Eurasian Plate collide with Pacific Plate in northern Halmahera. They are three of eight main faults of the earth.

He added, Indo-Australian and Pacific Plate are types of flexible plate while Eurasian Plate is type of rigid plate. The flexibility make Indo-Australian and Pacific Plate become much more aggressive than Eurasian Plate. Both of them are pushed and pierced into the bottom of Eurasian Plate or in geological term it called subduction. The friction between the plates going on without a pause. The friction predicted is about 3 to 7 centimeter per year. Energy will released once the strain reached its peak and a tectonic earthquake resulted.

Throughout the history, Ibnu said, the Aceh earthquake on 26 December 2004 is one of the most gigantic earthquake with the scale of 9.2 SR. The released energy is equivalent to 32 gygaton of a dynamite or equivalent US energy consumption for one year.
Because of the epicenter was in the ocean, the destructive of Aceh Earthquake became more terrible because of tsunami hit. The giant wave not only destroyed Aceh and Nias, but also swept away the life along the coast of Malaysia, Thailand, Sri Lanka, India, and East Africa. No less than 300 thousands people died.

Still in the same year, a big earthquake also attacked Alor, Nusa Tenggara Barat, on 12 October, and Nabire, Papua, on 6 February. The 7.5 and 7 SR earthquakes caused 33 people died in each regions. Previously, a big earthquake also occured in Mangole, South Maluku, with the scale of 8.3 SR. The newest occurance was in north Jayapura, last Tuesday, with the scale of 5.6 SR. Those all are caused by friction amongst the plates. How about the earthquake that caused by fault or ground fracture?

If the plate is located in sea at the depth of 600 kilometers, then the fault is located in land at the depth of less then 20 kilometers. There are two types of fault; active fault which continuous on saving friction enery and passive fault.

If we look at the fault map published by Vulcanology and Geological Hazard Mitigation Center (PVMBG), the existence of fault is like scratch out all islands in Indonesia. The fault can be turn into earthquake if both flank is rub against each other.

How About the 11 April 2012 Earthquake?
When the people still in trauma because of earthquakes in some region in Indonesia, last Wednesday (11/4/2012), at at 03.38 PM, the people in Sumatera, especially Aceh, Bengkulu, Lampung and North Sumatera was shocked by 8.6 SR earthquake at the depth of 10 kilometers  and located in 2.31 North Latitude (NL) and 92.67 East Longitude (EL). The earthquake was the third strongest earthquake that ever occured in Indonesia.

The aftershocks post giant earthquake 8.6 SR, Wednesday (11/04). (source: USGS)

According to Ibnu, if we observe from the earthquake mechanism and epicenter, the Wednesday earthquake was similar to the midnight earthquake in 11 January 2012. The earthquake did not occur in the subduction zone but in the IFZ (Investigation Fracture Zone) in Indo-Australian Plate. The earthquake triggered by the movement of strike-slip fault in Indo-Australian Fault. Commonly, earthquake in IFZ rarely cause tsunami because of at strike-slip fault rarely occured vertical dislocation in ocean floor. (hsp-nn)