Before the earthquake occurred, he and several ITB lecturers conducted a research in the same area in 2016. From the result, potential earthquake sources are found in northern part of Flores with magnitude of 7.4. Looking at that potency, he thinks that the earthquake occurred last week is the mainshock of earthquake sequence that occurred before.

As already known, an earthquake also previously occurred with a magnitude of 6.4 in the same area on 29th July. According to Irwan, both earthquakes did not occur in the same spot, but came from the same source in Flores Fault.

Irwan explained that theoretically, two earthquakes with big magnitude occurring in close proximity are uncommon. Those two earthquakes are usually called doublet earthquake or earthquake that is triggered by another earthquake. “Doublet earthquake is an earthquake that releases energy and the energy is then increases the occurrence of earthquakes in adjacent places, it is not something we can easily understand,” He said in a live report with Metro TV at Aula Barat ITB.

He said that an important lesson emerges from Lombok Earthquake. After the mainshock, people have to prepare for the potency of aftershocks or even bigger shock. “When we first heard about the earthquake in Lombok, we were surprised. Scientifically the earthquake potency there is above 7.0 degrees on RMS,” he said.

Remain Vigilant
Theoretically, even though the 7.0 degrees Earthquake is the mainshock, the surrounding community must remain vigilant of the possibility of aftershocks. Adding to that, the buildings are already cracked and occurrence of 5.0 degree earthquake can cause damage. “We are worried that the buildings cracked by the mainshock can receive great impact even from small earthquake. We hope that the people of Lombok to remain strong and vigilant,” he said.

When asked if there is a guarantee that no bigger earthquake will occur, Irwan cannot guarantee it. But, what must be considered is the potency for earthquake that occur in segments adjacent to Lombok, for example Bali and to the east. It can also affect Lombok. “When asked if there is a guarantee, there is no guarantee. But, scientifically, the main energy has been released,” he said.

The next concern is the potency of volcanic activity since the location is close to Mount Agung in Bali and Mount Rinjani as two active mountains. “In Indonesia, we have a lot of research evidence of tectonic activity triggering volcanic activity. For example, the increasing activity of Mount Talang, Merapi, and Sinabung happened after tectonic earthquake. This is our homework to look in detail at Mount Rinjani and Mount Agung. Our eyes must remain vigilant to understand the potency of increasing activity in those mounts,” he explained.

BMKG reported that Lombok Earthquake that occurred on 5th August 2018 at 18:46:35 WIB as the mainshock. The source is located at -8.37 latitude and 116.48 longitude with magnitude of 7.0 with a depth of 15 kilometers. The location is 18 kilometers to the northwest of East Lombok, Nusa Tenggara Barat.

The source of Lombok Earthquake was close to a 6.4 degree earthquake that occur a week earlier on Sunday, 29th July 2018 at 05:47:39 WIB at -8.26 latitude and 116.55 longitude with a depth of 10 kilometers. The location is 28 kilometers to the northwest of East Lombok, Nusa Tenggara Barat.