However, the two terms are quite different, and they are often confused. Intensity is based on the observed effects of ground shaking on people, buildings, and natural features.
It varies from place to place within the disturbed region depending on the In the early s, the emergence of the theory of plate tectonics started a revolution in the earth sciences. Since then, scientists have verified and refined this theory, and now have a much better understanding of how our planet has been shaped by plate-tectonic processes. We now know that, directly or indirectly, plate tectonics A magnitude 7. Visit the USGS event page to learn more about this earthquake.
Geological Survey seismologists. Both studies shed light on more than a decade of debate on the origin and prevalence of remotely triggered earthquakes. The frequency of events will diminish with time, but damaging earthquakes will remain a threat. A minor aftershock struck the Seattle area early Thursday morning, March 1, The aftershock, which struck at a.
When is a badly damaged, but stable building safe to enter after an earthquake? That is a question that safety-response and building-department officials have to answer in order to let occupants retrieve important possessions and business records, and to let contractors begin emergency repairs. A magnitude 5. EDT a. Geological Survey. The blue dot is the location of the main Jan 23 earthquake.
Yellow and orange dots are aftershock epicenters. The aftershock sequence of the magnitude 7 earthquake that struck Haiti on Jan. Skip to main content. Search Search. Natural Hazards. Apply Filter. What is the difference between aftershocks and swarms? Aftershocks are a sequence of earthquakes that happen after a larger mainshock on a fault.
Aftershocks become less frequent with time, although they can continue for days, weeks, months, or even Do earthquakes occur in Antarctica? Earthquakes do occur in Antarctica, but not very often. The reasons why Cascadia aftershock production is so low compared to global rates are still unclear, but "one strong possibility would seem to be that temperature for the deeper slab earthquakes is a dominant controlling parameter," said Bodin, noting that "the young, hot Juan de Fuca plate is being jammed beneath North America" in Cascadia.
The deeper the earthquake, the higher the temperatures, and the researchers did find that aftershock productivity decreases with depth, Bodin explained. Methods that help researchers detect and locate smaller earthquakes could provide a better sense of overall aftershock rates and the physical processes that control them, they suggested.
Journal Bulletin of the Seismological Society of America. Before the snap, you push your fingers together and sideways. Because you are pushing them together, friction keeps them from moving to the side. When you push sideways hard enough to overcome this friction, your fingers move suddenly, releasing energy in the form of sound waves that set the air vibrating and travel from your hand to your ear, where you hear the snap. The same process goes on in an earthquake. Stresses in the earth's outer layer push the sides of the fault together.
The friction across the surface of the fault holds the rocks together so they do not slip immediately when pushed sideways.
Eventually enough stress builds up and the rocks slip suddenly, releasing energy in waves that travel through the rock to cause the shaking that we feel during an earthquake. Just as you snap your fingers with the whole area of your fingertip and thumb, earthquakes happen over an area of the fault, called the rupture surface.
However, unlike your fingers, the whole fault plane does not slip at once. The rupture begins at a point on the fault plane called the hypocenter, a point usually deep down on the fault. The epicenter is the point on the surface directly above the hypocenter. The rupture keeps spreading until something stops it exactly how this happens is a hot research topic in seismology.
Part of living with earthquakes is living with aftershocks. Earthquakes come in clusters. In any earthquake cluster, the largest one is called the mainshock; anything before it is a foreshock, and anything after it is an aftershock. Aftershocks are earthquakes that usually occur near the mainshock. Go ahead.
Search for photos of "New Madrid Fault. Lots of maps, not many photos, right? That's because not a lot's going on there.
Most of it's concealed below the surface, and what's been exposed doesn't look much like a fault. Unless you're a professional, the photo of the fault at this Missouri Department of Natural Resources article doesn't exactly stand out. Ed Yong says ,. In other words, there's not a lot going on that would show at the surface, unlike the San Andreas, which is bleeding obvious.
New Madrid is a slow, sleepy fault, despite the excitement it caused over the winter of Compared to New Madrid, the San Andreas fault is a speed demon, and it shows. 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 :.
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