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History of Dam Failures in Orange County <br /> There is no recorded history of significant dam failures occurring in Orange County, <br /> including the Town of Carrboro and Town of Hillsborough. However, several years ago, a <br /> dam breach in Chatham County,which is located directly south of Orange County,caused <br /> some flooding problems within the southern limits of the Town of Carrboro. ' <br /> Earthquake <br /> Earthquakes are geological events that involve movement or shaking of the crust of the <br /> earth. Earthquakes are measured in terms of their magnitude and intensity as shown in the <br /> table below. Earthquakes can cause devastating destruction to the manmade environment. <br /> Earthquakes are relatively infrequent but not uncommon in North Carolina. From 1568 to <br /> 1992, 157 earthquakes have occurred in North Carolina. There is no existing data to <br /> indicate that any earthquakes have occurred in Orange County. <br /> North Carolina's vulnerability to earthquakes decreases from west to east in relation to the <br /> Eastern Tennessee Seismic Zone. Epicenters are generally concentrated in this active <br /> seismic zone, which is second in activity in the eastern United States only to the New York <br /> Madrid Fault. <br /> Modified Mercalli Scale of Earthquake Intensity <br /> Maximum g�chter <br /> Scale Intensity Description of Effects Acceleration Scale <br /> (mm/sec) <br /> I Instrumental Detected onl on seismo a hs <10 <br /> II Feeble Some eo le feel it <25 <4.2 <br /> III Sli ht Felt b eo le restin ;like a truck rumblin <50 <br /> N Moderate Felt b eo le walkin <100 <br /> V Sli htl Stron Slee ers awake;church bells rin <250 <4.8 <br /> VI Strong Trees sway;suspended objects swing,objects <500 <5.4 <br /> fall off shelves <br /> VII Ve Stron Mild alarm; walls crack; laster falls <1000 <6.1 <br /> VIII Destructive Moving cars uncontrollable;masonry <2500 <br /> fractures,poorly constructed buildings <br /> dama ed <br /> IX Ruinous Some houses collapse;ground cracks;pipes <5000 <6.9 <br /> break o en <br /> X Disastrous Ground cracks profusely;many buildings <7500 <7.3 <br /> destroyed;liquefaction and landslides <br /> wides read <br /> XI Very Disastrous Most buildings and bridges collapse;roads, <9800 <8.1 <br /> railways,pipes and cables destroyed;general <br /> tri erin of other hazazds <br /> XII Catastrophic Total destruction;trees fall;ground rises and >9800 >8.1 <br /> falls in waves <br /> Source:Local Hazard Mitigation Planning Manual,North Carolina Division of Emergency Management, 1998,p. 75. <br /> 23 <br />