The document describes Natalie Bolen's experience of an earthquake in southern Indiana in 2008. She felt her room shaking and wonders what caused it. The earthquake was located on the New Madrid fault line, a zone of deep cracks in the earth's surface. Scientists use seismographs to measure earthquakes on the Richter scale and by intensity levels. The region has experienced earthquakes since 1811-1812, and there is potential for future quakes due to reactivated ancient faults.