A series of earthquakes

KOMPAS/TOTOK WIJAYANTO

Members of the National Search and Rescue Agency (Basarnas) on Monday (08/06/2018) tried to evacuate victims, who were trapped inside Jabal Nur Mosque in Lading-Lading village, Tanjung, North Lombok, West Nusa Tenggara. The mosque collapsed during an earthquake the day earlier. A number of worshipers of the mosque were trapped while conducting Isya Prayer.

Two major earthquakes that hit Lombok, West Nusa Tenggara, in the past week were connected to each other. The 7-magnitude earthquake on Sunday (5/8/2018) was the main shock while the 6.4-magnitude earthquake on July 29 was the foreshock.

The head of the Meteorology, Climatology and Geophysics Agency\'s (BMKG) earthquake and tsunami mitigation division, Daryono, explained on Monday that the two earthquakes were induced by a geological structure called the Flores thrust. The earthquakes’ deformation zone slanted southward and triggered ruptures on the bottom of the sea to Bali’s north.

The hypocenters of both earthquakes were located close to each other, thereby enabling one to induce the other. BMKG chair Dwikorita Karnawati said Sunday’s earthquake could have triggered a tsunami, despite the hypocenter being inland because the fault area elongated toward the bottom of the ocean near Lombok’s northern coast.

Researcher Mudrik Daryono at the Indonesian Institute of Sciences’ (LIPI) Center for Geotechnology Research said Sunday’s earthquake in the western Lombok segment was induced by energy propagating from the northern Lombok segment. When rocks on neighboring segments cannot withstand a transfer of energy, earthquakes may occur.

The two segments are part of a series of segments on the Bali-Nusa Tenggara back thrust or the Flores back thrust, spanning from the Madura Strait to Nusa Tenggara.

The series of earthquakes in several places on Sunday were believed to have been connected to interactions between segments in this fault area. Marine geological research in the region is necessary to understand the earthquake patterns.

“Thus far, we have been too focused on earthquakes in the south. This major earthquake in Lombok indicates threats of earthquakes in the north of Bali and Nusa Tenggara,” LIPI earthquake researcher Danny Hilman said.

Lombok was hit by a 6.1-magnitude earthquake in 1979, a 6.2-magnitude earthquake in 2004 and a 5.4-magnitude earthquake in 2013. (YUN/TAM/SEM)