In a shake reminiscent of 2004, a 8.6 earthquake struck 200 miles off-shore of Sumatra Wednesday.

The quake prompted residents to flee to higher ground, fearful of a replay of events that took so many lives just a few short years ago. Tsunami alerts were issued throughout the Indian Ocean region. A short time later, the populations breathed a collective sigh of relief as a Tsunami of less than 30 inches came ashore.

That elation was short lived, however, when another slightly less powerful but yet large earthquake struck in the same area two hours later. This time, an 8.2 magnitude quake struck. Another Tsunami warning was issued for the area and large segments of the region’s population were warned of a possible series of waves. That warning was soon called off as well.

This set of quakes, and the multitude of aftershocks, are quite different from the quake and Tsunami of 2004. In that disaster, the earthquake was a mega thrust, that caused the ocean floor to heave and generate a massive wave. These quakes however, moved the plates in a horizontal fashion. This type of movement is less likely to generate a Tsunami of any size.

The 2004 tsunami, caused by a giant 9.1-magnitude earthquake, killed 230,000 people in more than a dozen countries.