Wednesday’s giant earthquake and subsequent small tsunami in Indonesia/Banda Aceh generated lunchtime talk in my office. Folks in Sweden travel quite often to Thailand these days, and the 2004 Christmas tsunami killed over 500 Swedes, of the tens of thousands killed around the Indian Ocean.
Some of my colleagues know these beaches that were at risk this week, after the 8.6 and 8.3 magnitude earthquakes. They wondered aloud, why, before the 2004 event, did no one think about devastating tsunamis? And now, after that and the Tohoku tsunami in Japan year ago, people around the world are well-aware of these natural disasters.
It’s human nature to think that because of these large events within the past few years, this must be a trend. We tend to look for patterns. But large earthquakes are relatively rare, and the earthquakes this time — though large — seemingly did not have the same power as the just-over-magnitude-9 that jerked the seafloor in 2004. (A magnitude 9 earthquake is 10 times bigger than a magnitude 8, with about 32 times the energy, because of the log scale that describes these events.) But it’s not just size — it’s the way the waves travel and where they originate, which affects the movements of the earth. The 2004 event pushed the seafloor up, creating a big wave, whereas the horizontal movement this week was different enough that it didn’t push the water in the same way, according to seismologist John McCluskey, speaking to the BBC.
Still, as McCluskey pointed out, the people who have experienced giant earthquakes before will react — and did — to evacuate and save themselves if possible, should another tsunami of equal magnitude happen any time soon. Parsing the seismological data would have taken too long to figure out which way the seafloor did move, and whether or not a big wave was on its way.
As we sat in the kitchen at work over our lunches, waiting to hear how things would unfold half a world away, we could only think with dismay of the losses that could come again, so soon after the last round. We talked about the stones in Japan that sit on hillsides there, marking the height of a past huge tsunami — a reminder not to build too close to shore in an earthquake-prone subduction zone, from long before anyone knew what a subduction zone was. One of my colleagues, who was in Thailand in January, recalled seeing all of the newly rebuilt infrastructure. Thank goodness a tsunami didn’t happen — this time.
“Tsunami, wave of the day”: I cannot remember what television show this was from, but I remember saying in a lot in junior high in the 1980s. That was long before any damaging tsunamis made the global news waves.
DART warning system, which seemed to work: http://nctr.pmel.noaa.gov/Dart/dart_pb1.html