TEMPO.CO, Bandung - As of Sunday, September 29, at 10:00 a.m., Meteorology, Climatology, and Geophysics Agency recorded 613 aftershocks following the 6.5 magnitude earthquake in Kairatu, Ambon on Thursday, September 26.

As many as 72 of the aftershocks were felt by the community. “Based on BMKG monitoring result, the quake frequency is getting smaller, that means its activity is declining,” said the agency’s earthquake and tsunami mitigation head Daryono.

Referred to several scientific journals, Maluku has complex tectonic conditions, especially in Ambon and Seram Island. There are found many tectonic elements in the region. “They are Sorong Fault, Buru Fault, Tarera Aiduna Fault, and Seram Trough,” Daryono outlined.

The agency confirmed that the tremor in Kairatu, Haruku, Masohi, and AMbon was related to the activity of one of the faults. A scientific paper entitled "Tectonic evolution of North Seram Basin, Indonesia, and its control over hydrocarbon accumulation conditions" by Zhugang et al in 2016 served as a clue to the source of Kairatu-Ambon quake.

“There is one fault structure allegedly having a connection, namely in Kawa horizontal fault route,” Daryono added, reasoning that the quake epicenter was located right on the fault line.

The structure of the fault forms an arc that curves to the north as follows Seram Island arc pattern. The route is from the western end of Manipa Island, Seram Island, until Gorong Island in the east end. “The structure is estimated to be around 453 kilometers in length,” he said.

The series of tectonic earthquake activities in Kairatu, Haruku, Masohi, and Ambon which are still occurring are purely aftershocks. The quake was the result of tectonic forces after a terrible shift (deformation) to return to its original position or find a new stable position.

ANWAR SISWADI