BANDA ACEH, Indonesia (AP) — Two massive earthquakes triggered back-to-back tsunami warnings for Indonesia today, sending panicked residents fleeing to high ground in cars and on the backs of motorcycles. There were no signs of deadly waves, however, or serious damage, and a watch for much of the Indian Ocean was lifted after a few hours.

Women and children were crying in Aceh province, where memories are still raw of a 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.

The U.S. Geological Survey said the first 8.6-magnitude quake was 270 miles from Aceh’s provincial capital. The tsunami watch that followed from the Pacific Tsunami Warning Center in Hawaii advised countries all along the rim of the Indian Ocean, from Australia and India to as far off as Africa, that a tsunami could be generated.

The only wave, however, was less than 30 inches high, rolling to Indonesia’s coast.

But just as the region was sighing relief, an 8.2-magnitude aftershock hit.

“We just issued another tsunami warning,” Prih Harjadi, from Indonesia’s geophysics agency, told TVOne in a live interview.

His countrymen were told to stay clear of western coasts.

Again, the threat quickly passed.

Experts said both quakes were geologically different than the one that spawned the 2004 tsunami, occurring horizontally, with the tectonic plates sliding against each other, creating more of a vibration in the water.

The other type of earthquake, a mega thrust, like the one that also hit off Japan last year, causes the seabed to heave and displaces water vertically, sending towering waves racing toward shores.

Roger Musson, seismologist at the British geological survey who has studied Sumatra’s fault lines, said initially he’d been “fearing the worst.”

“But as soon as I discovered what type of earthquake it was … I felt a lot better.”

The tremors were felt in neighboring Malaysia, where high-rise buildings shook. Singapore, Thailand, Bangladesh and India also were rattled.