Experts at Germany's Potsdam-based Geo Research Center (GFZ), which is developing a tsunami early warning system for Indonesia, have warned that Southeast Asia is threatened by further aftershocks following Monday's earthquake off Indonesia's northwest coast. Earthquake expert Jochen Zschau of the GFZ told news agency dpa on Tuesday that in light of the catastrophic tsunami in December, the entire region would continue to be quake-prone for the next one to two years though the danger of serious aftershocks would lessen with time. Zschau however said that the timing of Monday's quake was surprising. "The big aftershocks usually occur immediately after the main quake," he said, adding that Monday's quake measuring 8.7 on the Richter scale "is a bit unusual." At the same time Zschau said that work on putting together a tsunami early warning system for Indonesia was underway at full steam and added that he hoped the first warning stations could be set up by the end of this year.