No tsunami? Why earthquake spared Indonesia

National Geographic : An 8.6-magnitude earthquake and its 8.2-magnitude aftershock occurred off the Indonesian coast on 11 April. A tsunami alert was issued for most of the Indian Ocean, including Aceh Province, Indonesia, where 170â000 people died as a result of the December 2004 tsunami. That tsunami had waves of twenty four meters tall when it came ashore in Aceh and grew to thirty meters in some spots as it traveled further inland. Wednesday’s quake, however, led to a tsunami with waves of slightly less than one meterâmdash;high enough to notice, but not to cause any significant damage. The lesser magnitude of the more recent temblor and its different character are the reason for the difference; the more recent quake was a strike-slip event, rather than an upthrust quake. Strike-slip quakes involve tectonic plates sliding past one another horizontally rather than vertically and there was no vertical rise of the seabed to displace a large volume of water.