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(b) Earthquakes are measured in terms of their magnitude and intensity. Magnitude is the measure of total energy released and intensity is the resulting degree of damage caused by an earthquake. Several techniques are used to measure these events. The Richter scale is a standard scale used to compare earthquakes. It is a logarithmic scale, meaning that the numbers on the scale measure factors of 10. An earthquake that measures 4.0 on the Richter scale is 10 times larger than one that measures 3.0. On the Richter scale, anything below 2.0 is undetectable to a normal person and is called a microquake. Microquakes occur constantly. Moderate earthquakes measure less than 6.0 on the Richter scale. Earthquakes measuring more than 6.0 can cause significant damage. The maximum quake rating ever measured is about 8.9. The Mercalli Scale is a subjective evaluation of the effects of an earthquake as evaluated by people in the area. Table A -3: Earthquake Ma nitude and Intensity Scales RICHTER MERCALLI INTENSITY DESCRIPTIONS OF EFFECTS SCALE SCALE I Instrumental Detected only by seismographs Less than II Feeble Noticed only by sensitive people. 4.2 III Slight Resembling vibrations caused by heavy traffic. IV Moderate Felt by people walking; rocking of freestanding objects. Less than V Slightly Sleepers awakened and church bells ring 4.8 Stron Less than VI Strong Trees sway, some damage from overturning and 5.4 falling objects. Less than VII Very Strong General alarm, cracking of walls. 6.1 VIII Destructive Chimneys fall and there is some damage to buildings. Less than IX Ruinous Ground begins to crack, houses begin to collapse 6.9 and pip es break Less than X Disastrous Ground badly cracked and many buildings are 7.3 destroyed. There are some landslides. Less than XI Very Few buildings remain standing; bridges and 8.1 Disastrous railways destroyed; water, gas, electricity and tele hones out of action. XII Catastrophic Total destruction; objects are thrown into the air, much heaving, shaking and distortion of the ground (c) Earthquakes are relatively infrequent but not uncommon in North Carolina. From 1568 to 1992, 157 earthquakes have occurred in North Carolina. North Carolina's vulnerability to earthquakes decreases from west to east in relation to the Eastern Tennessee Seismic Zone. Cabarrus County lays on the far eastern edge of the most active region in the state. The USGS Seismic Hazard Maps indicate that the Cabarrus County region has an 8 -10% probability of earthquake ground motion. Cabarrus Annex A Hazard Identification and Analysis A -7 1 DecemihenmWbi %tuber s F -6 Page 111