October 17, 2006—The Hawaiian Islands are no strangers to earthquakes. The volcanoes that formed the archipelago are constantly growing, and magma moving underground routinely triggers minor temblors.

But the magnitude 6.7 quake that battered the Big Island on Sunday—the largest to strike the island chain in 20 years—most likely wasn't caused by this type of volcanic activity, scientists say (read news story.)

Learn more about the stresses and strains that cause earthquakes, discover why Sunday's rumbling was so unusual, and find out about Hawai'i's deadliest temblor, an 1868 disaster that kicked up a lethal tsunami.