Two more teams of experts have been sent to probe the mysterious blasts being heard in the Saurashtra region of Gujarat for over a month now.
Though no one has been injured, the blasts have caused slight structural damage to buildings in certain areas of Rajkot and Jamnagar.
Earlier, another team, using various monitoring instruments, had failed to establish the cause of the blasts, official sources said in Ahmedabad on Sunday.
The new teams would study earth movements in different parts of the region and set up seismographs in Surendranagar
and Jamnagar districts to get to the bottom of this mystery, the sources added.
A devastating earthquake that rocked parts of Gujarat on this day in 2001 had left several thousand dead and injured, and flattening many big and small villages.