(Photo source: NY Times Dot Earth blog)
Like you, we have been watching the aftermath of the March 11, 2011, Japanese Sendai earthquake with horrified fascination. The before-and-after photos are truly sobering:
The bravery and resilience of the Japanese people are inspiring, and thankfully help is beginning to arrive, including assistance from the U.S. military. The death toll, apparently thousands or more, is heartbreaking. But that number is not grossly higher because of the success of the Japanese people, and NOAA and others, in wisely using science and engineering to prepare for the inevitable.
The most deadly known earthquake killed more than 800,000 people (most destructive earthquakes ), and many earthquakes much smaller than the March 11 Sendai event had much higher death tolls. The damaging effects of earthquakes depend on where, when and how the quake hits, as well as on the size. But it is already clear that a far greater disaster was avoided by Japan’s investment in previous decades in preparing for an event such as this one.
The cause of the earthquake is well understood. The sea floor of the Pacific Ocean is diving beneath Japan, sinking into the mantle at a subduction zone. In some places, faults between moving rocks are lubricated by ground-up rock, soft minerals and water, but in other places, such as near Sendai, the moving rocks get stuck across the fault. The rocks then bend elastically, storing energy
like great springs, until the fault breaks in an earthquake. This shakes surrounding rocks, as well as the buildings and roads and trains on them. The sudden motion of the sea floor in an earthquake moves the water above it, pushing a tsunami that races across the ocean, and eventually around the world. Long and low in deep water, the tsunami piles up as it is slowed by shallower water, causing great destruction on some shores.
Scientists have long looked for ways to predict earthquakes. The Sendai quake was preceded by many smaller events, or “foreshocks.” However, some big quakes occur without foreshocks, and sometimes a cluster of smaller quakes occurs without triggering a bigger one. So, thus far, we lack the ability to reliably forecast a big quake. (Scientists worldwide are working very hard to accurately identify warnings, including the study of glaciers and ice streams that generate “icequakes” as they move. We are hopeful that discoveries will follow.)
We do know a lot about where big quakes occur. By understanding the geology, measuring the motion of the plates, poring over written histories and reading the geologic traces of former quakes, we can learn a lot about where, when, how often and how big quakes have been. We can then use building codes to prepare for what is likely to occur, by matching investments in earthquake preparedness to the danger of earthquakes.
Furthermore, the seismic waves and tsunami waves that cause damage move slower than modern telecommunications. Thus, a widespread sensor network can detect an earthquake and warn surrounding regions. In the Sendai event, Tokyo had over a minute of warning (see Talbot, D., March 12, 2011, 80 Seconds of Warning for Tokyo, Technology Review, published by MIT, http://www.technologyreview.com/computing/35090/?p1=A3) - enough time to slow trains to avoid jumping off suddenly wiggling tracks; to allow a surgeon to quit operating; to close off gas transmission lines; and to otherwise take actions to minimize damage. The quake occurred so close to Japan that the tsunami hit some Japanese coasts only a few minutes after the first warning, but alarms raced across the Pacific well in advance of the big wave (see NOAA’s Pacific Tsunami Warning Center at http://ptwc.weather.gov), allowing responses that minimized deaths and damages.
There are immense challenges ahead for Japan, including the tasks of stabilizing and cleaning up damaged nuclear plants. The destruction is truly horrific. But the Japanese people and their neighbors around the Pacific, including the U.S., have made use of good science and engineering to avoid something far, far worse.
Note the link to the Earthquake Summary Poster and “Additional Info,” including NOAA’s video of the tsunami: http://tinyurl.com/469n4bj
There are also great resources available at the website of the Incorporated Research Institutions for Seismology, a university consortium sponsored by the National Science Foundation: http://www.iris.edu/hq/retm
For thought-provoking discussion, see Andy Revkin’s coverage for the New York Times: