(CNN) With Indonesia, the question is not whether an earthquake will occur but when.
The Southeast Asian archipelago nation is reeling after yet another powerful earthquake struck Friday, followed by a tsunami, leaving nearly 400 people dead and hundreds injured. The walls of water engulfed towns, swept away buildings and tossed cars like toys.
Indonesia is prone to earthquakes because it’s on the Ring of Fire, an arc of volcanoes and fault lines in the basin of the Pacific Ocean. The area shaped like a shoe spans 40,000 kilometers (25,000 miles) and is where a majority of the world’s earthquakes occur.
One of the most seismically active zones on the planet, it stretches from Japan and Indonesia on one side of the Pacific all the way across to California and South America on the other.
“Plate tectonics and the Ring of Fire are the main reasons why Indonesia has so many earthquakes and volcanic eruptions,” CNN meteorologist Allison Chinchar said. “The earth below them is constantly changing and constantly moving.
In recent months, the Indonesian archipelago has been hammered by earthquakes, a deadly reminder of the islands’ dangerous location
Residents were still recovering from a 6.4 magnitude earthquake that struck the popular tourist island of Lombok in July when a 6.9 temblor was reported in August.
The July quake killed about 15 people, while more than 400 people died in the wake of the August 5 tremor, officials said. The latter was also felt in neighboring Bali, another popular tourist spot.
The main earthquakes are followed by dozens of aftershocks that continue for days.