Quake may awaken nearby volcano

"Theoretically as well as statistically, there is a very large possibility that tectonic activities trigger or increase volcanic activities," said Syamsulrizal, who works at Indonesia's national vulcanology office.

Quake activity near a dormant volcano may "switch it on," while already active volcanoes could see more intense rumblings, said the head of the office's department for disaster risk evaluation.

Since Saturday's 6.3-magnitude earthquake, seismologists have noted increased flows of lava and heat clouds at Merapi, just north of the temblor's epicentre.