Indonesia Earthquake 2012

Five people died from heart attacks, and a few others were injured as mobs used cars and motorcycles to flee to high ground in Indonesia's westernmost province of Aceh – closest to the epicenters. But aside from cracks in the walls of houses and structural damage to one bridge, you would hardly know anything happened, said Usman Basyah, smiling as he handed change to customers at his small street stall.

The first quake, measuring 8.6, triggered a tsunami watch in more than two dozen nations and island territories, from Australia and India to as far off as Africa. Hours later, a powerful 8.2-magnitude aftershock hit. Indian Ocean nations acted quickly. In southern India, police, including some on horseback, spread out across Chennai's popular Marina Beach to enforce an evacuation. Sri Lankan tsunami alert teams on motorcycles drove along the coast near the capital, urging people to move to higher ground.

"It wouldn't have been as bad," said Iskandar, a local disaster management official. "But I dare to say, if there had a been a repeat, there would have been deaths." The real luck came with the type of quake that hit. Indonesia, a sprawling archipelagic nation of 240 million people, straddles a series of fault lines that makes it one of the most seismically active places on the planet. Aceh, which sits off a subduction zone fault, were one tectonic plate of the Earth's crust dives under another, has experienced numerous mega-thrust quakes over time. It's these temblors that cause the seabed to rise or drop vertically, displacing massive amounts of water that race across the ocean at jetliner speeds. But experts say Wednesday's twin tremors occurred on what is known as a strike-slip fault. The sea floor shifted horizontally, creating more of a vibration in the water.