Investigating the Paleo-Seismic Imprint in Sumatra

Banda Aceh, TDMRC. The gigantic event on 26 December 2004 is an oppressive moment for Indonesian. In just less than 30 minutes, the great earthquake and tsunami devastated almost a half of coastal area in Aceh and North Sumatera Region. Not only shattered the building and infrastructure, the disaster also caused more than 200 thousands people died, thousands people lost their parents, children and families, and hundred thousands other lost their shelter.

Now, seven years after the tragedy, Aceh become much better although there are still many problems left behind. Aceh is awakening, trying to revive all the life-sectors those have ever buried by one of the most devastating disaster this millenium.

Are there lessons-learnt to picked from that tragedy? Sure there are. One of them is understanding the tsunami creation through Paleo-seismic investigation in Sumatera (in this case Aceh).

According to Ibnu Rusydy, M.Sc., a geologist in TDMRC, investigating the imprint of ancient-earthquake is a human-effort to predict the earthquake eventhough there is no one scientist can exactly predict it until today.

Ibnu said, in the present context, human effort toward fulfilling that aim is continued. He gave an example, past great-earthquakes are predicted to be repeated in the future. That is why, some scientists are trying to investigate past earthquake occurances those have not been recorded in history.

Practically, he further explained, if only a big earthquake occured, generally it will followed by deformation of earth surface around the quake zone. Fortunately, today, the deformation can be observed by using GPS Geodetik L1 dan L2.

Besides, it also can be observed by using coral reefs (microatoll). Microatoll is a single coral colony which commonly living and growing vertically and highly dependent on the high and low of sea water level.

By investigating the morphology of microatoll, then it can be determined when the sea water rise and receded. The rise and receded of sea water surface indicates that there are vertical deformation that caused by earthquake.

Ibnu explained, some past earthquakes have similar rupture with previous earthquakes. The lenght of the rupture can be determined from the up and down of ground surface (coral microatoll analysis) along earthquake zone.

He asserted that the Aceh-Andaman Earthquake is different from other earthquake occurances. The Aceh-Andaman Earthquake is stand-alone, which is mean that seismic gap has been long happening around west coast Aceh. Seismic gap is region which has no earthquake occurances for some period of time and has no energy released during the time. Seismic gap become a feared region because it is predicted can release big earthquake near the region. (hsp – nn)