Pada tahun 1962 terjadi 200 gempa di Colorado, salah satunya 5.0 pada skala Richter. Kejadian ini dikaitkan dengan pekerjaan pemboran batu cadas oleh US Army untuk membikin sumur besar sedalam 700 meter untuk membuang limbah senjata ke Rocky Mountains dekat Denver.
Kalau dugaan ini benar, apa analoginya dengan kejadian di Indian Ocean basin? Mungkinkah tsunami itu di-trigger oleh pekerjaan besar membangun Three Gorges Dam didaratan RRT? Salam, RM -------------------------------------- Science Can earthquakes be tamed? Human activity can cause quakes, but preventing them is harder Barry West / EPA via Sipa Press Can devastation such as that seen is this picture from Phuket, Thailand, be prevented? Analysis By James Oberg NBC News space analyst Special to MSNBC Updated: 7:37 p.m. ET Dec. 27, 2004 Faced with the horrendous devastation of the Indian Ocean catastrophe, it's natural to wonder if there isn't some way not just to improve warning systems, but to actually prevent such giant earthquakes in the first place. After all, in the winter officials in many mountainous areas prevent big avalanches by triggering smaller ones with explosives, even with military cannon. Threats from forest fires are reduced in some wooded regions by permitting –- or even deliberately setting -– small "controlled burns" to prevent the accumulation of dead brush that would eventually feed a conflagration. An earthquake is the ultimate result of slow, steady accumulation of tension in rock faces that gradually try to slip past each other, pulled by motions deep inside the Earth. The sheer force builds higher and higher and the rocks resist as much as they can. Suddenly, they slip past each other, releasing the energy in seismic bursts. On land, these shocks are felt as earthquakes; under the ocean, such seaquakes lead to tsunami waves that can cross oceans in hours and then build up in the shallows of a land mass into giant waves. It turns out that human engineering has already accidentally triggered earthquakes, providing some initial concepts of how a deliberate strategy of tension relief might be implemented. But geologists warn that replacing one big earthquake with a swarm of smaller ones might expose people to much higher total risks -- and that's assuming that such a proposal could surmount the legal and environmental hurdles likely to be put in its way. Accidental discoveries People have triggered natural earthquakes through a number of activities on the Earth's surface, most notably in the construction of large water reservoirs. As the weight of water accumulates in such reservoirs, lower rock layers yield to the stress and shift. A different kind of large pit was behind what is probably the best-known epsiode of human-induced earthquakes. In 1961, the Army drilled a 12,000-foot disposal well at its Rocky Mountain Arsenal in Colorado, northeast of Denver. Beginning in March 1962, waste fluids from arsenal operations were dumped down the well. Then a funny thing happened: An unusual series of earthquakes broke out in the area. By the end of 1962, there had been almost 200 earthquakes. At first they were small, but in December they damaged several buildings in nearby towns. Over the ensuing five years the quakes increased in frequency and force, and in April 1967 one measured magnitude 5.0. A connection was soon established between the waste dumping and the earthquakes, and dumping stopped. The quakes continued, however. So the following year, the Army started to withdraw fluid from the well in an effort to reduce the quakes. Sure enough, as the fluid concentration in the deep rocks dropped, the quakes slowed down. What was happening was that the fluids seemed to lubricate the rock layers that already were under tension. In that sense, the Army didn’t create the earthquakes, it just hurried them along by making it easier for the rocks to slip. Instead of one big quake at some point decades in the future, Colorado experienced a series of smaller quakes. Could this principle be applied to other more famous fault lines? In theory, deep wells could insert fluids into one segment of a fault line, while other wells at the segment’s ends would suck out fluids thus releasing the tension harmlessly. The process could continue segment by segment as the fault line was tamed, forestalling a massive earthquake sometime in the future. The flaws in the plan This theory "comes up every few years [but] ... is unfortunately fatally flawed in several ways," according to William Ellsworth, chief scientist of the U.S. Geological Survey's earthquake hazard team. "First," he said in an e-mail, "it takes 1,000 earthquakes of [magnitude] 6 to release the tectonic forces that go into a [magnitude] 8.” But since those smaller quakes are still serious, it would be better to restrict the force of induced quakes to a magnitude 4 -- which would mean inducing a million smaller earthquakes in order to avoid suffering one giant one. “Multiply that number by any reasonable estimate of what it would cost to induce one of them, and you are looking at costs far in excess of the expected losses” of the big quake, Ellsworth said. Furthermore, Ellsworth explained, “there is no guarantee that you could prevent a ‘4’ from growing into a ‘6’-- or even an ‘8’, particularly at the start of the process. So, your good intentions would have a fair chance of inducing the event you hope to avoid.” Thomas J. Ahrens, a geophysics professor at the California Institute of Technology, agreed with Ellsworth’s warning. Like "Jurassic Park's dinosaurs," he said, such earthquakes "may easily get out of control.” The idea of deliberate human intervention to prevent big earthquakes is a favorite one of geology enthusiasts on various Internet forums. The webmaster of one of them, http://www.earthwaves.org, noted another problem with such an endeavor: "'Triggering' implies knowledge of the stressed faults, and I'm told we keep discovering new bad ones only when they go off.” The hazard, which other posters agreed on, was that “trying to manipulate a known one seems like it has a serious chance of triggering an unknown one.” Another big problem to overcome is legal, not scientific. In a 1994 article for the Journal of Environmental Law and Litigation, authors Darlene A. Cypser and Scott D. Davis note that damage from human-induced earthquakes "cannot be excused as an act of God." Thus, liability claims could be pursued based on a number of legal precedents, including tresspass and nuisance law. Perhaps a hundred years from now, geophysics will have mapped the faults in Earth’s crust and geological engineers will have installed lubrication wells to modulate the tectonic-induced slippage so as to reduce sudden, large shocks. Until then, hurdles both scientific, technological and litigious all stand in the way. NBC News space analyst Jim Oberg is working on a book about deliberate climatic and environmental manipulation. = MSNBC Interactive ------------------------ Yahoo! Groups Sponsor --------------------~--> $4.98 domain names from Yahoo!. Register anything. http://us.click.yahoo.com/Q7_YsB/neXJAA/yQLSAA/BRUplB/TM --------------------------------------------------------------------~-> *************************************************************************** Berdikusi dg Santun & Elegan, dg Semangat Persahabatan. 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