TEMPO.CO, Jakarta – There are two anomalies in the earthquake that rocked Lombok, West Nusa Tenggara, on Sunday, August 5. First, the quake's epicenter is located on land, yet it could trigger a tsunami. Second, the quake is known as a doublet earthquake, but it had unique characteristics compared to previous quakes.
The head of earthquake and tsunami mitigation of the Volcanology and Geological Disaster Migitation Center (PVMBG), M. Arifin Joko Pradipto, has commented on the tsunami.
“How could it trigger a tsunami even though it came from land? It is suspected that a tsunami occured because the crack line continued to the seabed,” said Arifin today.
Earlier, the Meteorology, Climatology and Geophysics Agency (BMKG) released an early tsunami warning following the magnitude 7 earthquake in Lombok. The agency recorded a 0.135-meter tsunami in Carik and 0.1-meter tsunami in Badasr.
“The crack line reached the ocean, which caused a tsunami, despite being a minor one,” said Arifin.
According to Arifin, the quake’s epicenter originated from the Flores Back Arc Thrust that extends to North Lombok’s waters, Sumbawa, up to Flores. The fault’s mechanism arose from south to north, while the fault from the north smashed the earth under the islands.
He explained that the quake in July 29 and the Lombok quake on August 5 might originate from the same fault line.
“The BMKG said that the August 5 quake was a main shock, but it is debatable since the two quakes could be a doublet earthquake,” Arifin said. He said that the quakes met the requirements of a doublet, which is within a 10 kilometer radius and embodies similar strength. “It is possibly a doublet but further research is necessary to prove it.”