Extract from lohud.com news on the Indonesian earthquake.
Roger Musson, seismologist at the British geological survey who has studied Sumatra’s fault lines, says the temblor was a strike-slip quake, not a thrust quake. In a strike slip quake, the earth moves horizontally rather than vertically and doesn’t displace large volumes of water.
“When I first saw this was an 8.7 near Sumatra, I was fearing the worst,” he said, noting one of the initial reported magnitudes for the quake. “But as soon as I discovered what type of earthquake it was, then I felt a lot better.”