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<br /> <br />50 <br /> <br />III <br /> <br />Seismicity <br /> <br />Background <br /> <br />Much of Colorado Is at lofty elevations consisting of high <br />mounta i ns and i nterven i ng parks or structura I bas I ns'" A <br />generation ago most geologists thought them to be a result of <br />ancient mountain building and that the forces that created <br />them dissipated millions of years ago. Now geologists <br />recogn 1 ze that many of the state I 5 mounta t n ranges and bas i ns <br />are geologically youthful and that the faults associated with <br />them continue to move and have the potential for generating <br />earthquakes. <br /> <br />In the 120 years that modern man has occupied Colorado. <br />hundreds of earthquakes have been noted. In the early years <br />there were life I t reports." I n the I ast few decades earth <br />movements have been detected by seismographic instruments. <br />Most of the earthquakes were qu I ta sma II, but severa I <br />exceeded Richter magn J tude 5 and caused severe ground shak I ng <br />locally. A plot of known earthquakes has the same general <br />distribution as the potentially active faults. This suggests <br />that Colorado is a moderately active earthquake area and In <br />time larger earthquakes than have yet been experienced can <br />occur. Other Indications that the state has a significant <br />level of seismicity are derived from the "manmade <br />earthquakes" triggered by fluid Injections Into the earth at <br />the Rocky Mountain Arsenal near Denver and near Rangely In <br />northwestern Colorado. <br /> <br />Probably the largest quake ever felt in Colorado occurred In <br />November of 1882. It was felt throughout Colorado and In <br />several adjacent states. Accounts of the earthquake suggest <br />It was centered north of Denver near present day Broomfield <br />or Louisville. Although there were widespread but scattered <br />reports of v 101 ant ground shak i ng. re I at I ve I y II tt I e property <br />damage apparent I y resu i ted. Th i s Is probab I y due to the <br />sparseness of development and prevail tng one or two story <br />frame construction of the time. A stml lar earthquake today <br />would very possibly result In millions of dollars of property <br />damage and perhaps loss of lives. A recent study conducted <br />by the J.H. Wiggins Co., under sponsorship of the National <br />Science Foundation. shows Colorado to be third among all <br />