Funding for regional earthquake monitoring is provided to Columbia by the U. Version dated 22 March For more information, visit www. Epicenters of earthquakes occurring between and in the New York City metropolitan region. Historical earthquakes and other events prior to are plotted with "hexagons", whereas earthquakes that have occurred since — when systematic earthquake monitoring began in the region — are plotted with "circles".
The symbol size is proportional to magnitude. Butler Councilman Ray Verdonik said area residents are well aware of the frequency of earthquakes and agrees they are often difficult to discern. Won-Young Kim, director of the Lamont-Doherty Cooperative Seismographic Network, which monitors earthquakes in the Northeast, said often very shallow, the low magnitude quakes' waves cause much ground motion.
He said even though the waves don't travel very far, they can seem more intense than the magnitude suggests. To put earthquake magnitudes in perspective, experts said each year there are about , earthquakes of 2. These mild tremors are usually not felt.
There are 30, that measure between 2. About quakes worldwide are recorded between 5. The 20 or so which fall within the 7 and 7. Those that measure at 8 or greater can totally destroy communities near the epicenter and average one every five to 10 years.
Gates said he has identified most of the region's numerous faults, but has yet to name them all. Among the unnamed include the faults responsible for last year's quakes in the region. Earthquakes in this region are intraplate ones, Gates said, meaning they occur within the plates. Earthquakes of this type account for more than 90 percent of the total seismic energy released around the world. Plates are the masses of the earth's crust that slowly move, maybe as little as a few centimeters a year to as much 18 centimeters, around the globe.
Faults such as the San Andreas are interplate and occur near where two plates meet. The theory is that as plates interact with one another, they create stress within the plate. Faults occur where the crust is weak, Gates said. This second bit of uncertainty is especially troubling for some people, including some in the media who want a neat story. But what mechanisms are responsible for the formation of these apparently active auxiliary faults? One such mechanism, say scientists, is the westward pressure the Atlantic Ocean exerts on the North American Plate, which for the most part resists any movement.
That zone of weakness exacerbates the formation of auxiliary faults, and thereby the series of minor earthquakes the state has experienced over the years. All this presupposes, of course, that any intraplate stress in this area will continue to be released gradually, in a series of relatively minor earthquakes or releases of energy. But what if that were not the case?
What if the stress continued to build up, and the release of large amounts of energy came all at once? Although estimates of their magnitude have been revised downward in recent years to less than magnitude 8, these earthquakes are generally regarded as among the largest intraplate events to have occurred in the continental United States.
For a number of reasons—including the relatively low odds that the kind of stored energy that unleashed the New Madrid events could ever build up here—earthquakes of plus-6 magnitude are probably not in our future. Still, says Kim, even a magnitude 6 earthquake in certain areas of the state could do considerable damage, especially if its intensity or ground shaking was of sufficient strength.
In a state as geologically diverse and densely populated as New Jersey, this is a crucial wild card. Part of the job of the experts at the New Jersey Geological Survey is to assess the seismic hazards in different parts of the state. Two of these features relate to the tendency of soil in a given area to lose strength, liquefy, or slide downhill when shaken.
Estimates for the various counties—nine to date have been studied—are sent to the New Jersey Office of Emergency Management, which provided partial funding for the project. The amount of energy released or the magnitude of an event is clearly a big factor. In addition to magnitude, other factors that affect intensity are the distance of the observer or structure from the epicenter, where intensity is the greatest; the depth beneath the surface of the initial rupture, with shallower ruptures producing more ground shaking than deeper ones; and, most significantly, the ground geology or material that the shock wave generated by the earthquake must pass through.
As a rule, softer materials like sand and gravel shake much more intensely than harder materials, because the softer materials are comparatively inefficient energy conductors, so whatever energy is released by the quake tends to be trapped, dispersing much more slowly. In contrast, harder materials, like the solid rock found widely in the Highlands, are brittle and break under pressure, but conduct energy well, so that even big shock waves disperse much more rapidly through them, thereby weakening the amount of ground shaking.
Although the weakest soils are scattered throughout the state, including the Highlands, which besides harder rock also contains areas of glacial lakes, clays, and wetlands, they are most evident in the Piedmont and the Coastal Plain. We've received your submission.
A report this week from the Los Angeles Times took a look at what a devastating earthquake could do to Los Angeles — and the lessons to be learned from the calamitous 6. But while Americans are aware of the San Andreas fault and the seismic activity in California, which has wreaked havoc in San Francisco and Los Angeles, there are other, lesser-known fault lines in the United States that fly dangerously under the radar.
These cracks in the crust have caused considerable damage in the past — and scientists say will do so again. In , New Yorkers were jolted by a 5. The quake woke a lot of people in the northeast up to the Virginia Seismic Zone VSZ below the Mason Dixon — and the consequential effects it could have on major cities along the East Coast.
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