Indonesia quake a record, risks for Aceh grow SINGAPORE, April
13 — The powerful undersea earthquake off the Indonesian island
of Sumatra this week was a once in 2,000 years event, and
although it resulted in only a few deaths, it increases the
risks of a killer quake in the region, a leading seismologist
said. Wednesday’s 8.6 magnitude quake and a powerful aftershock
were "strike-slip" quakes and the largest of that type recorded,
Kerry Sieh, director of the Earth Observatory of Singapore, told
Reuters. “It’s a really an exceptionally large and rare event,”
he said. “Besides it being the biggest strike-slip earthquake
ever recorded, the aftershock is the second biggest as far as we
can tell,” said Sieh, who has studied the seismically active,
and deadly, fault zones around Sumatra for years. Strike-slip
quakes involve the horizontal movement of colliding earth
plates, and are typically less powerful than those where there
is vertical movement. They are also less likely to trigger big
tsunamis, or tidal waves