Tsunami week: The promise of earthquake early warning
Source: Lori Dengler
Why can’t tsunamis be treated like hurricanes? Scientists can observe the initial formation of a future hurricane far offshore, measure its development and estimate its likely course. Evacuation planning can begin days before the actual touchdown.
The problem with tsunamis is that earthquakes (their cause) can’t be predicted. It is possible to make general probability statements about earthquakes. For example, scientists studying the Cascadia subduction zone, our biggest earthquake and tsunami source, give it between a 15 percent and 30 percent likelihood of rupturing in the next 30 years. This is a strong incentive to take preparedness actions but is of no use in triggering evacuations.
Seismologists have been searching for the Holy Grail of earthquake prediction for over a century. We’ve learned a lot about the cause and mechanics of earthquakes, but as of right now there is no credible way to predict a quake in the months, weeks or days before it happens. I am completely confident in making only one predication about earthquakes — we are one day closer to our next temblor today than we were yesterday.
There is a bright spot on the horizon. Earthquake Early Warning. This is NOT earthquake prediction. Earthquake Early Warning systems analyze an earthquake AFTER it has already started, and by using extremely fast and automated algorithms, can forewarn areas further away from the epicenter seconds before the strongest shaking arrives.
Here’s how it works. Earthquakes are caused by fault rupture. That rupture produces several kinds of seismic waves. Always. The P-waves come first, speeding along at about 5 miles per second in crustal rocks. S-waves are next. They travel at about 3 miles per second, still fast but slower than P-waves. S-waves cause most of the damage in earthquakes. The Earthquake Early Warning challenge is to detect the very beginning of the earthquake in the first few seconds, make an estimate of how big the earthquake is and communicate to areas further away from the epicenter that the S-waves and their strong shaking are on their way.
All of this has to take place in seconds to be of any use. It won’t help the immediate epicentral zone where the P- and S-waves arrive at almost the same time. And at most, areas that receive the warning will only have seconds to tens of seconds to make use of this information. It requires a dense network of instruments (about 10 miles apart), an automated numerical analysis system, and robust communication networks. It also requires that we understand what it can do and how to use it.
What can you do in ten seconds to reduce earthquake impacts? It turns out quite a bit. Surgeons can stop a delicate operation, traffic onto bridges controlled, elevators brought to a floor, power stations set to a safety configuration and trains automatically slowed. Two weeks ago I was in Japan on a Bullet Train and it gave me a good feeling to know that the train was very unlikely to derail for even a very large earthquake. The Japanese have had a successful Earthquake Early Warning System for more than a decade and in the 2011 earthquake no trains outside of the tsunami zone were seriously damaged.
And what about tsunamis? Japan’s Earthquake Early Warning automated system is focused on ground shaking hazards. But researchers on both sides of the Pacific are studying how adding global positioning satellite data may improve the speed and quality of tsunami forecasts.
Earthquake Early Warning has the potential to safeguard lives and property in large earthquakes. But it won’t make buildings safer or prevent tsunamis from occurring. It can be an important component to reducing losses, but we still need to retrofit older buildings and reduce hazards within buildings. And when it comes to tsunamis — feeling an earthquake that shakes a long time is likely to be your first tsunami warning for the immediate future.
A demonstration system for West Coast states called “ShakeAlert” began in 2012, but a fully functional Earthquake Early Warning System comparable to Japan’s system will take the installation of new instruments and the upgrading of older ones and require state and federal resources. From my perspective, this is money well spent — reducing losses means a speedier recovery and a win for all of us. For more information about ShakeAlert go to pubs.usgs.gov/fs/2014/3083/pdf/fs2014-3083.pdf.
Lori Dengler is a professor in the Geology Department of Humboldt State University, an expert on tsunami education and mitigation, and the co-author of “The Extraordinary Voyage of Kamome.”
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