People are evacuated from a shopping mall after a strong earthquake was felt in Medan, Sumatra island, Indonesia (AP)
Two massive earthquakes have triggered back-to-back tsunami warnings for Indonesia sending frightened people to high ground .
But they produced no deadly waves or serious damage and an alert for much of the Indian Ocean was lifted after a few hours.
Women and children cried in Aceh, where memories are still vivid of the 2004 tsunami that killed 170,000 people in the province alone. Others screamed "God is great" as they poured from their homes or searched frantically for separated family members. Patients were wheeled out of hospitals, some still lying in their beds with drips attached to their arms.
The US Geological Survey said the first 8.6-magnitude quake was a shallow 14 miles underground in the sea 270 miles from Aceh's provincial capital. An alert that followed from the Pacific Tsunami Warning Centre in Hawaii advised countries all along the rim of the Indian Ocean, from Australia and India to as far off as Africa, that a seismically charged wave could head their way.
Two deadly tsunamis in the last decade - the most recent off Japan just one year ago - have left the world much better prepared. Sirens sounded along coastlines and warnings spread like wildfire by mobile phone text messaging. Though often chaotic, evacuations began immediately with streets clogged with traffic, especially in Aceh. The only wave to hit, though, was less than 30 inches high, rolling to Indonesia's emptied coastline.
Just as the region was sighing relief, an 8.2-magnitude aftershock followed. Residents in Aceh could hardly believe it. "What did we do to deserve this?" cried Aisyah Husaini, 47, who lost both her parents and a son in the 2004 tsunami. "What sins have we committed? I'm so scared, I don't want to lose my family again," she said, clinging to her two children in a mosque in Banda Aceh, where hundreds of people sheltered.
Again, though, the threat quickly passed. Experts said the quakes did not have the potential to create massive tsunamis because the friction and shaking occurred horizontally, not vertically. The earth's tectonic plates slid against each other, creating more of a vibration in the water. In contrast, mega-thrust quakes cause the seabed to rise or drop vertically, displacing massive amounts of water and sending towering waves racing across the ocean at jetliner speeds.
The tremors were felt in neighbouring Malaysia, where high-rise buildings shook, and Thailand, India and Bangladesh. They, Sri Lanka and the Maldives evacuated buildings and beaches and readied relief efforts in case of disaster.
The World Meteorological Organisation said communication systems set up after the 2004 tsunami appeared to have worked well.
Indonesia straddles a series of fault lines that makes the vast island nation prone to volcanic and seismic activity. The giant 9.1-magnitude quake and tsunami on Boxing Day 2004 killed 230,000 people in about a dozen nations.