Aftershocks often continue for many weeks, months or even years after larger earthquakes. Actually, there are two ways to speak about the duration of an earthquake. The above refers to the shaking perceived on the ground and is what most people are interested in. A second, more scientific definition of duration would the time it takes the underground fault to rupture along its affected surface during the quake.
It starts to break at a point and then the rupture propagates along the fault surface at a velocity of approx. This will give a much shorter value as at this speed, even distances of several km for magnitude quakes are covered in typically less than a minute. However, shaking or ground vibration lasts longer, such as waves on a water surface hit by a stone continue for some time even after the stone has sunken under the water.
There are other differences, of course — one's a transform fault where two plates are scooting past each other, the other's more of a rift type thing where North America started splitting apart, then decided to stay together — but the main thing is speed.
According to the study, San Andreas locks and loads within a decade or so, leaving the aftershocks in the dust and nervous Californians waiting for the Big One. New Madrid's still squirming around trying to get comfortable after a fairly dramatic disruption. And every time it twitches noticeably, folks in the Midwest get twitchy themselves. The river did, after all, run backwards the last time this thing went crack.
Bound to worry folks a bit. But according to Stein and Liu, there's nothing much to worry about — at least, not where New Madrid's concerned. You're just in for hundreds of years of aftershocks, since the fault moves more than times slower than the San Andreas. This is good news.
And the data are beautiful :. And this study points to the fact that the small isn't always a foreshadow of the big :. Sounds like a very good idea to me. Anything we can do to increase the chances of successful earthquake prediction could help save a lot of lives.
And it allows us to rest easier when we find out that those little temblors are just past earthquakes saying "So long, and thanks for all the fish. The views expressed are those of the author s and are not necessarily those of Scientific American. A confirmed adorer of the good science of rock-breaking, Dana Hunter explores geology with an emphasis on volcanic processes, geology news, and the intersection of science and society. Already a subscriber? Sign in.
Thanks for reading Scientific American. Create your free account or Sign in to continue. See Subscription Options. Discover World-Changing Science. Stein and Liu analyzed earthquake data gathered worldwide. For major quakes that occurred where the sides of a fault moved past each other at average rates of more than 10 millimeters per year — as the two sides of many tectonic boundaries do — aftershocks died off after a decade or so.
But for faults where the sides scraped past each other at just a few millimeters per year, aftershocks lasted about years, the researchers reported. The longest series of aftershocks, some which have lasted several centuries, were triggered by quakes that occurred in continental interiors along slow-moving faults.
Large earthquakes are often followed by aftershocks, the result of changes in the surrounding crust brought about by the initial shock. For these earthquakes very high levels of aftershocks mean that continuous ground shaking can be felt for some hours. Privacy Statement Disclaimer and Copyright. Staff Search. Earthquakes Earthquakes at a Plate Boundary. New Zealands Largest Fault. Earthquakes and Faults. New Zealand Earthquakes.
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