Tsunamis are a powerful and deadly phenomenon. But they are also powerfully fascinating. By now we have all heard the reports that last Tuesday (Sept. 29) at around dawn, four 15- to 20-foot waves hit the U.S. territory of Samoa in the South Pacific Ocean, and the islands of Samoa and Tonga. The massive waves were triggered by an 8.0 magnitude earthquake that occurred about 112 miles beneath the ocean floor, about 120 miles off the coast of American Samoa. The main wave is reported to have washed at least a mile inland and USA Today has called it the worse natural disaster “on U.S. soil” since Hurricane Katrina in 2005. The following day, a separate 7.6 magnitude quake hit western Indonesia off the island of Sumatra. According to an article in USA Today, “Indonesia, a poor, sprawling nation, sits on a major geological fault zone and is frequently hit by earthquakes. The latest quakes were along the same fault line that spawned the 2004 Asian tsunami that killed 230,000 people in a dozen nations.” (Italics are added for emphasis.)
New research published in the journal Nature says that large earthquakes that happen in one part of the globe can weaken fault-strengths in other, remote areas of the planet. New Scientist calls this a “geological butterfly effect,” and rightly so given that the study’s authors say that the 2004 earthquake in Sumatra led to strength changes in the San Andreas fault in California. This long-distance cause-and-effect linkage drives home the point that we all inhabit the same small planet. (While contemplating this long-distance linkage, consider too that American Samoa is roughly equidistant between the island of Sumatra — which was hit again this week — and the San Andreas fault, which was affected in the 2004 Sumatra quake… meaning, these “distant” events could hit closer to home.)
The authors of the study in Nature argue that based on evidence from the 2004 Sumatra-Andaman earthquake,
…the very largest earthquakes may have a global influence on the strength of the Earth’s fault systems. As such a perturbation would bring many fault zones closer to failure, it should lead to temporal clustering of global seismicity.
Phrased more simply, they are saying that the really big quakes influence many different fault systems world wide. And a really big quake can possibly lead to a temporary uptick in seismic activity globally.
My fascination with the mega-movements in the earth’s crust does not lesson my sympathy to the people who endured these events though. Their suffering has been great. A BBC report I heard on the radio yesterday stated that most people who die in tsunami events die from being beaten to death by the debris that is uprooted from the earth, washed around and then sucked back to sea. Imagine that you were caught up in one of these waves, and tossed around like flotsam and mashed against floating cars, telephone poles and torn-off roofs.
One fortunate side effect of the 2004 tsunami that struck Indonesia was that more attention was given to developing an early-warning system for killer waves. Reports I’ve read state that the early-warning system did not go off early enough to save lives in Samoa this time, but it has expanded from four monitoring devices in the Indian Ocean (in 2004) to 50 today. Read this MSNBC article, “How wave warnings work,” to learn more about the early-warning system.