The Jakarta Post
The Meteorology, Climatology and Geophysics Agency (BMKG) has warned residents of Lombok in West Nusa Tenggara to steer clear of damaged buildings and landslide-prone areas, because the agency has yet to rule out the possibility of another, bigger earthquake.
The head of the BMKG’s earthquake information and early tsunami warning division, Daryono, said Monday that the 6.9-magnitude earthquake that struck the island on Sunday evening could be a foreshock to a bigger mainshock.
Daryono explained that scientists distinguished between two types of earthquakes. One is where a mainshock is followed by smaller aftershocks, and the other is a “doublet” or double earthquake, where a quake is followed by a mainshock, which could be bigger.
Previously, the head of the earthquake and tsunami mitigation division at the Geological Agency, Arifin Joko Pradipto, said what happened in West Nusa Tenggara on July 29 (6.4-magnitude earthquake) and Aug. 5 (7.0-magnitude earthquake) bore the hallmarks of a double earthquake: The interval between the two quakes was not too large (only one week), the epicenters were close to each other (less than 100 kilometers) and the quakes were of similar magnitude.
Although double earthquakes are rare, Daryono of the BMKG asked Lombok residents to stay safe.
“We have yet to figure out whether the recent 6.9-magnitude quake on Aug. 19 is a mainshock or another foreshock, which could be followed by a bigger quake. Only time will tell,” Daryono told The Jakarta Post on Monday.
The BMKG has identified the Aug. 19 quake as a fresh earthquake, because it had a different epicenter from the previous two. The epicenter was about 25 km from the previous ones.
The July 29 and Aug. 5 quakes were centered in the northwestern part of Lombok, while the Aug. 19 one was on the eastern end of the island. However, both of the epicenters were situated in the same Flores back-arc thrust system and interconnected. (evi)