August 30, 2011

East Coast Earthquake Recorded at Snee Hall

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Easily unnoticed amid of the excitement for a new academic year, a 5.8 magnitude earthquake shook the Cornell campus and much of the East Coast on Aug. 23 around 2p.m. The vibrations were recorded by the University’s seismograph, and the results, which are still in the process of being analyzed, are now up on display in the lobby of Snee Hall.According to the U.S. Geological Survey, an earthquake occurs when two blocks of the Earth suddenly slip past one another along a surface called a fault or fault plane. Since the earth is made up of tectonic plates that move very slowly beneath the surface, the rough edges — called plate boundaries — often get stuck while the rest of the plate keeps moving. When the plate moves far enough, the edges separate on one of the faults and an earthquake occurs.

Earthquakes along the East Coast of the United States are therefore very rare, since the area is not located on a known fault line. According to Prof. Larry Brown, earth and atmospheric sciences, their rarity also makes them difficult to understand. “It’s hard to deal with them as a threat because they are so unpredictable and rare,” he said.The Aug. 23 earthquake, which originated in Virginia, is distinct primarily because it is quite large for the area. “I think it may be the largest one to have occurred in the Virginia area,” Brown told Gothamist. “The fact that it occurred near Washington, D.C., gets some people’s attention. And the fact that it did not occur in California makes it one of those mysterious earthquakes that don’t occur according to the simple tenets of plate tectonics, so it’s quite an interesting event,” he said. Most earthquakes of this magnitude typically have aftershocks, Brown explained, but they may be too small to feel and notice. “They could typically be up to one magnitude unit smaller than the main event, which is a factor of 10, so that’s quite a bit smaller,” he said. Many people didn’t even feel the earthquake itself, let alone its aftershocks. “I didn’t feel it at all,” said Kendra Bartell ‘12. “I just saw on Facebook and Twitter that we had one.”Others, however, felt the ground move beneath their feet. “I had to grab on to something because I felt dizzy and everything was shaking,” said Irina Starkova ’13. In addition to the geological aspect of an earthquake, there is a significant psychological impact as well, Brown said. “It’s very unnerving to find yourself no longer on stable ground, especially if you are on an upper floor building, because the building’s response will be a function of the structure of the building,” he said. “It tends to be a fact that higher floors move further than lower floors, and frankly you get motion sickness. I think a lot of it’s psychological. You’re walking and suddenly the ground you expect to be stable is no longer stable. It can be very disconcerting.”Because of the proximity in time to the Aug 22nd 5.3 earthquake in Colorado, some believed the two to be linked, but Brown explained that a connection is improbable. “There is certainly a lot of interest in remote trigger of earthquakes. Generally they relate to really big earthquakes and areas that are very tectonically active,” he said. “He could conceive of some fairly unlikely series of events in which an earthquake could trigger, but it would be extremely unlikely.”Whatever the cause of the Virginia-based quake, it has provided a unique opportunity for scientists to examine the event using modern analysis techniques, such as piecing together information from many seismographs like the one in Snee Hall.  A seismograph is an instrument that records the details of earthquakes, such as force and duration, as measured by several seismometers, all located in a seismic vault also in Snee. The seismograph uses three colors to illustrate the motion of the ground during an earthquake: blue, red and green. The blue represents the up-and-down movement of the ground below Snee, the red is east and west and the green is north and south. The record that the instrument captured is now on display in Snee Hall’s lobby and is, according to Brown, “beautiful.”

Original Author: Maria Minsker